 Hey everybody, Dr. O here, chapter seven on energy metabolism. So this is complicated, right? I've had students that I have taught this concept to three, four, five different classes and in some ways it's just one of the most difficult things to grasp that there is. In this video I will try to keep it at more of a high level overview, kind of that 10,000 foot view. I already have a playlist of videos that cover metabolism, that cover it in depth. I mean, every step of every metabolic pathway, including the breakdown of fat for fuels. So here we're just going to look at the big picture and I think that's going to be plenty. Because I do not think that this is as relevant. So when you think about metabolism, I don't think that how our food is turned into fuel is as clinically relevant as the other things we've talked about, right? Like the quality of the food that you eat or even our next chapter on maintaining energy balance. The calories your body produces versus how many it needs, those kind of things are way more important. So I am going to kind of be skimming through a few of these areas but only because I do think that they're not as significant and not as important. If you want the real detailed breakdown, then go to the YouTube channel and find the metabolism playlist. It's super, super in depth. It covers everything from the fed versus the fasted state, the metabolic pathways, heat production and how our body deals with that. All those things are covered there. Okay? All right, let's go ahead and dive in. So the ice breaker, this one's kind of all over the place but what happens when you don't eat or eat too much? Well, we'll talk about that, we'll talk about the fed versus the fasted state. We'll talk about fasting and starvation which are not exactly the same thing. We'll look at how, but basically your body is always eating, right? So whether you ate an hour ago or have an eight in 24 hours, doesn't matter at the cellular level because your cells are constantly eating, right? They're constantly breaking down fuel because they constantly need energy. So it's just the question is, is the energy you're using right now coming from your GI tract because you just had breakfast or is it coming from body fat stores or coming from muscle or liver glycogen? So we'll talk about all that. Do different foods help you do different activities? Yeah, I mean obviously that's why I always say, especially when it comes to your energy sources which are primarily carbs and fat, right? Because protein is not primarily an energy source, protein is a building block. So everyone should meet their protein needs. And then whether, you know, the mixture of fuel that you use, the mixture of carbs and fat you use should really be determined by what works best for you, but also your activity level, right? If you're an endurance athlete, then your fuel mix should be higher carb, lower fat. If you do a lot of walking and you're sedentary, then maybe you'd be fine with a higher fat, lower carb diet. So I do think that the type of activity that you were completing in a day should determine your food intake. I know that I changed the fuel mix that I eat on days that I train. I eat more carbs and less fat. On days that I don't train, I eat more fat and less carbs. So, oh, let's see. What else about that? That's why I talked about this in the carbohydrate lecture, but I always like to say that, you know, if you run marathons, you should eat a lot of carbohydrates. If you eat a lot of carbohydrates, you should run marathons, right? That's kind of to me. That's the first thing I think of when it comes to letting your activities determine the foods you eat. What foods help you most when you're studying? I don't know. I actually, when I want to be really mentally focused, I don't eat. So I just find that it's easier. If I was busy studying, it'd be kind of one less thing to worry about. But if you're hungry, obviously that can be distracting. So I don't think I really had any specific go-to snacks when I was a student. But maybe you do. Oh, when you go out with friends, what do you eat? When you need to relax for the evening, what do you eat? The point is we eat different things based on what we're doing and how we feel and all those kind of things. I always like to talk about how when we're hungry, angry, lonely, or tired, they call it halt. That's generally when you might be hungrier, but also when you might make poorer food choices, right? I was just reading an article this morning about how poor sleep, right? If you didn't sleep well last night, then your body is going to produce more grayling, which is the hunger hormone that makes you hungry. It comes from your stomach and it's going to produce less leptin, which is the hormone that tells your brain that your body already has plenty of stored energy in it. So in that situation, you're generally going to eat more. And then when we're sleep deprived, we also generally make poorer food choices, right? When you're stressed, you generally crave broccoli, you crave sugar, things like that. All right, let's go ahead and dive in. So the learning objectives. Identify the nutrients involved in energy metabolism and the high energy compound that captures the energy released during their breakdown. So that's talking about the macronutrients that we can turn into fuel, you know, carbs, fats, and proteins, and even alcohol. And then the high energy compound that captures that energy is ATP, adenosine triphosphates. We'll cover all that. Summarize the main steps in the energy metabolism of glucose, glycerol, fatty acids, and amino acids. So we'll cover the big picture here for sure. But if you want the more detailed, then go find the metabolism playlist. Explain how in excess of any of the three energy yielding nutrients contributes to body fat and how an inadequate intake of any of them shifts metabolism. So again, as we'll see, your body can turn excess calories into fat. It does not matter where they came from, carbs, fat, protein, or alcohol. Your body can turn them into excess fat. And then how inadequate intake of any of them shifts your metabolism. So we'll talk about like, if you're on a low carb diet or a ketogenic diet, you're purposely shifting your metabolism to one that can't rely on glucose as much. So it has to create this alternate fuel source called ketones. Okay, the chemical reactions in the body. So a lot of terminology, that's the first thing with metabolism is what is metabolism and then covering a lot of terminology. So we can start there at the bottom with what is metabolism. So it says here, it's how the body uses foods to meet its needs. So how I like to define metabolism, I didn't make it up. But the sum of all the chemical and physical processes that are occurring in your body, right? So everything happening in your body is part of your metabolism. So also how I like to define metabolism is some terms you'll see on probably the next slide. Metabolism is catabolism plus anabolism. So I'll come back to that. But the sum of all the chemical reactions occurring equal your metabolism. But before we get there, energy. Energy is in different forms, right? I mean heat, mechanical, electrical, and chemical energy. And your body uses all of these, right? Our metabolism generates a ton of heat. Obviously mechanical energy is moving things around and we are electrochemical systems. So tons of electrical and chemical energy occurring in the human body. Photosynthesis, on the other hand, is what plants use. So the process in which green plants use the sun's energy to make carbohydrates. Basically, all food is including you, all food, all cells, are packets of stored sunlight energy, right? All the energy stored in your body right now and all the energy you're going to use today came from the sun. Because the sun, through photosynthesis, generated the energy needed for those plants to make themselves and to make their fuels. And then we eat those plants or we eat the animals that ate those plants. Or we eat the animals that ate the animals that ate those plants. But the point is, all energy came from the sun. So you are stored packets of sunlight energy. That's the best way that I can describe you and where we fit in these food chains and where we fit in these metabolic pathways. Fuel. So just like the fuel in your car, compounds that cells use for energy. So your car uses hydrocarbons. So next time you go, look at your fuel and you look at your gas, it gives those hydrocarbon ratings. So you put fuel in your car and your car will use that to generate the energy it needs to do its jobs. Well, that's exactly what your body does. You see your glucose, fatty acids and amino acids, all of those are hydrocarbons, meaning that they have carbon and hydrogen. So you and your vehicle are shockingly similar. You put fuel in your gas tank, in your car, you need fuel and we need air. And we use those two things to power the movement of the car. And then we produce waste products, like it comes out of the tailpipe of a car. Well, same thing for you, right? You need hydrocarbons, so you consume carbs and fats and other fuel sources. You need oxygen to power your metabolism and you generate waste products, carbon dioxide and water. So there's a lot of similarities there. So those are the fuels we'll talk about quote unquote burning today. And then metabolism, how the body uses foods to meet its needs. And we talked about that and I'll give you a more sophisticated definition real soon. One last thing about the fuel, right? Just a little kind of tidbit here is if you're burning, we talk about burning fuel and burning fat. Well, if you burn a pound of fat, where does it go, right? If you know, I've lost quite a bit of weight and where did all that fat go? Well, if you're basically, if you're burning a pound of fat, then you're turning it into waste products. So when you burn a pound of fat, 84%, 85% of it is going to become carbon dioxide and 15%, 16% is going to become water because those are the quote unquote waste products of our metabolism. So if you've lost a pound of fat, you basically are exhaling it as carbon dioxide and then you're