Is It Really Just Calories In, Calories Out? Metabolism, Insulin, Hormones and Why Counting Fails

0:00Jordan Feigenbaum:Calories in, calories out is real. Calorie is a unit the same way that a second is a unit and an inch is a unit. And you can no more argue that calories in, calories out isn't real than you can argue that an inch is shorter than it is. That part is settled. The people who tell you that it's not really about calories are usually on to something real, but they draw the wrong conclusion from it. Now last episode, we went after willpower and we said something that made a lot of you mad. We said that the equation is true and close to useless as advice because your body defends its weight below your awareness.

0:29Jordan Feigenbaum:and telling someone to just eat less and move more is like reading them the final score and calling it a game plan. A lot of you nodded along and plenty of you wrote back with the opposite complaint. You didn't think that the equation was useless. You thought it was wrong. It's not calories. You said, it's my insulin, my thyroid, my cortisol, my wrecked metabolism. It's the kind of food, not the amount. So today we're gonna take that seriously and we put every one of those on the table and test it. You know the guy that I'm talking about. He's in the comments under every before and after photo.

0:57Jordan Feigenbaum:He's done his own research. and he already knows that, for a fact, your weight has nothing to do with how much you eat. We're going to keep running into him today, because the thing about that guy is that he's not stupid, and he's not entirely wrong. He's just wrong about the exact part that he's loudest about. Here's the whole episode in a sentence so you can hold on to it the entire way through. Every one of these theories is pointing at something real, and every one of them turns out to be a hand on one of the levers that moves the calories in or the calories out. Sometimes both. Not one of them, though, is a hole in the equation.

1:28I'm Dr. Jordan Feigenbaum, and this is the Barbell Medicine Podcast.

1:42By the end of this, you'll be able to take any it's not calories, it's blank, and sort it out in about 10 seconds flat. Real or oversold, and which lever it's pulling.

1:51Jordan Feigenbaum:And I'm going to leave you with one thing that should end the insulin argument for good. There's a class of drug, the one that it feels like everyone you know is on right now, that works partly by prompting your pancreas to release more insulin. And despite that, it produces the biggest weight loss of any obesity drug we've ever approved. Keep that one in mind because we're going to keep coming back to it. Now the law underneath all of this is just thermodynamics. The change in the energy you've got stored equals the energy you take in, minus the energy that you burn. You don't gain weight without an energy surplus, and you don't lose weight without an energy deficit or calorie deficit.

2:25And here's what gets lost with all the shouting. The low-carb researchers agree with that. David Ludwig agrees with that. Gary Taubes agrees with it. Nobody credible in this fight is arguing with the first law of thermodynamics. They're arguing about what sets the two sides of it, which is a completely different argument. And the two sides are not simple numbers. Take the burn side, the thing that people call their metabolism. You probably picture a single number you could look up like your height. It's really three things stacked together. Most of it, roughly 60%, is just the cost of being alive, running your heart, your brain, your kidneys, keeping you at a normal temperature, all of it just to keep the lights on while you sit there and do nothing.

3:04Then about 10 % is the energy it takes to digest the food that you eat. And the last 30 % or so is movement. And most of that movement isn't the gym. It's all incidental, shifting and pacing, twitching, fidgeting, standing, and doing all of that all day. And it turns that dial up or down without asking your permission. Now that last little piece is important. The part where your body adjusts the burn on its own without telling you, because it comes back in about five minutes and it does a lot of work. And this is the whole reason for the episode. Both sides of the equation, the in and the out, are outputs of a control system.

3:38They aren't knobs that you set by hand. Last episode, we drew one conclusion out of that. Willpower is a weak lever for weight loss. And today we're gonna draw a different one. Every single it's not calories theory that you've ever heard is a claim about that control system, and every one of them lives inside the equation, not outside of it. So let's take the four big ones, roughly in the order that you hear them the most, starting with the one about the burn. The first claim, the burn side is broken. My metabolism crashed, so the math doesn't apply to me. Now there are two versions of this, and the data say they're mostly wrong, and the correct version is more useful than the myth anyway.

