Exercise is not key to losing weight: what science reveals about human metabolism
Does exercise really help with weight loss?
Although the idea that moving more equals losing weight remains popular, recent research suggests that exercise alone rarely works as a primary tool for shedding pounds. According to anthropologist Herman Pontzer, author of the book Burn, the relationship between physical activity and weight loss is more complex than we think. This discovery, based on the restricted energy expenditure model, could transform our understanding of strategies for weight control.
Why doesn't exercise burn as many calories as we think?
For decades, the notion that engaging in more physical activity is the key to burning calories and, consequently, losing weight has been promoted. However, research led by Herman Pontzer and his team has called this belief into question. Studying the Hadza, a tribe of hunter-gatherers in Tanzania, they found that despite their extremely active lifestyle, members of this community did not burn significantly more calories than an average person with a sedentary lifestyle in a developed country.
The finding was puzzling. The Hadza walk kilometers daily, carry heavy objects, and perform physically demanding tasks. Their caloric expenditure was expected to be very high, but the data revealed that their metabolism operated within a limited energy range. This led to the development of the restricted energy expenditure model, which proposes that our body regulates energy consumption to keep it stable in the long term, regardless of activity level.
The restricted energy expenditure model: the key behind the myth
According to this model, when we regularly increase our physical activity, the body adjusts other metabolic functions to save energy. For example, it may reduce expenditure on processes such as digestion or body temperature regulation. This explains why many people who exercise consistently do not experience significant weight loss. The body compensates for increases in activity by limiting calorie burning in other areas.
“If you exercise today, you burn more calories today,” Pontzer explains, “but if you change your lifestyle to incorporate physical activity regularly, your body adjusts and you end up not burning more calories overall.” This evolutionary mechanism likely arose to ensure survival, allowing humans to adapt to periods of high physical demand without depleting all their energy.
Nutrition and aging: the true culprits of weight gain
If exercise is not the determining factor in weight loss, why do so many people continue to struggle with gaining pounds? Pontzer points out that the problem lies not in metabolism, but in the calories consumed. As we age, we tend to eat more, and our bodies become more efficient at storing energy as fat. This, combined with unhealthy eating habits, contributes to weight gain.
During the holidays, when overeating is common, it is easy to exceed daily caloric expenditure, even for those who maintain an active routine. This pattern, accumulated year after year, leads to the weight gain that many experience over time.
Exercise and overall health: an ally, but not a magic solution
Although exercise may not be the key to losing weight, it remains essential for overall health. It helps prevent chronic diseases such as diabetes, hypertension, and cardiovascular problems. However, focusing solely on exercise as a solution for weight loss can be counterproductive. Instead, adopting a balanced diet and sustainable long-term habits is much more effective.
It is common to see advertisements and products that promise to speed up metabolism, but science has shown that these supplements or miracle diets have minimal, if any, impact on total caloric expenditure. “You can follow a low-carb or high-protein diet, but that won't have a measurable effect on the number of calories burned,” Pontzer states.
Changing the focus: balance between nutrition and physical activity
The central message of this research is not to abandon exercise, but to understand its true role in weight control. While it cannot guarantee weight loss on its own, it is essential for a healthy life. The key lies in finding a balance between calories consumed and burned, along with sustainable strategies that improve eating habits.
Moreover, by accepting that the human body has limits on the number of calories it can expend, we can avoid frustrations and adjust our expectations. True change requires addressing both physical activity and the quality and quantity of the foods we consume.