turning it into water, which will maybe become urine. So you're breathing it out and peeing it out basically. That's what happens when you burn a pound of fat. All right, let's reflection questions. So uses energy to build compounds. That's called anabolism. Are the most metabolically active of your body cells, your liver? So let's actually go through these. So anabolism is anytime you use energy to build something. And then D, on the bottom, when you break compounds down and release energy, that's called catabolism. So I mentioned earlier that your metabolism is the sum of all the anabolic reactions that occur in your body and all the catabolic reactions. So what are some good examples? Digestion. Digestion is catabolic. You're breaking and digesting. You're breaking the food down that you eat and releasing energy and building blocks as you do so. So digestion is catabolic. Then you absorb and you take those building blocks and you take the energy that you created and you use it to build you. So if you eat a pound of chicken breast and you catabolically digest it and break it down, you now have all those amino acids and all that energy. You take those amino acids, take that energy and you build a pound of you. It wouldn't be a pound because whatever, but not even close. But still, you get the point. So all the catabolic breakdown reactions in your body plus all the anabolic buildup reactions of your body, you put those together and the sum is your metabolism. All right, so back to B. Are the most metabolically active of body cells? It says your liver and that's true. Gram for gram, your liver and your brain are the most metabolically expensive tissues that you have. When you think about your metabolism, you often hear people talking about muscle and how metabolically active muscle is. Well, muscle cells are not near as metabolically active as liver and brain cells are, but you have so many more of them, right? I mean, at least by weight. So yes, if you want to increase your metabolic rate, you need more muscle. You need more lean tissue. You can't grow another liver. You can't grow another brain. If you could, then that's what you should do, because your metabolic rate would skyrocket. But you can grow muscle, you can build muscle. If you add a pound of muscle, it might only be worth. A few calories a day, right? We used to think, when I was in college, people talked about a pound of muscle burning 50 calories a day or something. We now know the number is probably somewhere in the neighborhood of like 6 to 10 calories a day. But still, that adds up. Over 365 day a year, over a 10 year decade, a few pounds of muscle will really add up. But to me, the main reason that adding muscle is the best way to improve your metabolic rate is because it takes a lot of calories to build a pound of muscle. So not only once you've built a pound of muscle, does it burn more energy for you on any given day. But let's say it takes 23 or 2400 calories to build that pound of muscle. So you've invested a bunch of calories in building the muscle, then you invest calories every day of your life maintaining it. And then if you're strength training or doing things that are going to build muscle, then there's constantly damage and repair, damage and repair. So I do think that putting on a few pounds of muscle can absolutely improve your metabolic rate more than just that handful of calories. But yes, it is true that the liver is more metabolically active than your muscle. See how the body obtains and uses energy for food? That's going to be your metabolism that we just talked about. So it obtains the energy through catabolic reactions, uses it in anabolic reactions, and that is your metabolism. Excuse me. All right, so here a little overview of the cells. So hopefully you've covered this in your anatomy classes. But the big parts here when it comes to metabolism, we're looking at on the left hand side here, the cytoplasm. So the cytoplasm is just the guts of the cell, and that's where glycolysis occurs. So the huge majority of your metabolism is actually occurring inside what's called the powerhouse of your cell or the mitochondria. Over here on the right, there's more than one of them. But so we always say that the mitochondria is the powerhouse of the cell. This is where 95% of your ATP is produced, and that is true. The other 5% is happening with glycolysis out in the cytoplasm. So glycolysis occurs in the cytoplasm of the cell. Then all the other steps we're going to talk about, like the intermediate step, the Krebs cycle, which is here, it's called the TCA cycle. Fats are broken down in the mitochondria. All those things are happening in the mitochondria. So the cytoplasm, as you see here, the guts of the cell, the cytosol is just the fluid portion. The cytoplasm is all the guts. So the cytosol is where glycolysis occurs, and then everything else occurs over here in the powerhouse of the cell, your mitochondria. All right, these terms, anabolic and catabolic, we've been talking about them for a while now. Anabolic reactions, they require energy and they build things. So here you see glucose being built into glycogen. You see a glycerol and fatty acids being built into triglycerides or fats. And you see amino acids being built into proteins. Those are anabolic reactions that require energy. And they also would be, just to review a term we've used several times now, it would be condensation reactions that build them, where you remove water as you build things. Catabolic reactions are going to be the opposite when we break things down and they release energy. So when glucose is turned into glycogen, that takes energy. When glycogen is turned into glucose, then it can release energy. And then so it's everything in reverse. Glycogen becoming glucose and then burning that for fuel. Triglycerides being broken down into a glycerol, which can be turned into glucose or burned for fuel. And fatty acids, which can be beta-oxidized for fuel, so that's the term you'd use, and then protein broken down to amino acids. And can be used for fuel. We don't think of them as a great fuel source. Proteins, you should think, building block first and they can be a fuel source. Carbs and fats are primarily fuel sources. All right, so that's your anabolic and catabolic reactions again. Transfer of energy, then we have ATP. ATP or adenosine triphosphate is the currency that your cells use. When you store energy, you store it as ATP, which we can't store very much, but you store a little bit of it. And then when we spend energy, this is the currency we use. So whether you're eating glucose or whether you're eating carbs or fats or proteins or ketones, none of it matters. Your body's job is to turn it into ATP. So I like to think of it like a currency. So imagine being a currency exchange. You show up here in the United States and you've got, I don't even know, you've got money from five different countries and it doesn't matter which countries they are. You would need to take it somewhere to exchange it into the American dollar, into our currency. So that's what ATP is. So alcohol, that's money from Germany and carbohydrates is money from France. I'm just making these things up, I don't know. Fat is currency from India. The goal is to turn all of it into ATP. So ATP is the energy currency of the cell. Another reason I like calling it a currency is that just like with real money, we're much better at spending it than we are saving it, right? We generate massive amounts of ATP, like unbelievable amounts. I mean, you need a constant supply of ATP or you'd be dead in an instant. Let's just say for a fact, your body makes so much ATP every day that if you were to take every ATP you needed today and put it in a pile and weigh it, it would weigh about half as much as you. So how does that happen? Well, it's because it's used and reused and reused. There is no pile of ATP. But if you counted how many ATP it took you to survive today and you weighed it, it would be in the kilograms, 40, 50 kilograms, something like that. So we need massive amounts of it, but we really suck at saving it. We can only save like a couple of seconds worth of ATP. Your metabolism has to constantly be running because the moment it stops, you run out of ATP and you're dead, right? So ATP, we have two, three seconds worth of it stored in our body right now. So we're really good at spending it, not really good at saving it, just like most people with money. Okay, so ATP or adenosine triphosphate is the high energy compound that powers all activities and living cells. It contains three phosphates. That's why it's called ATP, adenosine triphosphate. And as it's broken down and releases its energy, it becomes adenosine diphosphate. I'll show you a picture in a moment, but you lop off the third phosphate and you extract the energy from the bond that was holding it on there. And that's the point next, readily hydrolyzed and releases energy. These bonds are high energy bonds because they're unstable and they will release very easily. And as they do so, that's how we use the energy to power our processes. Just like if I have a dollar in my hand, well, that's stored income, stored money. And if I use it, I can make something happen, right? I can buy an ice cream cone or whatever. Okay, so the reactions that generate energy are called coupled reactions because as you see here, energy is simultaneously consumed by reactions as energy is produced. Well, so as we produce energy, the energy that's consumed is heat. So almost half of the food energy that's converted to cellular energy is lost as heat, right? Our metabolism is actually quite efficient compared to other animals, but still we waste more than half the energy in our body and most of that is lost as heat. So the reason that I'm sitting here at 98.6 degrees, this furnace, is that I'm constantly generating heat as a byproduct of my metabolism. All right, so here we see adenosine triphosphate. Do you notice the three green phosphates here? And the reason that these red lines are wavy is because these are high energy bonds because they're unstable. So when you build an ATP, so you take