Most Replayed Moment: Calories In, Calories Out Is A Myth! Why Most Diets Fail - Dr. Jason Fung

Steven Bartlett (0:04)

In part two of your book, you say the calorie deception. And you say there are five wrong assumptions about obesity and weight loss. The 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, is that in essence, because people will often say, I have a low metabolism. It's kind of like a word in culture. If someone is obese, often the diagnosis is they have a low metabolism. Is there any merit in that?

Jason Fung (0:34)

Oh, absolutely. The question, so when you think about 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 going to lose, right? So this idea that just eat fewer calories will automatically lead to weight loss is completely 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.

Steven Bartlett (1:47)

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 low?

Jason Fung (2:04)

Yeah. So that's that yo-yo dieting effect. So say you start with 2000 calories in, 2000 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 1500 calories, thinking that you're going to burn 2000 and the body fat is going to 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, 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. So now, you eat 1500 calories, but you're keeping your insulin levels really high. So fewer calories, but lots of high carb foods, eating all the time, insulin stays high. 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 going to 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 whole, 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.

Steven Bartlett (4:25)

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.