 Hey everybody, Dr. O. So in this thankfully shorter video for you, we're going to talk about how we burn fat for fuel. So we've been talking about all the ways that how we fully oxidize and metabolize glucose. What about fat? So first, just, you know, fat versus carbohydrate burning for energy. What are some of the key differences? Number one, it actually takes more oxygen to metabolize carbohydrates, glucose, than it would fat. And that's because as you, as you split glucose in half and you turn those two, three carbon pyruvates into two carbon acetylcoase, you generate that carbon dioxide and you use some oxygen. As you'll see here, when we, when we beta oxidize fats, which is the fancy term for burning fat for fuel, we beta oxidize fat to make acetylcoase, doesn't require oxygen. Now we all, we have enough oxygen to do both, but the reason this is important is because if you like an exercise physiology way, if you want to determine what percent of your energy is being burned by the different macronutrients, you can actually tell by how much oxygen you bring in, how much CO2 you produce, you can tell whether you're a fat burner, carb burner, et cetera. It's called the respiratory quotient. And the respiratory quotient for carbs is one because it needs more oxygen. The respiratory quotient for protein is 0.8 and for fat is 0.7. So if you're, if you're like on a ketogenic diet and you're a fat burner, you're going to be a lot closer to that 0.7. You won't be 0.7 because you need to burn some carbs too. But if you're, if you're eating a lot of carbs and relying on them almost exclusively, you'd be closer to one. So, so clinically, that's why you could actually run one of these tests to determine if someone is more of a fat or carbohydrate burner, at least at the moment, because you can change that, right? So here we see a triglyceride or a fat. On the left side, you see the glycerol backbone. As we break this apart and digest it and consume it for energy, the glycerol backbone can actually go through glycolysis. So it will actually be able to produce energy the same way glucose would. But these three huge tails are what we care about. Now these are used are going to be 16, they can be 16, 18 carbons long. Obviously you see little dots there in the middle, they'd be a lot longer. So it's a much bigger hydrocarbon and there's a lot less oxygen here than there's in glucose. So you can cram a lot more hydrocarbons in a small space, which is why there's nine calories in a gram of fat and only four calories in a gram of carbs or protein. So let's go to the beta oxidation process. Again, I don't want to make this too complicated, but you take those long fatty acid tails and you break them off two carbons at a time. Those two carbons become acetyl-CoA, they're at the bottom of the screen. And acetyl-CoA, remember we called that the keystone of our metabolism. It enters the Krebs cycle and is used the exact same way, whether it came from glucose, fat, proteins, or alcohol. So I don't care about all the terminology here and the carnitine shuttle all, it's kind of interesting. But in the end, just remember beta oxidation is how we metabolize fat for fuel. You break off the two carbons at a time and they become acetyl-CoA and then metabolize the same way glucose would be. Now, the key to note here, though, is that you can get a lot of energy from fat, right? Pound per pound, unit mass per unit mass, you can get twice as much energy from fat as carbohydrates, but this process is kind of slow. So the more quickly you need energy, the more your body's gonna rely on glucose. If you have, so I was thinking about like a fire. Fat would be these huge logs. You're gonna get a lot of fuel, but how do you start it? How do you get it lit? Carbohydrates would be the kindling. You're gonna burn through them very quickly, but you can get energy right away. So that's why I like to look at it that way. So as far as I say, fat is your primary fuel at rest or during moderate activity, which means you can comfortably hold a conversation. Glucose needs to be your primary fuel from moderate to intense physical activity. So lots of variables there, but just come in, just want to look at it. Beta oxidation, great way to get lots of energy, but kind of slow. And that's where glucose is still your primary fuel when you need energy right now. All right, so that is the real basics of the beta oxidation of fatty acids for fuel. I hope this helps. Have a wonderful day, be blessed.