This conversation is with Herman Pontzer, an evolutionary anthropologist and professor at Duke University. Herman is best known for his groundbreaking work on human metabolism and energetics, which challenges long-held assumptions about how our bodies burn and manage energy. His field research with hunter-gatherer and subsistence-farming populations—including the Hadza of Tanzania, the Daasanach of Kenya, and the Tsimane’ of Bolivia—has redefined what we know about the relationship between activity, diet, and health.

We begin by exploring the deceptively simple question: Why do some people burn more calories than others? Herman explains how the body’s total energy expenditure is remarkably constrained, meaning that even when we exercise more, our bodies often compensate by reducing energy spent elsewhere. This insight challenges the familiar “calories in, calories out” model and reframes how we understand diet, obesity, and modern sedentary lifestyles. Together, we discuss how evolution has shaped the human metabolic system—from the daily life of foragers walking 19,000 steps a day to the physiology of those in industrialized societies.

We examine how metabolism interacts with the immune system, reproduction, and brain function, and why understanding these trade-offs is key to improving public health. Herman also shares insights from his books Burn and Adaptable, connecting metabolic research to broader questions about longevity, diet quality, and the future of medicine. Finally, we consider how modern tools—from doubly labeled water to GLP-1 drugs—fit into the long story of how humans manage energy in a changing world.