4:15Version one is that your metabolism falls off a cliff when you hit 40, present company included. Everybody believes this. Your metabolism didn't get the memo, though. There's a study from 2021 published in Science that pooled the best measurements we have on more than 6 ,000 people aged 8 days old to 95 years old. They used doubly labeled water, which is the gold standard for measuring how many calories you actually burn out in the real world, not hooked up to a machine in the lab. Here's how it works. You drink water that's tagged with a harmless traceable marker and then they measure how fast you flush that marker back out.

4:50The faster you clear it, the more energy you're burning. You can picture watching dyed water drain out of a tank and then timing it. Adjust for body size and here's what they found. Your burn is pretty much flat from age 20 to age 60. Not slowly declining, flat. It doesn't even start to drop until about 63 and when it finally does, it goes down less than 1 % a year. Pregnancy doesn't spike it. Your 40s didn't tank it. But there is a caveat. This is a lot of different people measured at different ages. Not the same person tracked for 40 years straight. But it is an enormous, consistent picture and there's no cliff in it anywhere near midlife.

5:27The metabolism you're blaming, or somebody else is blaming, is running about the same as it did when you were in your 20s. Now version 2 of this story is the serious one because this one's real. When you lose weight, your metabolism does go down by more than the smaller body accounts for. We talked about that in the last episode, so I'm not going to do it again. But what I want to do is put a real number on it because the number is exactly where people go off the rails. In an ordinary person who loses about 10 % of their body weight, the drop in their resting burn or calorie expenditure, beyond what you've already predicted from just carrying around less body mass, runs somewhere around 70 to 130 calories a day.

6:06Researchers had people cut their food in half for three weeks. They lost about six kilos. The resting burn dropped 260 calories a day on average, which sounds enormous. But when the researchers backed out the part that was due to simply having a smaller body to run, the true extra adaptation, the part that's actually your metabolism slowing down, was about 72 calories a day. You've probably heard a much scarier number than that. 300, 400 calories a day. Now that's real too, but it's not what you think. 85 to 90 % of that bigger number isn't your organs powering down or your body suddenly set shifting to produce less of a demand on your metabolism.

6:47It's that you move more efficiently. After you lose weight, your muscles do the same amount of work for about 20 % less energy. So the adaptation is mostly about how you move. Your resting metabolism is close to unchanged. And this next one sets up the rest of the episode. There's a study where women ate a thousand calories a day and lost less than half the weight the math said that they should. Sounds like proof that metabolism has cheated them. But when researchers took the gap apart, only about a third of it was metabolic adaptation. Half of it was that they ate more than what they wrote down.

7:19The metabolism took the blame for what the food diary was hiding. So let's put this whole thing together. Adaptation is real. It's also bounded. It's a couple hundred calories at the far extreme. Most of that is just efficient movement. And it never once flips the sign of the equation. Nobody in any of these studies ate in a deficit and gained fat. Your metabolism is not the reason that the math stopped working for you because it didn't stop working at all. Our guy in the comments has already moved on, by the way. He's done blaming metabolism and now he's on to hormones. Okay, the second claim.

7:51But it's really four wrapped into one. It's my thyroid hormone, cortisol, PCOS, now renamed PMOS, or it's menopause. Now, every one of these has real physiology, but not one of them is why somebody is carrying around an extra 40 pounds. Well, at least not due to the hormones. Let's take them one at a time because the details matter. Thyroid first because it's the most common one and there's a twist in it that most people haven't ever heard about. A genuinely underactive thyroid, real hypothyroidism, does lower your metabolic rate. That part's true. But most of the weight it puts on is water weight, not fat mass.

8:26When your thyroid hormone drops, your tissues start accumulating these big water-hungry molecules. And at the same time, your kidneys get worse at clearing free water, so you retain salt and fluid all over. That waterlogged state has a name, and it's called myxedema at an extreme. So when you finally treat the thyroid, most of the weight that comes off is you letting go of that water. And we can measure this directly. In one study, they treated hypothyroid patients for a full year, and on average they lost about four kilos. Then they measured where those four kilos came from. Essentially all of it was from water, it was just lean mass, and fat mass barely moved.

