Losing weight is hard. That’s probably why almost three-fourths of American adults are overweight or obese. On this episode, we speak with a distinguished doctor and former FDA commissioner who has personal experience struggling with the scale. In this discussion of popular weight-loss drugs like Wegovy, we tackle the biology of weight. We also interview an evolutionary anthropologist about some human populations that don’t have problems with obesity. Is their active hunter-gatherer lifestyle burning more calories?
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Has the Food Industry Hijacked the Biology of Weight?
While Dr. David Kessler (our first guest on this episode) was FDA Commissioner, from 1990 to 1996, the agency made some major strides towards helping people understand what they are eating. That is when Nutrition Facts labels were standardized and required on all packaged food. In the US, if you buy food that is in a package, that Nutrition Facts label will tell you how big the serving is, how many calories per serving, and also data like the amounts of protein, carbohydrates, fat, and certain vitamins and minerals are supplied by each serving. If information were all that we needed to choose exactly what and how much to eat, there would be no weight problems. Yet Dr. Kessler’s own difficulties with the 10 pm cravings will not sound strange to many of us. The biology of weight may appear straightforward, but the allure of fat, salt and sugar to our reward centers may bypass rational decision-making.
One of Dr. Kessler’s great achievements as FDA Commissioner was holding the tobacco industry to account. How has the food industry escaped similar scrutiny? It seems that the ultraprocessed foods that seem convenient and affordable are contributing to the toxic fat making us sick.
GLP-1 Drugs to the Rescue:
Given the difficulties people have trying to lose weight, it is no surprise that the GLP-1 receptor agonists like semaglutide (Wegovy and Ozempic) or tirzepatide (Zepbound and Mounjaro) have become popular. They seem to reduce the urge to eat and calm the food noise in people’s heads. Those 10 pm cravings Dr. Kessler describes disappear under the influence of these weight loss drug. He has taken such a medication himself to drop the 40 pounds he gained during the intense work period of the COVID-19 pandemic. These medications will be very helpful for many people, but they do have some serious side effects. (You can learn more here.) Healthcare should utilize them as a powerful tool, but just one in a toolbox that should have several.
How Does Exercise Affect the Biology of Weight?
The famous mantra, calories in calories out, suggests that we might be able to exercise our way to a healthy weight. After all, if you burn more calories than you take in, you should lose weight. But anthropologist Herman Pontzer, PhD, has studied people’s energy expenditures around the world. He and his colleagues used a sophisticated technique called double-labeled water to track the energy people burn.
According to their data, humans’ daily energy needs don’t vary as much as we’d think, even when physical activity is vastly different. The Hadza, who get their dinner by tracking, hunting with bow and arrow and running after the injured animal, somehow use roughly the same amount of energy as Americans shopping at the grocery store. Their physical activity is enormously higher, though. (Check out this publication at the Proceedings of the National Academy of Sciences.) Apparently, we need to pay more attention to the calories (actually kilocalories) we consume if we want to understand the biology of weight.
This Week’s Guests:
David A. Kessler, MD, served as chief science officer of the White House COVID-19 Response Team under President Joe Biden and previously served as commissioner of the US Food and Drug Administration under Presidents George H.W. Bush and Bill Clinton. Dr. Kessler is a pediatrician and has been the dean of the medical schools at Yale and the University of California, San Francisco. He is the author of the New York Times bestsellers The End of Overeating and Capture and two other books: Fast Carbs, Slow Carbs and A Question of Intent. Dr. Kessler’s latest book is DIET, DRUGS, AND DOPAMINE: The New Science of Achieving a Healthy Weight.
David A. Kessler, MD. Photo copyright Joy Asico Smith
Herman Pontzer, PhD, is Professor of Evolutionary Anthropology and Global Health at the Duke Global Health Institute. Dr. Pontzer is the author of Burn: New Research Blows the Lid Off How We Really Burn Calories, Stay Healthy, and Lose Weight. His latest book is Adaptable: How Your Unique Body Really Works and Why Our Biology Unites Us.
Herman Pontzer, PhD, Duke Global Health Institute
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Listen to the Podcast:
The podcast of this program will be available Monday, Oct. 20, 2025, after broadcast on Oct. 18. You can stream the show from this site and download the podcast for free.
Citations
- McGrosky A et al, "Energy expenditure and obesity across the economic spectrum." PNAS, July 14, 2025. https://doi.org/10.1073/pnas.2420902122
