Calorie Deficit, Diet and Exercise – The Science

In this 2022 landmark review paper, Kevin Hall leads an international team of renowned obesity scientists to describe the Energy Balance Model (EBM) of Obesity as the prevailing model as to how and why weight gain and weight loss happen. The paper at the same time describes how the carbohydrate insulin hypotheses, the theoretical foundation of low carb dieting, ketogenic dieting and intermittent fasting is convincingly invalidated.  


Here is a key metabolic ward cross-over study validating the EBM. In this study ad lib calorie intake was almost 700 cal/day more in a plant based low fat diet – compared to an animal based ketogenic low-carbohydrate diet.


The DIETFITS Randomized Clinical Trial. DIETFITS may be the most rigorous diet comparison study ever done. The study was conducted by the talented Stanford researcher Christopher Gardner. The study compared a whole food low-fat diet to a whole food low-carbohydrate diet in 609 subjects over a period of 12 months. Each subject attended 22 sessions with a registered dietitian; no calorie intake targets were given. The study looked to see if genotypes or insulin production predict weight loss. DEXA was used again to measure body composition, and metabolism was also measured. The study showed no significant differences in weight loss between the two groups. Also, it was found that neither genetics nor insulin levels could predict weight loss. Again, differences in adherence were more important than differences in diet.

Surprisingly, studies show that exercise alone will not promote significant weight loss in most people. 


In an important systematic review and meta-analysis of randomized controlled trials, researchers found that moderate intensity exercise programmes of 6 to 12 months’ duration were associated with only modest improvements in weight (~4 pounds), waist circumference (~2cm) and cardiovascular risk in overweight and obese populations.


In a landmark clinical trial, Herman Pontzer and colleagues show that though low levels of physical activity increase the number of calories we burn, for higher levels of activity there is no expected rise in energy expenditure and that the body adapts to maintain total energy expenditure within a narrow range. This is called the constrained model of energy expenditure.


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