Diabetes Forecast

Workouts and Weight

Learning why some people drop pounds with exercise—but others don’t

Marc-Andre Cornier, MD
Photograph by Julia Vandenoever

Marc-Andre Cornier, MD

Endocrinologist, University of Colorado School of Medicine


ADA Research Funding
Translational Science

It’s an old story: Two people go to the gym hoping to lose weight. They do the same workouts with the same dedication—but while the pounds melt off one, the other can’t seem to shed an ounce. Talk about frustrating.

Clinicians have long known what the trainer at the gym may be reluctant to tell you. Exercise alone usually doesn’t lead to weight loss—in fact, for most people it may be far less effective than going on a diet.

That’s because the body works hard to preserve pounds in the face of exertion. In most cases, as people burn more calories, the body employs a variety of strategies to replenish them—from increased appetite to a slowed metabolism.

“People are burning more calories than they’re consuming, but their bodies are telling them to eat more. Then they don’t lose weight,” says Marc-Andre Cornier, MD, an endocrinologist at the University of Colorado School of Medicine. “People compensate for the lost calories—and maybe overcompensate. And some individuals reward themselves for exercising.”

From an evolutionary point of view, that response was appropriate. Tens of thousands of years ago, life was feast or famine. It made sense to pack on the pounds when food was available because it was hard to know when you might be lucky enough to catch your next meal.

Today, though, the problem is an overabundance of calories. “Overconsumption might have been good a long time ago when you had to spend a lot of time chasing your food,” Cornier says. “But in our day and age, we have more than enough food around us.”

That reality means most weight-loss programs emphasize the diet part of the “diet and exercise” formula. “There’s a common perception that exercise isn’t a good tool to help people lose weight,” says Cornier. “For many, exercise alone, without dietary intervention, isn’t going to help.”

And yet for some, it’s possible to keep eating normally and lose weight through exercise alone. “There are some people who exercise and it makes them less hungry,” he says.

With the help of a grant from the American Diabetes Association, Cornier is trying to figure out why these evolutionary misfits respond so well to exercise. “Our goal is to understand the variation of response—why do some people lose weight with exercise and some don’t?” he says.

He already has some clues that the differences may be hardwired in the brain. In a pilot study, Cornier put patients in an MRI, a machine that looks at brain activity, and showed them pictures of food to see what part of their brain turned “on” or “off.” Then they were put through a six-month exercise program. “The people who lost the most weight had more turning off in these brain regions,” he says.

In his latest experiment, Cornier is putting a group of 60 people through a battery of tests, from MRIs to old-fashioned surveys about diet and lifestyle. Participants also spend three days eating whatever they want to give Cornier and his collaborators a sense of their baseline appetite.

Then they’re all assigned to a rigorous, five-days-a-week exercise program. After three months, there’s a weigh-in. By comparing people who lost weight with people who didn’t, Cornier hopes to pinpoint what set them apart at the outset. Understanding from the start who responds best to exercise—and who’s unlikely to lose weight from working out alone—would be a huge step forward. “If we could predict that, we could really target the right intervention for the right patient,” Cornier says.

In the meantime, Cornier is cautious not to discourage anyone from working out, especially because exercise—regardless of weight loss—is so important for overall health, including heart health and blood glucose management. “I would never want to tell people not to exercise—there are so many reasons to promote exercise,” he says. “But if the goal is weight loss, I emphasize diet because it’s more impactful in a lot of folks.”

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