A new study involving over 4,000 people across 34 countries suggests that physical inactivity may not be the primary driver of the obesity epidemic. Researchers, including Herman Pontzer, compared calorie expenditure among individuals with varying activity levels and found surprisingly little difference after adjusting for body size. This challenges the long-held belief that insufficient exercise is the main culprit behind rising obesity rates.

The study, published in the scientific journal PNAS, supports the theory of “constrained total energy expenditure,” a concept proposed by Pontzer over a decade ago. According to this theory, the body compensates for increased physical activity by reducing energy expenditure in other areas. For example, if you burn 700 calories during a run, your body might reduce combustion in the immune system or decrease your sex drive to compensate, ultimately resulting in a smaller net calorie deficit.

Jens Lund, a body weight researcher at the University of Copenhagen, who helped evaluate the study, emphasizes that the findings should not discourage exercise. While exercise may not be as effective for weight loss as previously thought, it remains crucial for overall health.

The study suggests that focusing on eating habits is essential to combat the obesity epidemic. Herman Pontzer argues that increased energy intake has played a significantly larger role than decreased energy expenditure in the rise of obesity.

Researchers are still trying to understand why the body defends fat stores so strongly, even in individuals who are already overweight. One theory is that weight gain itself can lead to a higher calorie intake, as the body requires more energy to maintain larger fat stores.

The findings of this study could help reduce the stigma associated with being overweight or obese. People who struggle with their weight are often told to exercise more, but this study suggests that other factors may be more important contributors to their condition.