E-News Exclusive

New Perspective on the Role of Exercise in Weight Loss

By Densie Webb, PhD, RD

“Eat right and exercise” is the long-held advice for helping clients and patients lose weight. But is it the best recommendation? The dietary aspect of this advice still stands strong—eat more fruits, vegetables, and whole grains, and less sugar, salt, saturated fat, and avoid overly processed foods. None of this has changed. However, one researcher is challenging the second half of this recommendation, ie, that exercising more will help your clients and patients lose weight.

Herman Pontzer, PhD, a professor of evolutionary anthropology and global health at Duke University in Durham, North Carolina, and author of Burn, says people should reframe how they think about exercise, and health care practitioners should rethink their advice to individuals trying to lose weight. His point of view, which he explains in Burn, is that the way in which the body burns energy is poorly understood, and individuals have gotten the science of energy expenditure fundamentally wrong. It’s not just a matter of what’s typically viewed as calories in and calories out, he says. The body isn’t a product of engineering like a fuel-burning machine, it’s a product of evolution and the human body has evolved to adapt to food intake and conserve energy for survival.

While some of what Pontzer says may seem surprising, many surmise it makes sense. Pontzer says: “People who are physically active each day often have the same daily energy expenditure as people who are more sedentary, even if we’re comparing people who are the same size and percent body fat. People who start a new exercise program will increase their daily energy expenditure initially. But, after a few months, the body seems to adjust and daily energy expenditure will be close to, or even the same as it was before they started exercising.”

Pontzer has studied how many calories the approximately 37.2 trillion cells in the body burn in a 24-hour period by studying the Hazda, a hunter-gatherer people in Tanzania, which he discusses in detail in his book. To his surprise, he found that even though the Hazda spend their days literally hunting and gathering, they tended to burn the same number of calories as a person of similar size and age in the United States and in Europe. He believes that instead of burning more calories from activity, the Hazda have adapted and adjusted to the high level of physical activity. He says it’s a way of making the energy books balance, a rejuggling of the energy budget.

He also has been involved in research that looked at healthy individuals from more than 20 countries and found that total energy expenditure isn’t protective against weight or body fat gain.1 The bottom line is that the body doesn’t seem to want to change the energy it expends very much. The researchers of that study concluded that more evidence is needed about the cause and consequences of differences in total energy expenditure among individuals and why those differences appear to be mostly unrelated to weight gain or weight loss.

Even among athletes, there’s a leveling off of energy expenditure.2 Pontzer also was involved in a study that included runners, triathletes, and participants in long-distance cycling races and found that no matter the event, energy expenditures leveled off after about 20 days.

While it may seem counterintuitive to everything Pontzer has said, he does acknowledge that after about the age of 60, energy expenditure drops by about 7% per year. Some of this is due to a loss of muscle mass that occurs with age, partly due to reduced physical activity and the fact that cells in the body become less metabolically active as individuals get older.

He doesn’t deny the fact that exercise is critically important for health. Exercise can improve mood and mental sharpness, and it can help reduce the risk of several chronic diseases. “We should focus on those benefits, which are well supported by tons of evidence, rather than promising weight loss,” he says. “When we sell exercise as a weight loss tool, we’re asking for unhappy clients.” His advice? “Diet is the best tool for weight loss and weight management in general. Exercise is essential for other aspects of health, so you really need both.”

— Densie Webb, PhD, RD, is a freelance writer and editor and industry consultant based in Austin, Texas.


1. Thurber C, Dugas LR, Ocobock C, Carlson B, Speakman JR, Pontzer H. Extreme events reveal an alimentary limit on sustained maximal human energy expenditure. Sci Adv. 2019;5(6):eaaw0341.

2. Rimbach R, Yamada Y, Sagayama H, et al. Total energy expenditure is repeatable in adults but not associated with short-term changes in body composition. Nat Commun. 2022;13(1):99.