About 11 percent of U.S. adults—roughly 28 million Americans—are now taking GLP-1 medications for weight loss, according to a recent Gallup poll.
The drugs have transformed conversations around obesity, appetite, and metabolism. Lost in much of the dialogue, however, is how these drugs should fit into a broader approach to physical health and exercise. Separately, as demand surges, new debates have begun to unfold over who should pay and have access—with insurers, employers, and policymakers grappling with whether to cover these medications.
Daniel Lieberman, Lerner II professor of biological sciences in the Department of Human Evolutionary Biology and the director of undergraduate studies, has spent decades studying how the human body evolved to move, eat, and adapt to its environment.
In this interview, edited for length and clarity, Lieberman explains what the rise of GLP-1s reveals about the mismatch between human biology and modern lifestyles in countries like the United States, and why, even with weight loss drugs, exercise remains essential.
1. From an evolutionary perspective, what do GLP-1s reveal about the mismatch between our biology and modern environments?
For most of our evolutionary history, human beings had to work hard to obtain and eat whatever they hunted, gathered, or grew. There were no industrial farms, factories, or supermarkets. Now, the average American supermarket offers about 40,000 food products—many industrially processed to be appealing, convenient, and affordable.
Many of these foods have little to no fiber (removed because it goes rancid), abundant added sugar, fat, and salt in just the right proportions to light up our brains; and they are often enhanced and stabilized with potentially harmful chemical additives. Combined with declining levels of physical activity, this food is evolutionarily mismatched for human health.
As a result, three out of four Americans are diagnosed overweight or obese, and over the last few decades, there has been a rise in the prevalence of many chronic conditions that used to be less common—such as type 2 diabetes, coronary heart disease, and some cancers.
Enter GLP-1s. These drugs have numerous effects, but the one most benefiting dieters is appetite suppression. GLP-1 users often report they stop craving many foods and can bypass the hunger that otherwise comes with eating fewer calories than one spends. For some (not everyone), and depending on [the] dose and which drug they take, GLP-1s have enabled dieters to lose as much as 25 percent of their former weight as well as improve their metabolism.
As someone interested in improving human health, I’m excited about the potential of GLP-1s. But as an evolutionary biologist, I am saddened that we need them. Wouldn’t it be better if we filled our supermarkets with inexpensive, convenient, appealing, healthy foods that don’t promote obesity?
2. Can you share any evolutionary science behind healthy habits for exercise?
Broadly speaking, we evolved to engage throughout our lives in two major categories of physical activity. The first is aerobic (or cardio) physical activity that involves sustained movement for prolonged periods of time, thus causing our hearts to pump more blood more rapidly throughout our bodies. The second is strength (or resistance) physical activity,which involves generating high amounts of muscle force against an external load.
Both stimulate repair and maintenance processes that build capacity, slow aging, and reduce disease risk. Without regular physical activity, those processes are activated less often, accelerating loss of function as we age.
3. How do you think these drugs should fit into a broader approach to physical activity and long-term health?
We don’t yet know how GLP-1s affect dieters’ abilities and motivations to exercise. On the one hand, because being overweight or obese can make exercise difficult or unpleasant,weight loss from GLP-1s has the potential to increase one’s capacity to exercise. On the other hand, weight loss from reduced energy intake on GLP-1s can increase fatigue, making exercise more challenging.
In addition, while weight influences wellbeing, and there are many benefits to losing weight, we too often conflate weight too strongly with health. This is especially concerning in terms of strength training, because GLP-1s cause high levels of muscle loss—putting GLP-1 users at increased risk of frailty as they age. It also comes with potential side effects,such as nausea and diarrhea.
4. What benefits does exercise provide beyond weight management?
Lifelong physical activity has so many diverse benefits, it’s hard to know where to start. Exercise improves mood, helps relieve stress, and benefits sleep. It lowers levels of chronic inflammation, hence various health concerns caused by inflammation such as atherosclerosis (hardening of the arteries), type 2 diabetes, and osteoarthritis. Exercise reduces the risk of Alzheimer’s disease and other forms of dementia, helps prevent high blood pressure, lowers the risk of many cancers, and helps prevent and treat major depressive disorders. Additionally, it boosts the immune system to help fight infectious diseases. Altogether, exercise stimulates so many beneficial effects it will never be possible to replace it with a pill.
5. Looking ahead, do you have concerns about how GLP-1 medications may change the way we think about obesity, diet, and exercise?
GLP-1s are game-changing drugs, but they represent some tradeoffs. They may not necessarily help people eat healthier foods, and they don’t prevent weight gain in the first place.I worry that GLP-1s will reinforce a feedback loop I call dysevolution, in which we treat the symptoms rather than the causes—thus making us permanently dependent on these drugs. Indeed, studies find that when people quit GLP-1s, their appetite typically comes roaring back, and they regain much of the weight they lost.
Will GLP-1 users have to take these drugs for the rest of their lives? Will GLP-1s cause more people to exercise even less? And perhaps most importantly, will our enthusiasm for GLP-1s dampen the urgent need to improve our food system so people don’t need them?