an adenosine diphosphate and you add energy in a third phosphate to generate ATP, it now has stored energy in it. When you release that third phosphate, it releases energy and that's why ATP powers your metabolism. All right, so I'll just read what it says here. Excuse me, bonds connecting the three phosphate groups are indicated as wavy lines indicating a high energy bond because they're unstable. When bonds are broken, energy is released. So just remember ATP is like stored energy, ADP is spent energy and that's why I love this analogy right here. It's like a rechargeable battery. So just like the rechargeable batteries you have in your junk drawer somewhere, ATP is a charged battery and you put the battery, whether you put the battery in a microphone or whether you put it in a toy, my son is using an RC car the other day that had some batteries in it, doesn't matter where you put the battery, the battery will release its energy to power a process that's just like what happens in your body. So let me read point one here. Energy is released when a high energy phosphate bond in ATP is broken. Just as a battery can be used to provide energy for a variety of uses. The energy from ATP can be used to do most of your body's work. Contract muscles, transport compounds, make new molecules and more. With the loss of a phosphate group, high energy ATP, which is like a charged battery, becomes low energy ADP, a used battery. But remember, these are rechargeable batteries. When this battery dies, you don't throw in the trash. When this battery dies, you go and recharge it so you can use it again. That's why, even though I need 40 or 50 kilograms, like I said grams earlier, but it's a much bigger number than that, even though I need half my body weight in ATP every day, I don't need that many of them because each one can do its job thousands and thousands and thousands of times. So it's not, you don't use ATP and throw it away, you use ATP, turns into ADP, you recharge it and you use it again and again and again. All right, so these are like the world's most efficient, most successful rechargeable batteries. So step two, so you see here, we've turned ATP into ADP when we release that phosphate and we release that energy. Now we got to rebuild it and that's what your metabolism does, right? The reason you eat, the reason you eat carbs and fats and all these things is so that you can power the reactions that turn ADP back into ATP. So you can use it again and again. All right, energy is required to recharge the battery as a phosphate group is attached to ADP, making ATP. Just as a used battery needs energy from an electrical outlet to get recharged, ADP needs energy from the breakdown of carbohydrates, fats and proteins to make ATP. So that's a super cool analogy. All right, there's a lot of nuance here. We have another temporary method of recharging ADP called the creatine phosphate or phosphocreatine system, but I don't think we really need to dive into that. I have that covered in the metabolism playlist I told you about earlier. The helpers in metabolic reactions are enzymes and coenzymes. So your metabolism, enzymes are wickedly important. They're considered biological catalysts. They greatly speed up our metabolic rate or because they greatly speed up or they make reactions a lot cheaper. So without enzymes, our metabolism just wouldn't work. Enzymes speed up chemical reactions a million to a billion times. Enzymes can be used up to 10, the same enzyme can be reused up to 10,000 times a second. I mean, they're amazing. So your metabolism, we could not survive without enzymes. So enzymes are proteins that power all the steps in our metabolic reactions, but enzymes aren't enough. Enzymes are like the engine, but coenzymes are needed. Coenzymes are like the ignition, like the starter in your car with a key. So coenzymes are organic and what that means is they're carbon-based. These are gonna be vitamins. So the reason, everyone knows we need vitamins and minerals, but why? One of the main reasons we need vitamins is because they turn on our enzymes. So you see here at the bottom, without a coenzyme, an enzyme cannot function. So like with your car sitting there without its ignition isn't going to start and isn't going to run. The coenzymes are what turn on the engine that power these enzymes. So when we talk about like energy vitamins, you might hear people talk about B vitamins, for example. Well, why? Well, B vitamins power the metabolic steps that turn carbs and fat into fuel and protein, but the carbs and fat are the big ones. So that you think about like, for example, we'll cover some of these, but niacin, one of your B vitamins, that creates an electron carrier that we need to generate energy. Riboflavin does the same thing. We need all of these. All right, so that's the importance of vitamins in your metabolism. They don't actually generate energy. It's like a B vitamin doesn't have any calories. So it's not worth any energy on its own. So what vitamins do is they allow you to extract energy from your food. So there's no calories in a B vitamin. They do not directly provide energy, but they power the process that allows you to get energy from your food. Our reflection number two. This is a review of things we've covered over the last several chapters. Carbohydrates are broken down during digestion to become glucose and the other monosaccharides, which remember, we are three monosaccharides or glucose, fructose, and galactose. Big difference is fructose and galactose have to then be turned into glucose by your liver. Two, fats or triglycerides, remember they're called that because they have the glycerol backbone and three fatty acid tails. So triglycerides are broken down to form that glycerol and the fatty acid tails. And then we'll see how glycerol can be burned for fuel and then also how the fatty acids are beta oxidized to become fuel or to be burned for fuel. Three, proteins are broken down into individual amino acids and we'll see that they can be burned for fuel as well. And these are all examples of catabolic reactions because we're breaking things down and releasing energy. Breaking down nutrients for energy. All right, so the simplified overview of the energy yielding pathways and I'll show you a picture in a moment. All of the energy yielding nutrients, protein, carbs, and fat, but this is a quick reminder, proteins should never be seen as an energy source first. Proteins are building blocks. When we don't have carbs and fat and we don't have enough of them, then yes, we can rely on protein as a fuel source. All right, so all the energy yielding nutrients, proteins, carbohydrates, and fats can be broken down to acetyl-CoA. I like to call acetyl-CoA the keystone of your metabolism. This is that, so we're talking about that energy currency earlier. Really, this is the exchange station. Oh, your alcohol, your carbs, your protein, your fat, I'm gonna turn all of you into acetyl-CoA. And then once that happens, and acetyl-CoA enters the TCA cycle, which TCA stands for tri-carboxylic acid cycle, but I will call it the Krebs cycle, or the Krebs citric acid cycle. Once acetyl-CoA enters the Krebs cycle, your body doesn't care where it came from. So really, the first step of generating energy is to take whatever you consumed for fuel and convert it to acetyl-CoA. And then acetyl-CoA will run down and the following steps will generate ATP. All right, so we've turned our proteins, carbs, fats, or alcohol into acetyl-CoA. Acetyl-CoA enters the Krebs citric acid cycle. And then during these metabolic reactions, most of the reactions above release hydrogen atoms with their electrons, which are carried by coenzymes to the electron transport chain. So this is going to be, the carriers there are called NADH, which comes from niacin, and FADH2, which comes from riboflavin. And that's where most of the energy is gonna come from, and as you'll see if you watch the more detailed videos, as you're going step by step through this process, then electrons and hydrogen ions are being harvested and they're gonna be taken to the electron transport chain. So how I like to describe that is like a casino, right? So as you're going through these energy-yielding steps, you're getting casino chips. So these electron carriers to me are like casino chips. And each NADH is a casino chip that's worth three ATP. Each FADH2 is a casino chip worth two ATP. Why do I call them casino chips? Because right now in my hands they're worth nothing. I have to take them to the cashier to give them value because then they'll turn them into real money. The cashier is the electron transport chain at the end. You harvest electrons and harvest hydrogens and then you take them to the cashier, which is the electron transport chain, and they're turned into ATP. So that's the next point there. ATP is gonna be synthesized in this electron transport chain primarily. And then hydrogen atoms react with oxygen to produce water. So the equation of your metabolism is glucose or whatever fuel you're using, but we usually talk about glucose first. So glucose plus oxygen, right? We need oxygen to power our metabolism. So glucose plus oxygen leads to carbon dioxide, water, which you see here being produced. So carbon dioxide is a waste product and water is a waste product, but everybody uses it. Carbon dioxide, water, and ATP, the energy that our body needs. And if you take a typical glucose and you fully oxidize it like that, you will turn that one glucose into 36 ATP when you're dealing with eukaryotes like humans. All right, discussion question one. What are pyruvate and acetyl-CoA and what is their role in glucose production in the body? So we haven't gone through the steps here, but so glucose starts with six carbons. Its chemical formula is C6H12O6. After glucose runs through glycolysis, it's been split in half into two of these pyruvates, which are three carbon structures. And then the next step in your metabolism, you actually lop off one of those carbons and you turn a three-carbon pyruvate into a two-carbon acetyl-CoA. Now where does that third carbon go? It's fused with oxygen and becomes carbon