Well past 20,000 steps, my sister and I reached the top of Stonewall Peak at 5,730 feet. Failing to lose weight running marathons, she climbed three Colorado 14ers—more than 42,000 feet in elevation. Not being one to give up easily, she swam two miles of open water for the Alcatraz Swim.
The net result? No loss of weight.
All our activity was misguided. What’s worse, we received bad information from our most trusted authorities, including the World Health Organization, the NIH, the CDC, the Mayo Clinic, and even Michelle Obama. They tell us a falsehood: for successful weight loss, eat less and exercise more. The truth is that exercise is imperative for our health but it won’t help us lose weight.
Decade of Research
We look at both sides, butt heads with the best, and accept not conventional wisdom but the newest findings as correct. Two things to remember:
- Herman Pontzer is the most visible spokesperson for the new research that detached physical activity from weight loss.
- Advances in the doubly labeled water technique allowed the first accurate measurements of total energy expenditure, or TEE, in humans about 40 years ago. In doubly labeled water, the hydrogen and oxygen are replaced with isotopes that can be tracked.
Pontzer and colleagues traveled to study the Hadza tribe of hunter-gatherers in Tanzania. With data for 30 adults and controlling for body size, they unexpectedly found in 2012 that Hadzas walk several miles every day but eat no more than we do. Very roughly, their diet is meat, tubers, berries, parts of the Baobab tree, and perhaps 10% honey.
Hadza TEE is about equal to the average daily effort in the U.S. and Europe, where people are far less physically active. The researchers hypothesized that TEE is a relatively stable, constrained physiological trait. And that universally, after considering gender, body size differences, and regardless of their physical activity, people all need to consume the same amount of energy.
Over the past decade, this study has been viewed a quarter million times. In 2015 Pontzer first proposed constrained TEE. Further work in 2016 on 322 individuals in five countries resulted in ten authors making a formal group presentation of the Constrained Total Energy Expenditure model.
We have two models. In the old, traditional, additive model (Figure 1, top), TEE increases in a linear dose-response relationship with physical activity.
Instead, Pontzer believes, TEE evolved as a metabolic strategy that is true for everybody: those with sedentary and active lifestyles alike.
In the new, proposed, constrained model (Figure 1, bottom), TEE increases slightly only in the very lowest range of physical activity. Then if physical activity increases, TEE is held to a flatline. Constraint forces a decrease in available energy for the non-physical activities that traditionally were said to take roughly 70% to 80% of our total energy (including the energy our body needs to function at rest; the immune system; fighting inflammation; growth in youth; reproduction in adults; plus 10% to digest our food).
In constrained TEE, the enormous non-physical-activity component is not a constant. It dynamically changes so total energy expenditure is bound within a very narrow range that is effectively a set point.
To bring his work to a popular audience, Pontzer published once in The New York Times, twice in Scientific American, and agreed to interviews. To consolidate his view, he published the book Burn in 2021.
I worried about his methods until an interviewee reassured me that Pontzer’s data is exemplary. Lest you wonder, too, Pontzer is part of an all-star cast of 87 researchers who standardized the doubly labeled water measurement of TEE in 2021.
Increasingly, Pontzer is not alone. Scientists and related studies have shown that weight loss and exercise are without correlation. Otherwise, the Hadza would be skin and bones.
A Bit of History
In the 1950s, Jean Mayer, the renowned tenth president of Tufts, concluded erroneously that inactivity, not overeating, is a cause of childhood obesity. Mayer’s view held as truth until the 1980s.
I fear Tufts’s Christina Economos mistakenly unleashed on children a firehose of interventions including more physical activity in Shape Up Somerville. Dr. Economos did not respond to three emailed requests for comment.
We didn’t know any better twenty years ago, when Marion Nestle and her colleague asked for changes in public health policy to stop the obesity epidemic. When I asked her if the weight loss guideline to “eat less, exercise more” could be shortened to “eat less,” Nestle took exception.
“It’s always good to link weight loss to overall health. Weight is a risk factor, not a death sentence for most people.” Nestle says, “For weight loss, eating less is essential. For overall health, being active is essential.”
Nestle insists on linking two independent facts—baffling, coming from the author of Food Politics. Her book was in large part about the insatiable food industry that can’t be satisfied with anything other than eat more. Disappointing, because overall, my takeaway was a whispered eat less.
Scan of the Popular Press
The popular press has given the issue mixed support. Gretchen Reynolds, the phys-ed columnist at The New York Times, has opinions on the subject that flip and flop. She flipped again last year.
The competition, however, didn’t miss the signal. Julia Belluz led in 2016 with Pontzer for Vox, where she wrote that those who promote exercise for weight loss are “leading us astray in our fight against obesity.”
Belluz repeated her message in Vox in 2018, citing a fellow Canadian who is trying to rebrand exercise. Both are adamant, make exhaustive reviews of the literature, and support their views with evidence. Exercise and weight loss are not correlated.
