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Why is it that some people seem to eat whatever they want without putting on any body fat? Almost all of us know that person that just doesn’t put on body fat no matter how much they eat.

And if you search the internet for 10,000 calorie challenges or #cheatday, you’ll see plenty of very fit folks eating huge amounts of food, without any body fat to show for it.

What gives?

While it seems like these people have some innate ability to eat without consequence, their bodies follow the same physiological rules as everyone else’s. The real explanation boils down to their eating and exercise habits, including the ones you don’t see. 

In this podcast, I’ll answer why some people seem to be able to eat as much as they want without getting fatter. Press play and let me know what you think!


0:00 –  Try Whey+ risk-free today! Go to and use coupon code MUSCLE to save 20% or get double reward points!

4:20 – How can people eat whatever they want without gaining weight? 

10:49 – Burning calories through digesting food

13:52 – Storing macronutrients as fat

20:07 – Moving more when you eat more

21:48 – Calorie absorption  

Mentioned on the Show:

Try Whey+ risk-free today! Go to and use coupon code MUSCLE to save 20% or get double reward points!

What did you think of this episode? Have anything else to share? Let me know in the comments below!


Hey there, I’m Mike Matthews. This is Muscle for Life. Thank you. Thank you for joining me today. Now, if you Google or maybe not Google, right? How about search? Preferably not on Google, the 10,000 Calorie Challenge, or if you go on just about any social media network and look up the Cheat Day hashtag, you’ll find.

A lot of examples of very fit people eating ungodly amounts of food without having any body fat to show for it. Some of these people seem to do this fairly often too, and stay very, very lean. And we’ve all known, at least one person who seemed to be able to put away platters of food without putting on any weight.

So what gives, are these people just blessed with the right genes? Do they have an abnormally. Fast metabolism. No and no because while it seems like these people are simply immune to gaining weight, no matter what they do, no matter what they eat, no matter how much they eat, their bodies do follow the same physiological rules as yours.

They too are subject to energy balance, and what that means then is the real explanation for their apparent freedom. From fat gain is unsexy. It boils down to their eating and exercise habits, including ones you don’t see. And that is crucial. Not some inborn trait that just allows them to gorge with impunity, and that’s what this podcast is going to be about.

Why can some people seem to be able to eat so much without getting fatter before we weighed into it? One of the easiest ways to increase muscle and strength gain is to eat enough protein and to eat enough high quality protein. Now, you can do that with food, of course, you can get all of the protein you need from food, but many people supplement with whey protein because it is convenient and it’s tasty, and that makes it easier to just eat enough protein, and it’s also rich in essential amino acids, which are crucial for muscle building.

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All right. Let’s start this discussion with an overview of what is going on here. There are three basic reasons why some people can apparently eat whatever they want without gaining weight. The first one is you probably aren’t seeing these people at all times, and you’re probably not carefully measuring their calorie intake, and it’s likely that their average.

Calorie intake is less than you think. Another common reason is you’re not seeing these people’s activity or exercise habits, and many times they are exercising or are just moving around a lot more than you realize. And finally we have that while overeating for a few days, or even a few weeks, will almost always cause some fat gain.

There are some changes that occur in your body that can prevent all of the excess calories you eat from being stored as body fat. And often these people are benefiting from this as well. Now those first two points are pretty straightforward. People see someone regularly eating large amounts of food without gaining fat, and they assume that this is due to some biological blessing, like a fast metabolism.

I’ve had many people ask me if that’s how I can eat a bunch of dessert and not be fat, or how I can eat a a few plates of food at Thanksgiving and still be lean. People assume that I do that. A lot more often than I actually do. And so then the mistake there is basing an assessment on just a snapshot or maybe a few snapshots of somebody’s daily routine.

So maybe it’s a coworker or it’s a classmate who eats these big lunches, or it’s a friend who gluts themselves at the holiday parties, or a roommate who always seems to be snacking throughout the day. In reality though, many of these people, they don’t eat as many calories as you might think. It looks like they eat more than they do because they eat less the rest of the time when you’re not seeing them eat large amounts of food.

So for example, the friend who seems to go hog wild at lunch might not eat breakfast at all, or maybe they have a very light dinner or. The roommate who always has a snack in their hand. Maybe they rarely eat large meals or sit down meals. Maybe they just mostly snack and the party binge. Well, they probably eat smaller portions the rest of the time when they’re not going hog wild.