9:01In a bigger real world study, 100 patients started on thyroid medication, the median weight change was negative one 10th of one kilogram, basically zero. Half of them didn't lose anything at all. Even the American Thyroid Association says it flatly on their own patient page. Most of the weight gained in low thyroid is retained salt and water. usually in the range of 5 to 10 pounds. And treating it brings you back to the weight you were before, not to some lower number. So a real thyroid problem can add you a few pounds, but most of it's fluid. It doesn't build obesity, and fixing it corrects the water, not really the calorie math.

9:36Cortisol is next, the stress hormone, which the internet is absolutely certain is quietly making everyone fat. In people who don't have Cushing syndrome, which is a fortunately rare and genuinely dramatic disease of far too much cortisol, the everyday version of this claim is weak and it may even run partly backwards. The biggest analysis we have pooled long-term cortisol measured in people's hair across more than 26 ,000 subjects and the correlation at body mass index came out at about one-tenth. Let me translate that because a correlation of 0.1 means nothing on its own. It means that cortisol explained roughly 1 % of why people differ in body size.

10:131%. And blood and urine cortisol did even less than that. In a study of 369 people with obesity, their 24-hour urine cortisol had basically no relationship with their weight. And the authors wrote, in plain language, that the data doesn't support a strong link. Now there is a real kernel in the cortisol story, and I want to be fair to it because it's not nothing. Fat tissue carries an enzyme that can regenerate active cortisol locally, right inside the fat itself. So the level in your blood can look normal while the level in the tissue is higher. That's a real mechanism. But when researchers went and measured whether belly fat, really visceral adipose tissue, that fat around your internal organs, when that actually dumps enough of the cortisol back into the bloodstream to matter, well, in living people, that doesn't really pan out.

10:58And here's the causation trap that really puts a nice bow on this. People carrying more fat clear cortisol out of their system faster, so their bodies produce more of it just to keep the blood level normal, which means high cortisol output can be a consequence of the fat, not the cause of it. So cortisol is real, its effect on your weight is tiny and inconsistent, and if anything, the arrow may point at least partly the other way. The third one, PCOS, and actually if you haven't heard, as of this year, it's got a new name. This past May, an international consensus in The Lancet renamed it, Polycystic Ovarian Syndrome, PCOS, has become PMOS, Polyendocrine Metabolic Ovarian Syndrome.

11:36Because the cysts were never actually cysts, and the condition was never really just about the ovary. It's the exact same move the liver people made when fatty liver disease got rebranded as MASLD. So PMOS? Let's run with it. Does it break the equation? Short answer, no. But the details here are worth getting right. The best data show that women with PMOS have a resting burn about 10 % lower for every kilogram of lean tissue that they carry. 10 % lower. That sounds like a broken metabolism, and that's how it kind of gets sold, but there's a catch. Their total resting burn, the actual number of calories they burn at rest, came out about the same as everyone else's.

12:14The 10 % per kilo difference washes out once you look at the whole body. And the cleanest test settles it cold. Take women with PMOS and women without it. Put them on the same diet with the same resources and support, and 12 weeks later, they'd lost 18.5 kilos versus 19.5. Statistically the same. So the difficulty in PMOS is real, and it lives on the input side. More appetite, more cravings, insulin resistance that shows up even in lean women with the condition. The physiology makes it harder to eat less, but it doesn't make it impossible to lose weight. And I'll be pretty straight about the fashionable version of this.

12:50The one that says their fullness hormones are all broken. The studies genuinely disagree with each other. Some find the hunger hormones are higher, some find them lower, and some find no difference at all. The part that holds up is that the appetite burden is really persistent. It's not a magic hormonal off switch. Fourth, menopause. We just did a whole four-part series on this, and this particular topic is covered in episode three, so we'll just cover the highlights here. Here's the single thing you need to know for today. The best study we have followed about 3 ,000 women across their actual menopause transition with yearly body scans for over a decade.

