The Diary Of A CEO with Steven Bartlett
Most Replayed Moment: Calories In, Calories Out Is A Myth! Why Most Diets Fail - Dr. Jason Fung
31 Oct 2025
Chapter 1: What is the calorie deception and why is it important?
in part two of your book you say the calorie deception yeah and you say there are five wrong assumptions about obesity and weight loss the calorie calorie calorie in calorie out are independent of each other so won't trigger one another and this interesting point about the basal metabolic rate being stable yeah is that in essence because people you know people will often say i have a low metabolism it's kind of like a word in culture if someone is um obese often they're
the diagnosis is they have a low metabolism. Is there any merit in that? Is that true?
Oh, absolutely. The question, so when you think about, so body fat, you think about the energy balance equation, body fat equals calories in minus calories out. This often leads people to say, well, just eat 500 fewer calories and you'll lose a pound of fat per week.
It's unquestionably false because every single study that we've done over the last 50 years shows that if you eat 500 fewer calories, then over time, depending on what foods you're eating, eventually your body will just burn 500 fewer calories. So that's your basal metabolic rate, the number of calories that your body is expending in one day. So we see this in almost every single study.
We've known about it for like 80 years at least. You eat fewer calories, your body burns fewer calories. Well, that's going to limit how much weight you're gonna lose, right? So this idea that just eat fewer calories will automatically lead to weight loss is completely false because we know that eating fewer calories leads also to burning fewer calories
So you eat 500 less, your body burns 500 less, and you're not losing any body weight.
So I go on a diet, let's say, because I'm trying to lose weight. My metabolism lowers to meet the calorific restriction that I've imposed on myself. What then happens when I come off the diet? Does my metabolism stay the same? Generally, yes. Low?
Yeah. So that's that yo-yo dieting effect. So say you start with 2,000 calories in, 2,000 calories out. You're not gaining weight. You're not losing weight, right? Now you decide, okay, I'm going to go on a diet. So you go down to 1,500 calories thinking that you're going to burn 2,000. and the body fat's gonna provide 500, right? That's how you balance that equation.
However, if you eat the wrong foods and you're eating all the time, so you're eating 10 times a day, eight times a day, like people say you should, you're eating low fats or you're eating tons of carbs, you're spiking your insulin. Insulin prevents you from burning body fat, okay? So again, we've known about this for 80 years.
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Chapter 2: How does basal metabolic rate affect weight loss?
You're taking in 1500, Your body is now burning 2000, but you can't burn any body fat. So the calories that are stored in your body fat cannot be sort of taken out. It's like it's in the bank and the bank is closed. You can't take it out. So what's gonna happen? Well, you don't have a balanced equation. So that cannot happen.
So what happens is that in order to balance that equation, because your insulin levels are high, you're eating 1500 calories coming in, your body can only burn 1500 calories. Your metabolic rate has just now gone down by 500 calories. And guess what? You're not losing any body fat. So that's an example of how the calories idea is completely wrong.
Because if you continue to do that, what's going to happen over time is that you get tired because you're burning fewer calories. You don't have enough energy to generate body heat. So you're cold, you're tired, you're hungry. So you say, okay, I'm going to go to 1800 calories. So now you're eating 1800 calories, but you're only burning 1500 calories. Guess what? You gain weight.
And you say, but how can I gain weight? I'm eating less than I did. Yes, you are eating less than the 2000 calories you used to eat. You're eating 1800, but you're eating the wrong foods. It's very high insulin foods. So therefore you're going to gain weight. In fact, everybody says that. And all the nutritionists, all the doctors, they just don't believe them.
They say, you're lying, you're cheating. You're eating more than you think.
So this explains something that happened with one of my friends, which always puzzled me. He swears by the calories in calorie out thing. I've spoken about him a few times. He posts about it online as well. And he actually managed to get a pretty much like six pack abs, pretty much. And at the time, it appears that he was eating a lot of Domino's pizzas, a lot of pizzas.
And I was thinking, how's this guy eating all these pizzas, but he's using his calories in calorie out thing. And then when the pizza stopped...
Yeah.
There was this yo-yo effect. Yeah. Where he managed to get to basically what I'd describe as a six pack or thereabouts. And then stopped the diet per se. And then there was this big yo-yo effect, which I imagine is what you've said there. What he's done is he's lowered his metabolism. And when he goes up just a little bit. It all comes back. It all comes back. And then some. And then some.
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Chapter 3: Why do traditional diets often fail?
Oh, it's very detrimental. And that's what yo-yo dieting, we all know it's very detrimental. But think about it differently, right? So let's take a different example with the same calories, which is why I keep saying you have to think about more than the calories. You have to think about what the hormones are because that's the instructions to your body.
food contains calories energy but it contains instructions as to what to do so let's take an example you're eating 2000 calories in 2000 calories out now you go on a diet you want to you take in 1500 but what you do is you do some intermittent fasting when you fast insulin is going to fall that's the whole point insulin is a hormone that goes up when you eat it goes down when you don't eat right so
When you eat, insulin goes up. Your body wants to store energy. When you don't eat, insulin goes down. Your body says, I have no energy. I have no food coming in. Please take it out of storage. So now you take 1500 calories, but you do intermittent fasting. So you're allowing your insulin levels to fall. Now, 1500 calories are coming in. Insulin levels are low.