And the scientific term for this gap in your knowledge, is known as selection bias, and it affects all of us. If you’re human, you have to deal with selection bias, just like you have to deal with confirmation bias and many other biases that psychologists have identified. So when you see Skinny Dave devouring that entire pizza on a New Year’s Eve, and you think.

How does he eat so much and look like that, but then you fail to notice that, well, he actually eats a lot less the rest of the week. Or maybe you notice Lean Lisa munching on some fruit nuts all day, but you don’t realize that she doesn’t eat a breakfast or a lunch or a dinner proper. She just has. 6, 7, 8 smaller little snack meals throughout the day.

And this same principle applies to activity levels too, because while some people do eat considerably more than others without gaining weight, And sometimes it’s others who weigh more, who should be able to eat more without gaining weight. So that can really throw people for a loop. When you have smaller people eating more than bigger people eating and not gaining weight, and if the bigger person were to eat the same amount as the smaller person, the bigger person gains weight.

So one way that can happen is activity levels. So someone who lifts weights two or three times a week and let’s say walks their dog a few laps around the block every day. They don’t need to eat nearly as much as somebody who is hitting the gym five days per week and participating in something like Brazilian Jiujitsu maybe, or boxing.

Or maybe they go rucking or they go hiking or cycling on the weekends. A lot of energy expenditure. Most people who eat a lot, who eat quite a bit more than average without gaining fat don’t have some special metabolic advantage. They are just probably eating about as many calories as they are burning over time.

If you were to average out their daily calorie expenditure, And their daily calorie intake, or if you were to look at it on a weekly basis, the average number of calories burned versus eaten per week, you would see that there is a parody there. And so then what many people do is they overestimate their calorie intake or underestimate their activity levels.

They think they’re eating four, 5,000 calories per day. And um, I don’t wanna mix up the days here, so this is someone. Observing this person who can eat a lot of food and stay lean, so this person observing might think, wow, they’re eating four or 5,000 calories per day. Or maybe the person themselves who is able to stay lean on a lot of food, they might think they’re eating four to 5,000 calories per day.

But in reality, it’s more like maybe 3000 on average. And then the activity, uh, energy expenditure might be underestimated. The person, again, themselves, who just stays lean, they might think that they burn, oh, I don’t know, maybe a thousand calories per day when it’s more like 2000 calories per day. Now, with all of that said, There are a few quirks of human physiology that prevent all of the calories that we eat from being stored as body fat.

And this partially explains why the aftermath of overeating isn’t as severe as we sometimes think or expect. And the main factors in play here are the calories. Burned during the digestion of food, the storing of some macronutrients as fat more easily than others. The increase in physical activity in movement that can occur when you eat more and the absorption of the food, you don’t necessarily absorb every calorie.

You eat. So let’s look at each of those things in more detail. Let’s talk about burning calories through digesting food. Now, when you eat a meal, your body has to burn energy to digest and process the food, and this is known as the thermic effect of food. And research shows that it accounts for approximately 10% of your total daily energy expenditure that is about one in 10 calories.

That you consume is burned during digestion. Now how much energy you burn through T E F depends on the size and composition of a meal. Smaller meals require less energy to digest, of course, so they also cause a smaller increase in energy expenditure. Larger meals, on the other hand, require more energy to digest, and so they cause a greater rise in energy expenditure.

And this is also part of why you feel warmer. After eating a large meal, like for me, if I eat a big bowl of pasta and I am in a room that is maybe around 72 to 75 degrees, there’s a fair chance I will start sweating and that’s, that’s my body expending energy to turn that food into usable. Energy, turning those calories into things that the cells can use and that can be stored into body fat and so forth.

Now, studies show that the thermic effect of protein, carbs, and fat is quite different. Protein has the highest T E F score of around 20 to 30% carbs, around five to 10% in fat, around zero to 3%. Now, what that means is meals higher in protein and carbs cause a greater increase. In energy expenditure, the thermic effect is higher than meals high in fat, and how processed or unprocessed your food is also changes its effect on t e F.