dioxide. We're actually, we exhale the fuel. So if you had pancakes this morning, you're exhaling the carbon skeleton of those pancakes as carbon dioxide, basically. All right, so pyruvate, a three-carbon structure and acetyl-CoA, a two-carbon structure with what's called a coenzyme CoA attached to it, that's why it's called acetyl-CoA, and that comes from a B vitamin called pantothenic acid, are two new fuels used by the body. Pyruvate can be used to make glucose. Acetyl-CoA cannot because that means, so basically pyruvate is a reversible reaction. You can turn like glucose into pyruvate and then pyruvate can become acetyl-CoA and then run through the Krebs cycle and get burned for fuel. Or pyruvate can go back and become glucose. Acetyl-CoA can't. Once you have acetyl-CoA, it enters the Krebs cycle and it's going to be metabolized. Or it can be turned into ketones. That's a whole separate discussion. All right, a simplified overview. There's nothing simple about any of this, I get it, but a simplified overview of the energy-yielding pathways. So here we see proteins, carbs, and fats, and we'll just go in this order, but just a reminder that, you know, proteins can be burned for fuel, but they have more important jobs. And that's because proteins where we get our nitrogen. We can get carbon, hydrogen, and oxygen from any of them. We need, we should be using our proteins for things that require nitrogen first. All right, so protein is digested to amino acids and then you see we have, I'll cover this in more detail later, but we have some of our amino acids, they can become pyruvate. So those are going to be called glucogenic amino acids. Some of our amino acids are going to directly become acetyl-CoA. Those are called ketogenic amino acids, because like I just mentioned earlier, acetyl-CoA can enter the Krebs cycle or be turned into ketones. And then we have some amino acids that are going to directly enter the TCA cycle or the Krebs cycle, and those are also called glucogenic amino acids. So protein digested to amino acids, burned for fuel, depending on the amino acid, it's going to happen a different way. Carbs are going to be turned into glucose, whether if you ate sugar, for example, you're going to digest it into a glucose and a fructose. And your liver's going to turn that fructose into glucose. Now we have glucose and we burn it. If you ate starch, it's long chains of glucose. We digest them to individual glucosees. Now we have glucose, we burn it. Your bite doesn't care the difference. Your starch, sugar, all carbs, except for fibers, because they're not digested, are going to end up their end, the end result is glucose. So carbs are turned into glucose, which will be turned into pyruvate during glycolysis, and then they'll become acetyl-CoA, and then run through the Krebs cycle and then generate energy in the electron transport chain. Fat has two destinations, because remember, fats that try glyceride, the glycerol backbone of fat can become pyruvate and then can become glucose. So glycerol is going to be, that's called gluconeogenesis. Whenever you turn a non-carbohydrate into a carbohydrate, it's called gluconeogenesis. So that's what's happening there with glycerol. Then the fatty acids are going to be beta-oxidized where they become, so a fatty acid has these long tails, and remember from last chapter, two chapters ago, sorry, they're all even numbers, so 16, 18, 20 carbons. Well, those carbons are lopped off two at a time, and they become acetyl-CoA, so that, and then they're going to be, that's this beta-oxidation process. Acetyl-CoA will be burned for fuel. All right, so step one, all the energy yielding nutrients, protein, carbs, and fat can be broken down to acetyl-CoA, that's why I call that the keystone of your metabolism. Acetyl-CoA then enters the Krebs citric acid cycle, where you generate all these hydrogens and all these electrons, which then enter the electron transport chain. So number three, most of the reactions above release hydrogen atoms with their electrons, which are carried by coenzymes, that'd be your NADH and FADH2, to the electron transport chain. Step four, ATP is synthesized. Step five, the waste products. Hydrogen atoms react with oxygen to produce water, and carbon atoms react with oxygen to produce carbon dioxide. So we take our fuel, glucose or whatever, plus oxygen, and we make carbon dioxide and water, and we make ATP. That's the overview of how you generate energy. All right, reflection three. You know, feel free to pause these and look at these before I jump ahead. Glycerol and amino acids can provide glucose because they can be converted to peruvate. We talked about that. Fatty acids are converted to acetyl-CoA, that's called beta-oxidation. Acetyl-CoA is the compound that enters the citric acid cycle or the Krebs cycle, and that's why, again, your body doesn't care where it comes from, whether it's protein, carbs, fat, alcohol, it wants to turn it into acetyl-CoA so it can power its metabolism. Number four, energy is harnessed through the electron transport chain. Okay, and this is where I'm really gonna be kind of skimming, because I have videos where I go through great detail through all these processes, and I think they'll really help you because you'll see them better as well. But the first step, so we're gonna start with glucose, and then we'll look at fats and proteins separately. So glycolysis is how we turn glucose into pyruvate. Remember, glucose is a six-carbon structure, C6H1206. Glycolysis means the ripping or tearing apart of glucose, so you take a six-carbon glucose and you split it in half. So if you started with one six-carbon structure, you now have two three-carbon structures, which are pyruvate. And then you see their hydrogen atoms are carried to electron transport chains, so during glycolysis, as you split glucose in half, it does generate some energy. It's called a net gain of two ATP, and the reason we say it that way is because you have to spend two ATP, it's called the energy investment phase, to create four ATP, the energy payoff phase. So glycolysis yields a net gain directly of two ATP. But then during glycolysis, you're going to fill up two of these electron carriers called NADH, and each NADH is worth three ATP. All right, so that's glycolysis. Then normally, pyruvate will go on and just depends on how much oxygen is available, how much energy you're using. Pyruvate will generally go on to become acetyl-CoA, but we'll look at the other options. But yes, pyruvate can be converted back to glucose. Your liver cells and some cells in the kidneys can do that, and we'll come back, we'll talk about the core recycler and how your body recycles these different things. So normally, glucose is becoming pyruvate, but pyruvate can be converted back to glucose, and that's gonna be how your body can really turn things, non-carbohydrates, into glucose. All right, so what are pyruvate's options? So after you've turned glucose into pyruvate, really it depends on if you have the presence or absence of oxygen. If there's not a lot of oxygen, so if you're intensely exercising, you're running as hard as you can, or something like that. If you need to generate energy really quickly in this anaerobic environment, pyruvate is gonna become lactate, and that's where people talk about feeling the burn with their muscles and these kind of things. The reason that happens, and we'll go into a little more detail in this, but pyruvate becomes lactate so that glycolysis doesn't shut off. In an anaerobic environment, if this pyruvate just built up, then our glycolysis would shut off, and we'd have no energy, because without oxygen we can't power our metabolism, except for this first step, glycolysis, because it's anaerobic. But if it shuts off, then it stops generating energy, and basically anytime you tried to exercise intensely, you would die. So the reason people think about lactate is a bad thing, which it absolutely isn't. Pyruvate becomes lactate to get it out of the way so that glycolysis can continue to run, and you don't die when you're on the treadmill. All right, so in an anaerobic environment, pyruvate becomes lactate, and then your body can recycle the lactate later. We'll come back to that once you have oxygen. If you're in an aerobic environment, so if you're at rest or you're just taking a walk, you're doing simple things like that, then pyruvate will continue on to become acetyl-CoA, and that conversion of pyruvate to acetyl-CoA is called the intermediate step. During that step, no energy is produced, so no ATP, but we do get two more of those NADHs, those electron carriers, so we harvest some more hydrogens and electrons. So now after these first two steps, so after glycolysis, we had two ATP produced and two NADHs. After the intermediate step, we're still at two ATP, because we didn't make any more, but there's now two more NADHs. So we've made two ATP, a net gain of two ATP, but now we have four of these NADHs. Those are those casino chips I was talking about that each have three, or each were three ATP when we cash them in later at the electron transport chain. Okay, so in an anaerobic environment though, pyruvate will accept those hydrogens to get them out of the way, so glycolysis can keep running, and it'll turn pyruvate into lactate. Like I see here, it does occur to a limited extent at rest. We always have some lactate. Lactate's a great fuel source. I think lactate and ketones are both so misunderstood that I think they can be phenomenal fuel sources there. I mean, they're alternate fuel sources there for a reason. All right, but they produce ATP quickly, just not very much, right? So that's an issue. So lactate does accumulate in your muscles. People talk about that being part of the reason that muscles fail and the burning sensation. I don't know how much that's true. They're still trying to tease all that out. The corey cycle will cover in more detail in a moment, but the corey cycle is then how? So if you generate all this lactate when you're in an anaerobic environment, what happens when oxygen reappears, when you stop exercising, for example? Well, the corey cycle is how