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

The host opens with part two of Dr. Jason Fung's book, titled "the calorie deception." That section lists five wrong assumptions about obesity and weight loss. One is that calories in and calories out are independent of each other. Another is that basal metabolic rate stays stable. The host connects this to a common cultural explanation for obesity, having a "low metabolism," and asks whether it has any merit. Fung answers, "Oh, absolutely."

Fung starts from the energy balance equation: body fat equals calories in minus calories out. He says this equation leads people to advise eating 500 fewer calories a day to lose a pound of fat per week. He calls that advice "unquestionably false" and grounds his objection in metabolic adaptation, the idea that the body lowers its energy use when intake drops.

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.

He defines basal metabolic rate as the number of calories the body spends in one day. He says this effect appears in "almost every single study" and has been known "for like 80 years at least." In the same answer he speaks of studies "over the last 50 years." His conclusion is that cutting calories also cuts calories burned, which limits weight loss. In the extreme case he describes, a person eats 500 less, burns 500 less, and loses no body weight. He does not name any specific studies in this stretch of the interview.

The host asks what happens after a diet ends and whether metabolism stays low. Fung links this to yo-yo dieting and walks through a worked example. The starting point is 2,000 calories in and 2,000 out, with weight stable. The dieter drops to 1,500 calories and expects body fat to make up the remaining 500.

In Fung's account, the outcome depends on what and how often the person eats. He describes eating "10 times a day, 8 times a day like people say you should," eating low fat or "tons of carbs," and so "spiking your insulin." His central physiological claim is that "Insulin prevents you from burning body fat," and again he says this has been known for 80 years. When insulin stays high, he argues, the body still wants 2,000 calories but can't draw on stored fat.

It's like it's in the bank and the bank is closed. You can't take it out.

Since the equation has to balance, Fung says the body can only burn the 1,500 calories coming in. Metabolic rate falls by 500 calories and no body fat is lost. He lists the felt effects: tiredness from burning fewer calories, feeling cold from not having enough energy to make body heat, and hunger.