In one study conducted by scientists at Pomona College, they found a processed food meal of white bread and American cheese increased t E F about 10%, whereas a whole food meal of multi-grain bread and cheddar cheese increased t e f about. 20%. And another study found similar results when people burned about 92 extra calories per day by eating whole grains instead of refined grains.

Now, it was over the course of about six weeks, and so let’s say that you. Overeat by a thousand calories, you burn 2000 calories in a day and you eat 3000 calories. Well, right off the bat, you’re losing about a hundred of those excess calories to the thermic effect of food. And that’s just an across the board average though, if we look at.

What you ate. Let’s say the meal that contributed the extra 1000 calories. Let’s just keep it simple. It’s one meal and it was high in protein and high in carbs or one of the other, and it was mostly composed of Whole Foods. Well, then you might be burning closer to 150 or 200 or maybe even upward of 250 of those calories off right away.

Now let’s talk about storing some macronutrients as fat more easily than others, because how many calories you store as body fat does depend on what percentage of those calories come from protein, carbs, or fat. And this is because those macronutrients are not all processed in the same way by the body.

Protein is used almost entirely for repairing, building and regenerating cells, hormones, and other molecules in the body. And excess protein, excess calories from protein are burned off as fuel in the liver. Protein is never directly converted into body fat. There is no mechanism for the body to do that.

Now if you look at carbs, those are mostly stored in the muscles and the liver in the form of glycogen. Many people are surprised to learn that while the body can turn glucose, which of course is obtained from carbs into body fat, it doesn’t happen under normal circumstances. Research shows that you have to eat a lot.

Of carbs for a fair amount of time. I’m talking 1000 plus grams of carbs per day for maybe six, seven plus days in a row. Then you might see a considerable rise in what is known as de novo lipogenesis in the process that turns the excess. Carbs, the excess glucose into body fat. But under normal circumstances, carbs are rarely converted directly into body fat.

Now that leaves us with dietary fat, and this is chemically very similar to body fat and thus your body prefers to store dietary fat as body fat. And then burn carbs and protein for immediate energy. Now, you might be thinking that if I’m right, can’t you just outsmart your body’s metabolism? Can’t you hack your metabolism by eating a ton of carbs and a ton of protein and keeping your fat intake really, really low?

Unfortunately, that’s not as effective as I wish it were. It would be fun, right? Because if you eat too many carbs, let’s just talk about that first. You will gain fat. Now, chemically speaking, carbs are very different from the molecules that make up body fat from triglycerides, and they have to undergo an energy intensive process to turn into those molecules that I mentioned earlier called de novo lipogenesis.

Now, if you ate, say a moderate, even a high carb diet with a moderate. Normal amount of dietary fat. There would be little or no de novo lipogenesis happening in your body. But if you started to eat at a lot of carbs, like I mentioned, there would be de novo lipogenesis happening, and that would contribute to your body fat levels and it could contribute considerably, even if 15 to 25% of the energy in the carbs is lost during the process of converting them into fat.

So maybe a a hundred calories worth of carbs might only turn into, call it 75 or 85 calories worth of body fat, but it will get converted into body fat and overeating. Carbs can contribute to fat storage in another way too, because as your body burns more and more carbs for energy, which it will, of course, if you are feeding it a ton of carbohydrate, it will burn proportionally less of the fat you eat.

Thus, more of the dietary fat that you’re eating will be stored as body fat. And so what that means then is the more carbs you eat, the more fat you will store and the less you will burn throughout the day. And those carbs can directly contribute to fat gain through de novo Lipogenesis. And this is why most studies show that people gain similar amounts of body fat after overeating carbs or fat.

And just to make this. Point clear because it’s important. If you are eating a high fat diet, you are going to burn more fat for energy. Your body’s going to have to do that. Let’s say you are eating a really high fat diet and really low carb diet, but you are also going to store fat, more dietary fat as body fat.

Now if you flip that around, And you are eating a, a very high carb diet, low fat diet. Some of the carbs are going to be converted into body fat. If you are eating really a lot of carbs for several days at a time, and, and this is, this is more relevant probably to most people eating high carb diets. I don’t come across too many people eating very high carb.

I mean 700 to a thousand plus grams per day, but maybe 500, 600, maybe even 700. That is about as high as most people go eating that amount of carbohydrate. It means that most, if not all, essentially of the dietary fat being eaten is being stored as body fat. Now protein is a little bit more interesting because there is research that suggests that excess calories from protein alone does not contribute meaningfully to fat storage in the same way, at least that carbohydrate and dietary fat can.