Your body wants to burn 2000 calories. It says, well, insulin levels are low. Let me take 500 calories from my body fat. Guess what? You have 500 coming from your body fat. You have 1,500 coming from your foods. You burn 2,000. It's a balanced equation. So instead of the opposite situation, and you see that the calories are the same. You went from 2,000 in to 1,500 in.
But what the difference was that you allowed insulin to fall, which allowed you to burn body fat, right? It's the hormonal signal that says... Please take energy out, open up the doors so that body fat can come out. And this is the piece that's missing because people are all like, well, I'm this, I'm that. And it's like, well, why can't you burn the fat that's on your body?
Because there's 200, 300,000 calories of body fat. Why can't you access it? It's because you haven't activated the right hormones so that you can access it. So now if you do intermittent fasting, you eat 1500 calories, you take 500 calories out, your body's burning 2000. Now all of a sudden, if you go off your diet and you go back to 2000 calories, guess what?
You don't gain weight, you don't lose weight. Same as before. Whereas before you go even to 1800 calories, you lost weight. But the difference was not the calories, it was always 2000 to 500. The difference was you paid attention to the hormones that you're telling your body. And the insulin is sort of the primary hormone. There's actually a lot more. There's cortisol is a very important hormone.
There's other hormones. You mentioned burning calories there. One of the thoughts around the calories in calories out model is that you can just exercise. And if you burn a thousand calories exercising, then that gives you a little bit of a reserve there to eat more, for example. Yeah.
Yeah, and it's probably a very, very small effect for a couple of reasons. So we know that if you exercise, and I say this, exercise is really good for you in a number of ways. Flexibility, strength, core, all kinds of things. So very, very important. But in terms of weight loss, it's actually a very, very small effect. Why?
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Chapter 4: What role does insulin play in weight management?
But most people I deal with, which are sort of middle-aged and higher, you're talking about sort of a quick walk or, you know, 45, half an hour, three times a week sort of thing. And if you ever go on the treadmill and you ever watch the calorie counter on the treadmill, you know it goes up very, very slowly, right?
You'll do half an hour and it'll be up to like 120 calories or something like that, right? So that exercise really didn't burn off very many calories. It's the amount that you'd get in a couple of cookies, for example, right? So it's just... numerically it's just very small.
So if your body is normally using 2000 calories with your brain generating body heat, your heart, your lungs, your liver, they're using 2000 calories and now you go up to 2100 calories. Well, percentage wise, it's not a huge deal, right? The other problem with exercise is that it tends to actually cause you to eat more. So again, we've had decades of study for this.
If you exercise, during the exercise, you have reduced appetite. So you have, it's called exercise-induced anorexia. So in the middle of a basketball game, you don't suddenly go, oh, wow, I'm really hungry, right? Because your blood is flowing in your muscles and so on. You're not thinking about the hunger. So hunger actually goes down during exercise. But after exercise, we see this rebound.
So we see that people are actually more hungry after exercise. And if you're hungrier after exercise, it's gonna cause you to tend to gain more weight. In fact, there's this very interesting study that was done a few years ago in Harvard where they measured the sort of calorie difference that you get for children in certain activities. So they said, okay, what if a child is watching TV?
What's the average caloric difference? And it was like plus 100 calories per hour. So for every hour of TV, they're sort of positive 100 calories over time, right? And that makes sense. You're just sitting there. When you look at mild exercise, it's about the same. It's about positive 100 calories. So the only way that happens is that if that exercise is causing you to eat more, right?
And you say, well, why are you eating more? It's like, well, because you're hungry. Like the exercise is inducing you to eat more and that's gonna make it difficult to lose weight, right?
You say in the book in chapter four that 95% of weight loss is diet. Yeah.
And that's the reason why exercise is very hard to exercise enough to lose weight. And that's not to say that you shouldn't exercise. You really should exercise. Everybody should exercise. But if you're trying to lose weight, you still got to focus on the main thing. topic, which is the foods that you eat, which is not just the calories.
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Chapter 5: How does intermittent fasting change the weight loss equation?
That's after dinner until the next day's meal, which is breakfast, right? So say you stop eating at 6 p.m., you eat at 8 a.m. That's a 14-hour period where your body... is not eating, it's fasting, and therefore it's gonna use calories, right? But the word breakfast tells us that that's actually a normal pattern, this normal cyclical pattern. You feed, then you fast, right?
If you eat all the time, your body's just gonna store energy and never have a period to burn energy. So, okay, well, what's gonna happen? You're gonna gain weight.
What you just listened to was a most replayed moment from a previous episode. If you want to listen to that full episode, I've linked it down below. Check the description. Thank you.