Susan Roberts and Sai Das published in Scientific American in 2017, citing Pontzer’s finding of similar caloric needs among populations with very different amounts of physical activity.
Dueling Opinions
Some people cling to the opposing view. James O. Hill, a famed obesity researcher who leads a Coca-Cola industry group that favors exercise, has talked with Pontzer and agrees with him that at some point exercise does not increase TEE. However, Hill still thinks exercise will decrease body weight. To help resolve the point, I sent him a copy of Pontzer’s book as a gift.
As a group, researchers disagree on the cause of obesity. Certainly, Gary Taubes, a writer who also funds research, wrote 14 years ago that exercise won’t help us lose weight. But he writes with Harvard’s David Ludwig and Walter Willett and others in 2021 that “rigorous research is needed” to “generate new models that best encompass the evidence.”
Researchers politely entertain all sides, as they descend into labeling logical fallacies. They have argued, criticized their opponents, and defended themselves—for a century now. Meanwhile, some of us would like to lose weight.
I asked Roberts and Das if weight loss guidelines could be shortened to “eat less.” Roberts wrote, “Based on our research it would be as effective and probably it would reach more people.”
Roberts went on to advocate a blended approach (ideally, diet plus exercise if you can, or only diet if you can’t) but I resist her embellishment. Pontzer writes, “I think we’d get farther with obesity prevention by putting all our emphasis on diet.”
Sports Medicine
A review in 2013 of the positions taken by the American College of Sports Medicine (ACSM) found response to exercise is personalized. Responses range from weight gain to clinically significant weight loss. Some in the sports medicine field report success. Some suggest shifting the goal away from body weight to different health markers. Some report that exercise’s effect is nonexistent or modest.
ACSM published exercise recommendations in 2009 to cover obesity prevention, obesity treatment, and weight loss maintenance. They reported disappointing evidence for most things, with the rationales that few randomized controlled trials exist, and the trials that do exist are small in size.
Going Forward
Hans Christian Andersen knew a swindle when he saw one. His The Emperor’s New Clothes became a modern idiom for claims we are unwilling to surrender. Sports medicine guidelines are cited widely as fact. The world must live with those assertions, until the day someone calls out the obvious: You can’t outrun a bad diet.
Please don’t misunderstand these words. Exercise is a miracle cure you should make time for every day. Physical activity has staggering health benefits—more than those of any drug. But the necessity of regular physical activity notwithstanding, we have an obesity pandemic on our hands. Approximately 75 percent of American adults are overweight or obese. Our public health guidelines for weight loss are wrong: The bottom line is eat less.
Appendix: Selected Sources
Pontzer, Herman, David A. Raichlen, Brian M. Wood, Audax Z. P. Mabulla, Susan B. Racette, and Frank W. Marlowe. “Hunter-Gatherer Energetics and Human Obesity.” PLOS ONE 7, no. 7 (July 25, 2012): e40503. https://doi.org/10.1371/journal.pone.0040503.
Pontzer, Herman. “Burn: New Research Blows the Lid off How We Really Burn Calories, Lose Weight, and
Stay Healthy.” ISBN: 9780525541523. Avery, an Imprint of Penguin Random House, 2021.
Special Thanks to Amy Luke
Amy Luke, PhD: E2HD Seminar Series – March 23, 2018. https://www.youtube.com/watch?v=7dPrkX7m32w.
Susan Lesch recently received an MNSP from the Friedman School. She hopes
America will rewrite its weight loss guidelines so they work. She prays that
Friedman will restore obesity to the MNSP curriculum. Susan follows
professional women’s basketball, and this year she’ll root for Alyssa Thomas
and the Connecticut Sun. You can reach her at Susan.Lesch@tufts.edu.
The Friedman Sprout 
Hoping to drop about 15 pounds, I am now eight weeks into my own new fitness regimen. As of today, I have a slimmer body, more muscle, a lower resting heart rate, and . . . higher numbers on the scale. If weight is all that matters, surely exercise is not the answer. While men tend to aim for weight gain in the gym, women seem to think the same efforts will result in weight loss, but why would that be? What I think many of us are actually seeking through exercise is fitness, personal satisfaction, and (dare I say) sexual appeal. For those with overweight and obesity, health surely needs to be the primary focus, but why would we go to the trouble of eating differently, being more active, and doing all the hard things that go along with becoming healthier if not for the satisfaction of shopping for new, smaller sized clothing, compliments from long-time friends and family, a feeling of control (finally) over our physical forms, and a sense of well-being that comes with improved health? Weight loss does matter, and “eat less” is a simple message that might resonate, yes, but I fear it is much too simplified and potentially dangerous for those inclined to take it too far. “Eat better” might be a more encompassing message to not only modify caloric intake but to increase the nutritional value of foods we choose. We exercise for fitness. We eat to nourish. Health requires both. Weight loss may not.