you take this lactate, you turn it back into pyruvate, and then you can turn it back into glucose. So really, if you're doing really intense anaerobic exercise, you're not even really using glucose, you're borrowing it. You're turning glucose into pyruvate and then lactate, and then you're gonna turn lactate back into glucose. Now, it does take energy to do that, but still, you can recover a lot of the glucose that you quote-unquote spent during intense activity. Maybe you're doing like high-intensity interval training or really anaerobic activities. Maybe you're an MMA fighter or something like that. All right, so here is the corey cycle. So working, excuse me, my nose always itches when I do these things. All right, working muscles break, so number one, working muscles break down most of their glucose molecules to pyruvate, releasing energy in the form of ATP. All right, that's glycolysis. You see that the six-carbon glucose was turned into two, three-carbon pyruvates, and we generated the net gain of two ATP while we did so. And then your NADH is capturing the electrons, the E with a minus sign there, and the H plus, the hydrogen ions of the protons. Those are gonna be cashed in later. All right, if the cells lack sufficient mitochondria or which like a red blood cell doesn't have any, or in the absence of sufficient oxygen, pyruvate can accept the hydrogens from glucose breakdown and become lactate, which is happening over here. This conversion frees the coenzyme so that glycolysis can continue. So people look at lactate like it's a bad thing, but like I said, if you didn't generate lactate, then glycolysis would shut off, and you would be on your stair stepper and you would die. So consider that. All right, step three. So you see that lactate's gonna travel to the liver. The liver enzymes can convert lactate back to glucose. This is the corey cycle. This reaction requires energy. So lactate becomes glucose again. Glucose can then go back out into the body and do its job. So when you're doing intense anaerobic activities, you're borrowing glucose more than you're actually burning it, but it does waste energy. It takes energy to turn lactate back into glucose, but at least we get it back and we get some of the energy back. All right, that's the corey cycle. I have a whole video on that if you wanna go into more detail. The paths of pyruvate and acetyl-CoA. So here you see whether these arrows are pointing in one or two directions is really the key here. So glucose can become pyruvate, but then pyruvate can also become glucose. Talked about that. Let's go over here. Glycerol, so the glycerol backbone of your fatty acids can be, can it actually enter somewhere between glucose and pyruvate. So it can either become glucose or it can be burned for fuel by becoming pyruvate. And the absence of oxygen becomes lactate, but then it can be reversed and turned back into glucose once you have oxygen. Fatty acids can be turned to acetyl-CoA and acetyl-CoA can be turned into fat. And that's, this is really, this is how your body can turn anything into fat. If you consume excess calories, whether it's carbs, protein, fat, or alcohol, and you have a buildup of acetyl-CoA, it can be turned into fat. Then on this side, we have what are called the glucogenic amino acids, those are the ones that become pyruvate and can be burned for fuel. And then we have the ketogenic amino acids that they become acetyl-CoA and then they're gonna be burned for fuel as well. So you see how acetyl-CoA is really the key. Everything is going to become acetyl-CoA and either burned for fuel or stored as fat. All right, now let's check one, how many carbons are there in glucose? Said a few times here, remember, glucose is C6, H12, 06. And when we split that six carbon glucose in half, we get our two, three carbon pyruvates. And then if there's plenty of oxygen, your three carbon pyruvates become two carbon acetyl-CoAs and then they either can become ketones or they run through the Krebs cycle and are burned for fuel. All right, so now that's talking about glucose. How does your body turn fat into fuel? And this is that process of beta-oxidation is the key term here. So fatty acids to acetyl-CoA pathway. So let's start with the fat at the top. So we digest the fat into a glycerol and then our fatty acid tails. Let's get glycerol all the way. So glycerol is going to enter glycolysis between glucose and pyruvate and really can go either direction. So glycerol can be turned into glucose or glycerol can become pyruvate and be burned for fuel. So you see glycerol, pyruvate, becoming acetyl-CoA, entering the Krebs cycle. That's glycerol and that's maybe about 6% of the stored energy in your body right now is the glycerols from your fats that can basically be turned into glucose in that process of gluconeogenesis. So I'll read a couple of points here, or first one anyways. Glycerol enters the glycolysis pathway about midway between glucose and pyruvate. So we've said that now. So let's forget about the glycerol now. Let's look at the fatty acid tails. So remember all of our fats have fatty acid tails of different chain lengths but they're always even numbers. So that's because we're gonna use these carbons two at a time. So step two, in the first step of fatty acid oxidation the fatty acid is activated by a CoA and you see what you see here. Activated by a CoA and a little energy is used. Number three, CoA enzymes carry hydrogens and they're electrons to the electron transport chain. So while this process is occurring we're gonna be filling up our NADHs which will power our electron transport chain later. Number four, another CoA joins the chain and the bond of the second carbon, the beta carbon, weakens. Acetyl CoA splits off leaving a fatty acid that is two carbons shorter. That's why it's called beta oxidation. So we went from where did we start with? We started with a 16 one here, right? Let's see, yep. Okay, so we had, you have your fatty acid tail, you add these CoAs to it and then you lop off two carbons generating a Acetyl CoA. So this Acetyl CoA will enter the citric acid cycle, the Krebs cycle, just like if it came from carbs doesn't matter and then Acetyl CoA will power the rest of your metabolism and you're gonna lop off two carbons at a time. So you go from 16 to 14 to 12 to 10 to eight to six to four to two. So that's the beta oxidation process. You take these long fatty acid tails, you lop off two carbons at a time and then you burn them for fuel. So this means that fat is a phenomenal fuel source, right? Tons and tons of energy and fat. The downside is beta oxidation occurs really slowly. This is why if you're at rest your body's primarily using fat for fuel, rest to moderate activity. But as activity gets more intense, that oxidation can't keep up. So you have to burn glucose at higher intensities. So the more physically active you are, the more your body will want to burn glucose for fuel. The less physically active you are, the more your body can rely on fat. So fat's a better fuel source, but it's a slower fuel source. We talked about that before, like a log on a fire, right? Fat is like these huge logs. They'll burn all night, but they burn really slowly. If you want the fire to burn quickly or you wanna get the fire started quickly, you add newspaper or twigs, kindling, those kind of things. The kindling will burn up real fast, but it'll start the fire. So glucose is like that. Glucose is not a great fuel source, but it burns really quickly. Fat, phenomenal fuel source, but it burns really slowly. Okay, the last step there, the shorter fatty acid then enters the pathway and the cycle repeats itself and we keep lopping off two carbons until they're gone. All right, so we said all this, glycerol and fatty acids. Glycerol can become glucose or pyruvate. In the process of fatty acid oxidation, fatty acids are taken apart two carbons at a time. They become acetyl-CoA. As this occurs, hydrogens and electrons are released and carried to the electron transport chain. They're gonna use the electron carrier NADH. All right, we've said all this. So fatty acid activated by a CoA. Another CoA shows up. You break off the beta carbon or the second carbon bond weakens and it's split and that's why they come off two carbons at a time. Those two carbons become acetyl-CoA and then the cycle continues until you go, well, what we went from 16 to 14 to 12, the 10 to eight to six to four to two and then that fatty acid tail has been quote-unquote burned for fuel. All right, now switching gears to amino acids. I mentioned all this earlier. We have three different paths that amino acids can take. Most amino acids are glucogenic, meaning they can be converted to pyruvate, which can be used to make glucose. So that's why they're called the glucogenic amino acid. So here we see them becoming pyruvate, which they can either be turned into acetyl-CoA and burned for fuel or they can go backwards and become glucose. That would be that process of gluconeogenesis. But some of them because of their structure become two carbon acetyl-CoA. So these are gonna be called ketogenic amino acids because they're gonna be turned into acetyl-CoA, which cannot then be turned back into pyruvate. So acetyl-CoA is either going to run through the Krebs cycle or it's gonna become ketones, hence ketogenic. And then some amino acids, they're actually gonna enter the Krebs cycle, which I'll show you in a moment. They're gonna enter it at different places on the Krebs cycle directly. And then they'll generate energy. But they're also called glucogenic amino acids. Review the process for breaking down amino acids. We just did it. So you can read through this if you want. Pretty much said all that. Actually, I do want to mention something here. Before amino acids can enter the metabolic pathway, deamination must occur. This removes the nitrogen-containing amino group. Remember, protein has nitrogen on it. If you're gonna use protein to build proteins or use amino acids to build proteins, that's fine. But if you're gonna use amino acids as a fuel source, you have to remove the nitrogen. That's called deamination. That extra nitrogen's