But let’s remember that the body does turn at least a a percentage of excess amino acids from protein into glucose, which of course then can be turned into body fat. And so again, just eating protein, that would not be a metabolic hack. Either, unfortunately, and let’s also keep in mind that most people who might want to eat large amounts of protein are not talking about carbohydrate and fat-free protein.

They’re often talking about delicious meat, for example, which is fatty meat, and they’re talking about high protein yogurt, which has fat and carbs, and they’re talking about. Eggs, which of course has fat as well, and there’s nothing wrong with eating those foods, but if you ate too much of those foods, you will get fatter.

Now, what is true though is if you are willing to keep your food. Fat intake low, you can minimize fat gain by primarily overeating, carbs and protein. And I’ll talk a little bit more about that in a moment. But for now, I wanna move on to the next point here, which is moving more when you eat more. And this one is very related to the idea that some people have naturally fast metabolisms and can just eat more than others without gaining as much weight.

It is not though. Because of Metabolic Voodoo, it is not because they are blessed with better fat burning genes. Instead, the reason some of these people seem to have fast metabolisms is just their activity levels and how their activity levels change when they overeat, because research shows that some people will spontaneously and subconsciously move more throughout the day when they overeat and that increase in activity.

Can be significant. In some studies it can be up to 700, even a thousand plus calories per day. And keep in mind that is not formal exercise. There’s actually a term for it, non-exercise activity thermogenesis or neat. And so if you take those people who are just the high neat type and you feed them an extra 1000 calories per day, some will burn off two thirds or three quarters, or even all of it.

Just by moving around more fidgeting, tapping their legs, pacing, uh, taking the stairs instead of the elevator parking a little bit further away rather than a little bit closer. And what is interesting about Neat is it varies a great deal from person to person. So when some people overeat, they move around a lot more just randomly than others.

We also know that women tend to have a smaller rise in meat than men when overeating, which is not surprising. Given their smaller statures. Okay. The final point here is calorie absorption, because you don’t absorb every calorie you eat, and you might have noticed something before, after a trip to the bathroom.

Not everything you ate was entirely digested. Some foods, particularly ones high in fiber like grains, nuts, seeds, and vegetables can make their way through us without being completely broken down. What’s more, these high fiber foods can also interfere with the absorption of dietary fat, meaning more of the fat that can be easily turned into body fat gets excreted.

Now, does that mean that many of those extra cheat day calories are just going in one hole and out the other? No, unfortunately not. The body is very good at extracting calories out of the food that we eat, and roughly 95% of the calories we put in our mouths are absorbed during digestion. That said, eating more or less of certain foods can change how many calories are absorbed, specifically eating more fiber rich foods.

Particularly those high and soluble fiber can reduce slightly how many calories are absorbed during digestion. So for example, you only absorb about 70% of the calories in whole almonds because of the fibrous shell of the almonds. That prevents a lot of the fat from being absorbed during digestion. And when you eat high fiber foods like almonds with other high fat foods, the fiber from the almonds reduces the total fat absorption of the entire.

Meal. Thus, eating high fiber foods reduces the absorption of calories from all of the foods that you eat, not just the high fiber ones. And what are the best sources of fiber? What are the best high fiber foods? Oh, that’s right. It’s fruits, it’s vegetables, it’s whole grains. It’s nuts, it’s seeds, it’s legumes.

It’s all of the stuff that our moms told us to eat. Yet another reason to get most of our calories from relatively unprocessed, highly nutritious whole foods that we have to prepare ourselves. Well, I hope you liked this episode. I hope you found it helpful, and if you did subscribe to the show because it makes sure that you don’t miss new episodes.

And it also helps me because it increases the rankings of the show a little bit, which of course then makes it a little bit more easily found by other people who may like it just as much as you. And if you didn’t like something about this episode or about the show in general, or if you have. Uh, ideas or suggestions or just feedback to share.

Shoot me an email, mike muscle for, muscle f o r and let me know what I could do better or just, uh, what your thoughts are about maybe what you’d like to see me do in the future. I read everything myself. I’m always looking for new ideas and constructive feedback. So thanks again for listening to this episode, and I hope to hear from you soon.

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