13:24Menopause itself, the hormonal change on its own, added about one and a half kilos of body fat over the three and a half years around the final menstrual period. One and a half kilos. Meanwhile, the average woman gains 10 to 15 kilos between ages 30 and age 60. So menopause is a small slice of the midlife weight gain, and the rest is aging, activity quietly dropping off, and eating that drifts upward so slowly that nobody clocks it. What menopause clearly does is move fat to the midsection, into the deeper, more dangerous visceral compartment around your organs. And that matters for your heart and your health, but it changes where the fat sits more than how much of it there is.

14:03Same equation, just a nudge on the inputs and the change of address. So, four hormones and one pattern. Every one of them is a real modifier, on the burn side or on the appetite side. Real, sometimes worth treating, and every one of them smaller than the story being told. This podcast is brought to you by Factor.

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18:47Jordan Feigenbaum:There's no subscription, you buy it, you own it, it's got a two-year warranty, it's designed and assembled in the USA just north of Charlotte, and a cooler bed is one of the better supported ways to fall asleep faster and honestly I just stopped waking up annoyed and a little sweaty. Visit www.sleep.me slash BBM to get up to$255 off your ChiliPad 2.0 with code BBM. Again, that's www.sleep.me slash BBM. This is available for Barbell Medicine podcast listeners for a limited time. Order today and get free shipping and a 30-day sleep trial. Something we hear a lot from people who run our programs is that they finish one and then they immediately want to start the next one, or that their goals or preferences shifted partway and they want to switch to something different, which is actually how training should work.

19:37Jordan Feigenbaum:It should adapt to you as things change. Now the problem is buying programs one at a time every time that happens well that can be hard on the wallet. So we built Barbell Medicine Premium. One subscription and you get the entire program library in our app. All the strength, hypertrophy, conditioning, rehab, general fitness, beginner programs, and everything in between. You can switch whenever you want and as new programs get added you get them in the subscription. No per program fees ever. Austin and I build and maintain every program and podcast in both libraries. Same people, the same standards as everything else we put out now all in one place.

20:13Jordan Feigenbaum:It's$19.95 a month,$199 for the year. You can cancel anytime. And if you already subscribe to Barbell Medicine Plus or the programming library separately, you can upgrade and we'll sort it out so that you're not paying twice. Link is in the description below. Check it out now. Okay, the third big claim. It's the smartest sounding one on the list, so we're going to spend the most time talking about it. The type of calorie matters, therefore counting the amount is pointless. Now there's a genuine point in here, it's just not the one that most people think that they're making. Remember the category error from the top of the episode?

20:44A calorie is a unit, so a calorie is not really calorie, read literally is nonsense, kind of like an inch is not an inch. But the careful version of it means something real, that two foods with the same calorie count can do different things inside of you. And that's true. It's an argument about what moves the inputs. So let's take it seriously, both halves of it, the burn side and the absorption side. Let's start with the burn side because that's where people overreach. It is true, for example, that protein costs more to digest than carbohydrates or fat. Your body spends something like 20 to 30 % for every calorie from protein just processing it against a few percent for fat.

21:22So the claim goes, eat more protein, raise your metabolism. And technically, yes, that happens. But when you measure it, the effect is very small. If you put people in a metabolic chamber where you can measure every calorie that they burn and swing their protein intake up two or three times how much they were previously eating, their total daily burn barely moves at borderline 50 to 80 calories because their movement quietly drifts down to compensate. Protein's real value is not that thermic rounding error, the thermic effect of food. and we're going to do an entire episode on protein. So I'll give you the short version here and save the rest for that one.

21:57Protein earns its keep when it comes to reducing your dietary intake. It does tend to keep you fuller to some extent, but more importantly, it crowds the higher calorie food off of your plate. Now, whether the benefit is mostly from the fullness, like most people say, or really displacing the food, which less people say, my read of the literature is mostly from displacing the other higher calorie food. But we're going to cover this in detail on the protein episode. Now here's the best test, in my opinion, of whether the type of calorie is what decides how much fat you're carrying. Researchers overfed people by about 950 calories a day for two months, and they varied the protein from 5 % of the diet all the way up to 25%.