gonna become ammonia and then it's gonna become urea and then it's one of the most important waste products that our kidneys get rid of when we make urine. So if you're going to burn amino acids for fuel, you have to deal with the excess nitrogen. And we talked about that in the last chapter. If you're on a higher protein diet, then you should be drinking more water because your body's gonna have to deal with more urea. Some amino acids enter energy pathways after being converted to byruvate. That's the glucogenic ones. Others is acetyl-CoA. That's the ketogenic ones. And then others enter the TCA cycle directly or the Krebs cycle directly. Also called glucogenic amino acids. Amino acids converted to byruvate can make glucose, glucogenic. Amino acids converted to acetyl-CoA can provide energy or be stored as fat. That's how your body would turn excess protein into fat. All right, now we're at the actual Krebs cycle. So we've been through glycolysis. We've been through the intermediate step or beta-oxidation or all these different steps that make acetyl-CoA. Now it's time to put that acetyl-CoA to work. So it's the TCA cycle they call it here, which stands for tri-carboxylic acid cycle. But I like to call it the Krebs citric acid cycle. It was Hans Krebs, I think it was his name, the guy that discovered it. All right, so the final common metabolic pathway takes place in the inner compartment of the mitochondria. So you see that the mitochondria has a double membrane. There's an inner and an outer compartment and it's the membrane between the two where most energy's gonna be produced. It is a circular pathway as you'll see and that means that basically the last step of the pathway is needed to start the first step. So it continues on and on as long as you have the building blocks. And that last step, the four-carbon compound is called oxaloacetate. This would be like low carb diets. What low carb diets do or ketogenic diets do is they run your body low of this oxaloacetate precursor. So you have all the acetyl-CoA you need because you're burning fat for fuel. You don't have enough oxaloacetate and that's where you have, if this cycle starts to slow down, that's where your body will start to generate ketones. So it's actually, it is ketogenic by slowing down the Krebs cycle or at least overwhelming it. Let's put it that way, overwhelming the Krebs cycle. All right, so here we do have the Krebs cycle. So a really big picture. During this Krebs cycle, you'll see here on the bottom, we do generate something that becomes an ATP. So one run through the cycle only generates a single ATP. But the Krebs cycle generates two ATP, because remember, we're talking about glucose, because remember, we started with one glucose and split it in half. So we have to run through the cycle twice. And this is also why fat will generate way more energy because if you have an 18-carbon fatty acid chain, it's gonna make nine acetyl-CoAs, which means nine shots through the Krebs cycle. So you don't generate a ton of energy here, but here's the key. The reason the Krebs cycle is so important is look here. Coenzyme, coenzyme, coenzyme, coenzyme. So one path through the Krebs cycle is going to fill four of those electron carriers, which are those casino chips that we will cash in at the electron transport chain. Later you see here in the bottom of the picture, they're heading to the electron transport chain. So during the Krebs cycle, you only make two ATP, but you fill six of those NADHs, and each one of those is worth three ATP, and you fill two FADH2s, which is the other electron carrier we've been talking about, and each of those is worth two ATP. So we're winning a bunch of the casino here. We're not making a lot of money yet, but we're filling up these casino chips, and they are gonna generate us plenty of energy later. All right, let's jump in. So step one, oxaloacetate. That's why it's a cycle, because oxaloacetate is the last step, but it's needed to start the first one. Oxaloacetate, a compound made primarily from pyruvate, starts the TCA cycle by fusing with an acetyl-CoA. The four-carbon oxaloacetate joins with the two-carbon acetyl-CoA to make a six-carbon compound, and then we go on and on. The compound has changed a little to make a new six-carbon compound, which releases carbons as carbon dioxide, becoming a five, and then a four-carbon compound, and then just as we're traveling through here, we're releasing carbon dioxide, we're capturing electrons, capturing hydrogen ions, and we run through the cycle, and the cycle continues on and on, as long as you have acetyl-CoA and as long you have oxaloacetate. Let's see. We talked about how ATP is gonna be produced from that GTP compound. Step six, knowing that glucose produces pyruvate during glycolysis, and that oxaloacetate must be available to start the TCA cycle, you can understand why the complete oxidation of fat requires carbohydrates, so if you don't have these carbohydrate precursors, that's when this system gets overwhelmed and that's when your liver starts to make ketones. All right, so let's just review before we go to the electron transport chain. So let's review the metabolism of glucose. So glycolysis, you have a net gain of two ATP, but you also got two of those NADHs, which will be worth six ATP later. Intermediate step, where we turn pyruvate to acetyl-CoA, no ATP's produced, but we get two more of those NADHs. So now before we even started the Krebs cycle, we have a net, we've made two ATP and we have four of those electron carriers NADH. During this process, we're gonna get six more of them, so now we've made two more ATP, so we made two ATP during glycolysis, none during the intermediate step, and two here, so we've made four ATP, but now we have 10 NADHs, two from glycolysis, two from the intermediate step, and six from here. Each one of those is worth three ATP, so 10 times three is 30. So we've made four ATP, but now we've got 30 more ATP coming, and we have two FADH2s, which are each worth two ATP, so two times two is four. So now we've made four ATP, we have 30 ATP coming from NADH, plus four ATP coming from FADH2, so that's 38, so four plus 30 plus four. So the complete oxidation of glucose generates 38 ATP, but why did I say earlier that we only get 36? Well, if you were a bacteria, you would actually generate 38 ATP, but you're not, and that's because it actually, we have to spend two of those ATPs to get our energy into the mitochondria, to get our building blocks into the mitochondria. So we do make 38 ATP, like bacteria do, but we have to spend two of it in a way that they don't. So you karyotes like us, we fully oxidize glucose into 36 ATP, and prokaryotes like bacteria, would fully oxidize to 38. So that's the difference there. Okay, now we're at the electron transport chain. This is much better to see, visually see it actually happening, but I'll run through the process here. Here's the point. We've been talking about electrons the whole time, right? Electron transport, electron carriers, all of this, but what you're gonna see happen here is the electron transport chain, we've captured all these electrons that we dump in the electron transport chain, but the flow of electrons is really only needed to power the pumping of these hydrogen ions. So let me read through it. The coenzymes, which would be your NADH worth three ATP, and FADH two worth two. So the coenzymes deliver hydrogens and high energy electrons to the electron transport chain from the Krebs cycle, glycolysis, and fatty acid oxidation, okay, that's step one. So as they release their electrons, that powers this pumping. And what the pump is doing is pumping hydrogen ions outside of this inner mitochondrial membrane. So you're seeing a buildup of all these red H pluses or hydrogen ions, which are also called protons. You might hear people call these protons. If you look at the periodic table, hydrogen's the only element without a nitrogen. So hydrogen never had a nitrogen, I'm sorry, a neutron. So hydrogen never had a neutron, and then if you remove its electron, making it a positive ion, all that's left is a proton. So H plus, calling it a hydrogen ion and calling it a proton, you're saying the same thing. All right, so that's step one. Step two, passing electrons from carrier to carrier along the chain releases enough energy to pump hydrogen ions across the membrane, and that's the key. We used all these electrons to pump hydrogen ions. And then we'll see that the movement of these hydrogen ions is actually what creates energy. But step three, before we get there, oxygen accepts the electrons and combines with hydrogens to form water. So the reason, you know, your metabolism will make, I don't know, one in three quarters, somewhere in the neighborhood of two cups of water today. And that's because oxygen is called the final electron acceptor of our metabolism. So you take all these electrons, take some of these hydrogens, and you form water. So your metabolism builds water as part of one of its waste products. Again, we use it, it's a useful waste product or maybe we call it an end product. But here's the key. We moved all these hydrogen ions. So they all have the same charge and likes repel. They don't want to be by each other, right? Diffusion says that things are going to move from where there's a lot of them to where there's not. So we have this buildup of hydrogen ions that don't want to be around each other. And now they want to come back into the inner mitochondrial space here, the inner compartment, as you see here. But, your body says, or your mitochondria says, okay, you can come back in. But you have to come in through this turn style. You have to come in through this enzyme. And that enzyme is called ATP synthase. So let me read step four and then I'll put my spin on it. Hydrogen ions flow downhill from an area of high concentration to an area of low concentration, that's diffusion, through a special protein complex that powers the synthesis of ATP. Its name is ATP synthase. ACE tells us it's an enzyme that synthesizes ATP. And so as these protons, it's actually like a turn style. As these protons flow through