The study found that obese and prediabetic men and women who exercised while dieting improved their insulin sensitivity twice as much as people who dieted alone, even though everyone lost amounts of comparable weight.
“These results demonstrate that regular exercise during a diet-induced weight loss program has profound additional metabolic benefits” over dieting itself, the study authors write.
Researchers behind the study said they hope the results will motivate dieters to exercise, including people who have been prescribed popular new medications, such as Ozempic, to losing weight.
“Exercise should absolutely be on the agenda” whether someone uses medications or not, said Samuel Klein, chief of the division of geriatrics and nutritional science at the University of Virginia School of Medicine. Washington in St. Louis and lead author of the study. .
The experiment was small, involving just 16 men and women in total, but the results reinforce a growing scientific consensus that being physically active while cutting calories changes our bodies in ways that dieting does. alone cannot match.
Does exercise help you lose weight?
“It’s reasonable to ask” whether we should bother exercising while losing weight, Klein said. After all, the relationship between exercise and weight is notoriously difficult. “People are told to become physically active if they plan to lose weight,” Klein said. But for the most part, “physical activity does not affect body weight much.”
In fact, exercise alone, without dieting simultaneously, rarely results in substantial weight loss. many studies show, and sometimes leads to weight gain. Exercise generally burns fewer calories than expected. Walk for 30 minutes and you’ll burn about 150 calories, which is easily replaced by a cookie or sports drink. Exercise also often increases appetite.
Overall, Klein said, it’s “easier to cut calories” for most people than to start exercising to lose weight.
Research does, however, offer new evidence on the benefits of exercise when trying to lose weight, even if it does not accelerate or increase weight loss.
The Nature Metabolism study used data from several existing weight loss experiments. In one, eight sedentary men and women with obesity and prediabetes began a supervised, low-fat, “plant-based” diet. All meals were provided and individualized, so each person slowly lost 10 percent of their body weight.
A second group of eight men and women with obesity and prediabetes were given the same meals, but also began exercising six times a week. Four of these sessions were supervised and included approximately one hour of moderate aerobic exercise, such as brisk walking on a treadmill, twice per week; resistance training once a week; and interval training once a week. The other two days, the participants trained alone at home.
The researchers adjusted the participants’ meals to keep their weight loss similar to that of the other group, but the calories involved were few, Klein said.
The program lasted until each person weighed 10 percent less, which took most of them about five months. Before and after, researchers drew blood, biopsied muscles, collected fecal samples, and checked insulin sensitivity, fitness, and other health measures.
Helping people who lose weight be twice as healthy
In the end, both men and women in the diet-only group were leaner, with better cholesterol profiles and other markers of better metabolic health. Perhaps more importantly, their insulin sensitivity improved markedly.
“We expected them to be healthier,” Klein said, “and they were.”
But the scientists were surprised by the practitioners.
This group’s insulin sensitivity gains were twice as great as those of the dieters. They also showed higher numbers of new blood vessels and mitochondria in their muscles. Mitochondria are tiny organelles that power our cells, and the more we have, generally, the better.
Users also increased their muscle strength by around 13 percent and their endurance by 10 percent. The dieters, on the other hand, were now about 2 percent weaker and 6 percent less fit than when the study began.
“We wondered what additional benefits the exercise would bring,” Klein said. “We were amazed at how powerful it was.”
The study has caveats, however. The study relied on “a very small sample size,” said John Thyfault, professor and director of the KU Diabetes Institute at the University of Kansas. And all of these volunteers suffered from obesity and prediabetes. It’s not clear whether healthier people’s results would be similar.
The researchers also closely monitored everyone’s diet and exercise, making compliance with the programs “extremely high,” Klein said. But few of us would benefit from such supervision while losing weight, and some of us might feel intimidated by the scope and intensity of the workouts.
“We don’t know at this point whether less exercise would be as effective,” Klein said.
He and his colleagues hope to explore some of these questions in future studies. But based on the evidence already available, if you diet but don’t exercise, he concluded, “you don’t get the full metabolic health benefits, and our study shows that these effects can be deep.
correction
An earlier version of the article referred to Ozempic as a weight-loss drug. Some patients take it to lose weight, but the drug has been approved by the Food and Drug Administration only for type 2 diabetes and other medical problems, not for weight loss. The article has been corrected.
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