 Hey, everybody. Dr. O here. Welcome to part two of the fat loss sweet spot series. So in part one, I explained why it's so important to preserve as much lean mass and muscle as possible while you're losing fat or even trying to build more of it. But now it's time to learn how to do just that. So let's start with number one in finding your fat loss sweet spot, finding the best calorie deficit. Now, these are not in order of importance. They're all critically important, but I have to start somewhere. Plus, though, I do think that this is the best place to start because the rest of the things on this list aren't near as crucial until you get lean enough to really put your lean mass at risk. They're always important, but they are much more important as you get close to your goal weight. So that's why we're starting here. So what does it actually mean to find the best calorie deficit? It's don't diet too aggressively, but what is too aggressively? You can diet a lot more aggressively if you have 100 pounds of fat to lose than if you have 20 pounds of fat to lose. The little things don't really become the huge things until you get closer to your goal. The real question is in the situation you're in right now, how aggressively can you be on your diet before you start to lose lean mass? That's going to be different for everybody. Let's look at this study. I really want to dive in. This is a neat one. It's an older one, but it's still a really, really neat one. What does the science say here? Differences in fat, carbohydrate, and protein metabolism between lean and obese subjects undergoing total starvation. This review was based on starvation studies, but it shows us what happens when someone diets more aggressively than their body and their body fat can handle. Here's the first key takeaway. Fat becomes the major source of energy for everyone during starvation, but it accounts for 94% of the energy burned in an obese subject versus 78% of the energy burned in lean subjects. So where does the rest of this energy come from in lean people? Well, you probably guessed that it comes from their lean mass. So during starvation, lean people lose two to three times more protein than obese subjects. Why? Because they use two to three times more protein as a fuel source. So lean people, they actually will use two to four times as much protein to make glucose in a process called gluconeogenesis, which means the creation of new glucose. Anytime you turn a non-carbohydrate into glucose, it's called gluconeogenesis. So lean subjects are going to be turning a lot of protein into glucose because they're only burning 78% of their energy as fat for fuel. But since obese subjects are burning a lot more fat for fuel, 94%, they're going to have a lot more of this glycerol left over. So the fat that we burn for fuel is typically, they're called triglycerides. You see up here on the screen, you have the three fatty acid tails and then a glycerol backbone, that structure on the left side there. So as you burn or oxidize the fatty acids, that tail gets left behind and you see at the bottom of that image that glycerol can be used for glycolysis to produce energy directly or it can be used to create glucose in a process called gluconeogenesis. This means that obese subjects can turn more glycerol into glucose, which means that they can meet their glucose needs while using a lot less protein for fuel. This is actually another way that fat can be turned into fuel. So this is an advantage that someone that's obese and burning more fat would have. So long story short, protein turnover is increased in the lean subjects, but not the obese subjects. And I think I've kind of explained why, since obese subjects are burning so much more fat for fuel. So here's an actual quote from this study, although obese individuals have more body protein and fat free tissue than lean individuals, they lose these components at a slower rate during prolonged starvation than lean individuals, meaning if you have a lot of body fat for fuel, you can be more aggressive than if you don't. That's the point I'm trying to make. Another really important thing that I pulled out of this study, leucine. So leucine is an amino acid. It's the most important amino acid for stimulating muscle protein synthesis. Basically you need to reach a leucine threshold with your meals if you want to maximize muscle protein synthesis. So just remember leucine, very important amino acid. Leucine oxidation increased by 230% after a 60-hour fast in lean subjects. It only increased 17% in obese subjects. So a 230% increase in burning or oxidizing leucine for fuel in lean subjects versus 17%, really just a trivial amount in obese subjects, after a 60-hour fast. So this is a big problem for lean subjects because we don't want to be burning leucine for fuel. We want to be using it to build or maintain muscle. So this is also why a 60-hour fast would be much safer for someone with 100 pounds to lose than someone with 20 pounds to lose. I'll talk about how I transitioned to a less aggressive calorie deficit as I got leaner in the next video. But yeah, if you're trying to lose 20 pounds, a 60-hour fast is going to have a much different impact on your body than it did for me when I first started at 414 pounds. Same study. It is no longer acceptable to describe the metabolic response to starvation as a single typical response. So long story short, you can be much more aggressive if you have a lot of fat to lose. The little things don't become the big things until you get pretty lean and get pretty close to your goal, those last 20 pounds especially. All right, let's switch studies then. So how do we actually know, right? When do we know we really have to start to worry about losing lean mass? I think this is the study that gives us the answer and it's one of my favorite studies to talk about. So a limit on the energy transfer rate from the human fat store in hypophagia. This is one of the most important studies that I've ever read as a dieter and I've shared it in other places as well. You have to know how much energy your body fat can provide if you want to know how aggressive you can be on a diet. So let me read this quote and then I'll make sense of it for you. A limit on the maximum energy transfer rate from the human fat store in hypophagia under eating is deduced from experimental data of underfed subjects maintaining moderate activity levels and is found to have a value of 290 plus or minus 25 kilojoules per kilogram per day. This ends up being between 29 and 34 calories per pound of fat. So I usually stick with 30 calories as my guide. So next part of the quote, a dietary restriction which exceeds the limited capability of the fat store to compensate for the energy deficiency results in an immediate decrease in fat free mass. In cases of a less severe dietary deficiency, the fat free mass will not be depleted. So if you know how much body fat you have, you know how many calories it can provide. If you diet more aggressively than that, you will see an immediate decrease in fat free mass. If you stay in that safe zone where you're burning your body fat stores, but don't dip underneath there, you will you will preserve your fat free mass. That's why I love this study so much. It gives us the calculations, right? This information can be a huge game changer. You no longer have to guess how many calories you should be eating on a diet. So I won't go through all the math again here because I've covered it in great detail in these videos and you can you can see those. But here's the big picture. The lesson from this study is that every pound of fat on your body can provide about 30 calories per day, right? This explains why you can be so much more aggressive on a diet when you have a hundred pounds of fat versus 20 pounds of fat, right? A hundred pounds of fat can provide 3,000 calories per day. 60 pounds of fat can provide 1,800 calories per day. And 20 pounds of fat can provide only 600 calories per day. So let's look at those numbers. Do you see why someone that burns 2000 calories per day can be as aggressive as they want at the beginning of their weight loss journey? If they have a hundred pounds of fat to lose, but they have to become less aggressive in the middle and then they have to be much less aggressive at the end, right? No matter how much fat you have on your body, you've got to come up with these 2000 calories. So where are the 2000 calories going to come from if they can't come from your body fat? It either either has to come from the food you're eating or from lean mass and my vote is food, right? This is why there is no one size fits all approach for intermittent fasting or any way to get into a calorie deficit. My entire program is designed around helping you take a science driven approach to weight loss that changes as you do because the amount of fat on your body is going to change, right? So be sure to check out these other videos for the details. And then also you can check out these videos if you don't know how much fat you have on your body or how many calories you burn today. There's lots of great ways to determine those things, but these will get you pointed in the right direction. All right. So number one, finding the best calorie deficit, right? Every situation is unique, but science can give us the clues for a good place to start, right? This is great news. We are now one step closer to finding our fat loss sweet spot, right? So we can determine how many calories do I need to eat? How big can my deficit be before I start to lose lean mass? And then we can live there. We can live in that fat loss sweet spot. So we'll cover, we'll cover how to determine if you're dieting too aggressively by looking at the best rate of weight loss in part three. I hope this helps. I'll see you in the next one. Have a wonderful day. Be blessed.