ATP synthase, it spins. And the spinning of this protein complex, this enzyme, is what generates the energy needed to take ADP and add a third phosphate to it to generate ATP. So it's the movement of these protons that spins the ATP synthase enzyme that generates energy. So this isn't odd, right? Think about a wind turbine. The spinning of the blades of the wind turbine generates energy that can recharge these batteries. Think about a nuclear power plant is basically a steam driven turbine system, right? It's a steam driven turbine with one really dangerous room. And that dangerous room has radioactive material in it that superheats the water to generate the steam to spin the blades. Hydroelectric dams. So water flowing down these dams spins turbines to generate energy. So we see it all around us. The spinning motion can generate energy that we need. Well, that's what's happening here. Hyrogen ions or protons flow through, spin, spin, spin. That spinning generates the energy needed to turn ADP into ATP. ATP then goes and does its job, becomes ADP again, and comes back to get recharged. I know it's an oversimplification, but it's the best I can do. All right, so the K-cals or kilocalories or calories per gram secret revealed. So why is fat worth nine calories per gram? Glucose is only worth four, or carbs are only worth four because we have more hydrocarbons to work with. And also there's less oxygen. So you can cram, you can cram, look at all these oxygens over here, oxygen, oxygen, oxygen, oxygen. Then there's just one on the end. So oxygen's really big. So you can't cram as many hydrogen and carbons into a gram of carbs like you can fat. So fat is worth nine calories per gram. Carbs and protein are worth four. Alcohol is worth seven, kind of in the middle. Okay, switching gears, feasting versus fasting. So we've already mentioned a few things here, but so feasting, when you have excess energy, your metabolism favors fat formation. No doubt about it. Regardless of excess from protein, fat, or carbs, your body can turn protein, carbs, fat, or alcohol into fat. So if you have excess energy and you don't need it, so your body will use whatever protein it can to build proteins. It'll use whatever carbs it can to fill your glycogen stores and be used for fuel. It'll use fat for fuel, but then whatever's left over can become fat. That's how your body stores excess energy. All right, the fuel mix we've talked about that depends on your activity, like what kind of things you should be doing. All right, when does the body use energy? It's all the time, right? I always say your body's always eating, like your body is either digesting the food you ate a little bit ago, or it's digesting the stored energy that you ate a long time ago, right? It's digesting the donut that's been on your hips for eight years. That's, your body is always needing energy and always using it. We'll cover this more in the next chapter, but let me read this point. Cells are working all the time, even during sleep and relaxation. This represents about two thirds of your total energy expended each day. It's called your basal metabolic rate. So most of the energy that you're gonna burn today is just gonna be keeping you alive, right? If you just laid flat in your bed for 24 hours, that would be your basal metabolic rate, and it'd be about two thirds of total energy expenditure for most people. If you're an athlete training six hours a day, that percentage would be different. All right, so the transition from feasting to fasting. So after a meal, the energy in the food that you ate, the glucose and the fat are gonna be brought into your body. You're gonna use some and you're gonna store the rest. So that's gonna be in that fed state after you eat. Fasting, so fasting is when someone chooses not to eat. Starvation occurs when they have no choice. So that's the big difference, right? I mean, it's basically a starvation diet is really a fasting diet because you're choosing not to eat, you could eat. Intermittent fasting and different fasting protocols are getting very popular. Personally, I think that time-resected feeding and intermittent fasting can be really good for some people. There's nothing magic about it, but it does help some people control their caloric intake. So in the end, if you're trying to lose fat, you have to be in a caloric deficit and if a fasting protocol helps you do that, then more power two years long as you're being safe. All right, the body does not distinguish between these states. Again, your body doesn't, at the cellular level, it doesn't care if you're purposely not eating or you can't eat because there is no food. When energy is needed, your body draws on stores of fat and glycogen. So remember, you've got several hundred calories of carbs are stored in your body as glycogen in your muscles and your liver. Liver glycogen can be released into your bloodstream to help fuel your entire body. Muscle glycogen can only be used by those muscles. Body fat, we have almost an infinite storage capacity for energy is fat. One pound of fat is worth it in the ballpark of 3,500 calories. All right, so here we see feasting versus fasting, what happens? So feasting will start at the top. When a person eats in excess of energy needs, the body stores a small amount of glycogen and much larger quantities of fat. You can know why is that? You can only store so much glycogen. It's because glucose brings with it a bunch of water, so it's super heavy. Like if you were gonna be backpacking through Yellowstone, you wouldn't bring big, heavy foods, right? You wouldn't bring like, it'd be like bringing a canned soup, right? Because you have all that water in there. So you have big, heavy cans of soup, that's glycogen. You can't store very much glucose as glycogen because it's so much water in it. What would you bring? You'd bring like dehydrated packets of food that you could add water to later. And that would be, that's body fat. Body fat doesn't have all this water with it. So you can store, a pound of fat stores 3,500 calories. That's probably twice the glycogen you have stored in your entire body in a single pound of fat. So you store a little bit of glucose as glycogen. After that, you start turning things into fat. So as you see there are protein, digestive amino acids, and you're used for body proteins or turned into fat. Fat can be used for fuel or turned into fat. Carbs turned into glycogen or turned into fat. That's when you're feasting. So when you're fasting, when nutrients from a meal are no longer available to provide energy, about two to three hours after a meal, the body draws on the glycogen and fat stores for energy. So your liver glycogen should keep your blood sugar stable. Your muscle glycogen can fuel your muscles and your body fat can be the energy for most of your things that you need. Again, depending on activity. Right, if you're gonna be sprinting, then your body fat isn't gonna help you as much because you need more glucose for that. All right, C, fasting beyond glycogen depletion. So let's say you're going on a longer fast. As glycogen stores dwindle, after about 24 hours of starvation or fasting, the body begins to break down its proteins, muscle and lean tissue to amino acids to synthesize glucose needs for the brain and the nervous system energy. In addition, the liver converts fats to ketone bodies which serve as an alternative energy source for the brain, thus slowing the breakdown of body protein. So how much protein are you gonna lose if you go on a fast? That's a really important question. The real answer is how much body fat do you have, right? So the simplest way to look at it, this is based on the Minnesota semi-starvation or starvation studies that were done a long time ago, but a pound of fat can release about 30 calories of energy, right? So if you have 100 pounds of fat on your body, then that means what's 100 times 30? That your body should be able to release 3,000 calories a day of fat energy. So if you're 100 pounds overweight and you don't eat for 24 hours, you shouldn't really lose much lean tissue, if any at all, but it'd be a small, small amount. Now, if you're at 6% body fat trying to get 5% body fat and you only have a few pounds of fat on your body, then yeah, you're gonna lose a lot of lean tissue when you fast. So how much lean tissue, so you see here, body protein's broken down for fuel. How much of that actually happens depends on how much fat you have and how readily you can break down the fat for fuel. Because remember, if you're breaking down a bunch of fat for fuel, you have all that glycerol that can become glucose. So you, I mean, I get like dexa scans and I get my metabolic rate tested and all sorts of cool things because I've lost a ton of weight. And in my last two scans were six months apart and I actually lost 37 pounds of fat and gained six pounds of lean tissue by looking at the dexa scan. So if you have enough fat on your body, you can even gain lean tissue, let alone not lose it, so it depends on how long you're fasting, how big the deficit is, how much fat you have. There's lots of things that go into play here but you don't, you know, but if you're, and then other things too, like if you're exercising, if you're exercising your body will preserve muscle because it needs it, right? So if you're on a crash diet and you're already lean and you're not exercising, over half the weight you lose could be fat, could be muscle, could be lean tissue, sorry, not muscle, could be lean tissue because your organs will shrink and stuff too. If you've got plenty of fat to lose, you're exercising, you're strength training, you're being smart about your dieting, you can get to the point where you're not losing any lean tissue or losing just minuscule amounts. Now you'll lose some lean tissue, like if you lose 100 pounds, you're gonna lose some muscle because you're carrying 100 less pounds around so your muscles, you don't need as much muscle really. But again, that's a, I'll do a separate video on that one topic, it's pretty interesting. But yes, the longer you're fasting, the less fat you have on your body, the more your