Résumé de Burn

In Burn, Herman Pontzer draws on his fieldwork with the Hadza, a hunter-gatherer community in northern Tanzania, to challenge the common assumption that strenuous daily activity burns far more calories than a sedentary Western life. Pontzer, an evolutionary anthropologist and Duke University professor, spent years measuring energy expenditure using doubly labeled water, and his results form the book's central puzzle: the Hadza walk miles each day yet burn roughly the same total calories as adults in the United States and Europe. He calls this the constrained total energy expenditure model, arguing that the body maintains a relatively fixed daily calorie budget and reallocates energy among tasks like physical activity, immune defense, and reproduction rather than simply adding more. The book uses that finding to reframe metabolism, weight gain, and exercise. Pontzer shows that metabolism isn't a furnace that revs up or stalls according to how much you move; humans evolved to manage a limited energy budget, which helps explain why hard workouts often don't produce proportional weight loss and why diet, not activity alone, drives much of the obesity epidemic. He traces human energy use across the life span, from infancy through old age, and contrasts our biology with that of other primates and mammals to show how unique our energy strategy is. Burn also functions as a memoir of scientific fieldwork, describing the sweat, improvisation, and cultural exchange involved in studying Hadza volunteers. Pontzer concludes that exercise remains vital for health—especially heart, brain, and metabolic function—even if it doesn't torch as many extra calories as advertised, and that understanding our evolved energy budget can lead to more realistic expectations about diet and activity.