body will have to rely on protein as a fuel source, no doubt about that. Okay, so fasting leads to inadequate energy, glucose and fatty acids are broken down into acetyl-CoA, which enter the energy pathway. After several hours of fasting, liver glycogen depletes. As a result, blood glucose levels will drop. So that's when we rely on gluconeogenesis. So gluconeogenesis is the making of glucose from non-carbohydrates. And this is why I think that how much fat you're burning and how much glycerol you have available will determine how much amino acids need to be broken down for fuel. But that's also why if you're on a diet that's not gonna rely on carbohydrates, you should be on a moderate to higher protein intake because then your body can use those proteins for fuel too. Because another way to preserve lean mass when you're on a diet is to consume more protein. Let your body burn the proteins you're eating for fuel, not the proteins that are in your muscles. All right, adaptation, creating an alternative fuel. This is the idea of ketogenesis or ketosis or ketogenic diets. So parts of your nervous system and your red blood cells need glucose. That's why we have an RDA of 130 grams per day. So your body can, but there are alternate fuel sources. Red blood cells always need glucose. You're always gonna need some glucose, whether you're eating it or your body's making it, you need it to fuel your red blood cells. The cells of your nervous system though, they can rely on lactate and ketones and other fuel sources. That's what ketones really are. Your brain can't just burn fat for fuel like other parts of your body. So what your body does when blood glucose levels are running low, your liver says, okay, we have to feed the brain. So your liver makes ketones. Ketones go to the brain and fuel them. So that's this idea of an alternative fuel. So use fat to fuel the brain and that's what ketone bodies do. It slows the rate of body protein breakdown. Yeah, it's an alternative fuel source. I mean, I like to consider it a macronutrient. It's just one that your body makes. So since your body can burn ketones for fuel, your brain can burn ketones for fuel, it won't have to turn protein into glucose to burn for fuel. And ketosis induces appetite loss. I mean, in some people, in many people, that's why people that go on ketogenic diets, they often don't feel as hungry and that might be what leads to some of their weight loss. Okay, and then we'll cover this more in the next chapter, but adaptation, conserving energy. So if you're in a fast, if you're fasting, if you're not eating as much, if you're on a diet, then that means you're changing the calories inside of the equation. So your body will respond by changing the calories outside of the equation. You will burn less energy. So hormone levels will change. So it's maybe your thyroid hormone levels will drop and things like that. Your brain will ask you to move less and that's why you'll see a reduced energy output. The biggest change there, and we'll cover this in the next chapter, but the biggest change is in what's called neat or non-exercise activity thermogenesis. So if you're on a diet, you're just like, I just want to sit back like this. I want to rest. I want to lie down. I'm not motivated to get up and move. You ever just been motivated to get moved? Well, that's how you should feel most of the time when you have adequate fuel sources. But when you're on a diet, you're going to be less and less likely to do that. So your body's going to look for ways to reduce energy output. Your metabolic rate will drop some, but it does appear that the biggest way your body does this is by asking you not to move as much. So the biggest change, so if you go on a really strict diet, your energy expenditure is going to drop, but most of it isn't your basal metabolic rate changing. Most of it is going to be changes in non-exercise activity thermogenesis. You're going to fidget less, right? When you're moving, you're fidgeting. You're going to fidget less. You're going to want to sit more than you stand, things like that. I noticed that when I'm teaching in the classroom, I'm almost always up and moving, but when I've been on a diet for a while, I'll notice the urge to sit that I normally don't have, right? Normally I love pacing. You see, I'm even moving a lot when I sit here, but I love pacing when I'm teaching, but if I'm on a diet, my brain's like, you see a chair right there, right? Why not sit in it? So that's one of the ways that you reduce energy output. Fasting, I like this point here. Fasting supports weight loss, but the not best option for fat loss. So again, there are two separate things, right? If you want to lose fat, you have to do different things than if you want to lose weight, right? If you want to lose weight, just starve yourself, but you will lose lean tissue. If you want to lose fat, be smart about your diet, lose weight slowly, maybe half to 1% of your body weight a week, strength train as much as you can to tell your body to send signals to your body to keep your lean tissue instead of using it as fuel. All those things would be true. And then of course, if you're starving yourself, that you can be irritable and tired and super hungry of course, and all those types of things. Some people though, say fasting actually really helps them feel better. A lot of people like ketogenic diets and doing different types of fast because of mental clarity. I mean, this goes back to different religions and philosophers, all sorts of people believed in this idea. And the reason for that is if you are fasting, your brain, you will have more norepinephrine in your brain. So norepinephrine is noradrenaline or it's related to its cousin, which is adrenaline. And norepinephrine in the brain does help with focus, which sort of makes sense, right? People talk about fasting and they think you just want to curl up in a ball and die. But if you can't find food, you need to be motivated to find food or you will die. So you might see an increase in mental clarity because our hunter-gatherer ancestors would have used that state to find food or not become food, right? So it's interesting to think about, but maybe we'll do a separate video on that someday. All right, so low-carb diets, they certainly can be effective. They've been shown in studies that when you match them for calories and protein intake, they're just as effective as other diets for losing weight. There's nothing magic about them. But if, you know, one of the reasons I think low-carb diets work so well for most people is they are restrictive, right? By removing foods that have a lot of carbs, especially your process-refined carbs, you're removing a lot of junk food. And it isn't just foods that have carbs, right? If you're not eating pizza and cookies and cakes, you're not eating those carbs, but you're also not eating the fat and the calories. So that's why they seem to work. You can read some of these here, but potentially a low-fiber low-carb diet will lead to constipation. So if you're gonna be on a low-carb diet, you should still be getting fiber somewhere. They lead to a drop in blood pressure because you do actually produce more urine. That's a good thing if you have high blood pressure, though. But if you're on a low-carb diet, you should be drinking more water and you should be getting more electrolytes to make sure your fluid balance stays good. You can certainly be tired as your body adapts to a low-carb diet. It's no doubt about that. Elevated uric acid, this would be because if you're consuming more animal proteins and things like that, uric acid might go up. But it may not because one of the best ways to raise your acid in your body, not saying you want to, is consuming fructose. So if you're on a low-carb diet and you remove sugar, then you removed your biggest source of fructose as well. The change in your breath, that's ketones. So ketones, it smells like juicy fruit gum, would be how I would describe it, or some people would describe it as maybe like paint thinner or something. But it's actually ketones being lost in your breath. And then yeah, I definitely don't recommend really strict low-carb diets for people that are pregnant. I don't recommend really any alternative diets when we're pregnant, or I'm not pregnant when they're pregnant. All right, now let's check number three. Again, see if you know these. Gluconeogenesis, that's whenever you turn a non-carbohydrate into a carbohydrate. So here you see new glucose being made from amino acids, but glycerol can also make glucose. Glycogen in protein breakdown increases urine productions, or just remember when you're breaking proteins down for fuel, you have to deal with the nitrogen. That's gonna become ammonia, then become urea, then it's gonna be lost in your urine. So if you're on a higher protein diet or a ketogenic diet, you should be drinking more water. Ketones, it's an alternate fuel source so your body turns fat into ketones, so your brain can use them primarily. And glycogen is used first, no doubt. Low-carbohydrate diets reflect a similar metabolism to a fasting state, I would agree with that. Protein from body tissues can be used, are used even if protein intake from diet is sufficient. Lack of glucose and incomplete fat breakdown causes ketone formation, ketones being that fuel for the brain. Okay, we made it. Now that the lesson is over, you should have learned to identify the nutrients involved in energy metabolism and the high-energy compounds that capture the energy. We talked about that, ATP and all that. Summarize the main steps in the energy metabolism of glucose, glycerol, fatty acids and amino acids, check. Explain how in excess of any of these three, energy-yielding nutrients contributes to body fat, check, and how an inadequate intake of any of them shifts your metabolism, especially low-carb diets. Okay, a lot of stuff here, I get it. There's a lot of really good juicy things in here too, but just remember I have an entire metabolism playlist if you wanna go back through this stuff in a little bit more detail. All right, I hope this helps. Have a wonderful day. Be blessed.