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FEATURED STUDIES |
EAT:
A study determining how your body weight today impacts your health in the future.
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DAPA:
A study looking at the impact of an investigational medication on how your body uses sugar and insulin. |
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 The latest health news is a surprise: “Exercise won’t make you thin.”
That Time magazine cover story appeared following a visit by one of its reporters to our campus. So, I feel compelled to offer a correction to a story that drifted off course to the conclusion that exercise is not useful for weight loss and weight management. Granted, exercise and its benefits can be a complex story. Even our own scientists discuss the relative importance of eating less or exercising more to lose weight and keep it off. To use a journalistic term, these findings would make interesting “sidebars” to a main story. However, to conclude that exercise is “useless” in the management of body weight is sending an unhealthy message. Most scientific evidence based on animal and human studies shows that regular exercise is a critical component of weight loss and weight control. Right now, only about five-percent of the U.S. adult population meets the current national recommendation of 30 minutes of moderate intensity exercise five days a week, when exercise level is objectively measured. So any story that discourages exercise is counterproductive. The Time article raised three issues to incorrectly conclude exercise won’t help you lose weight.
First issue - eating less is really the only way to lose weight. Yes, it is obviously easier to eat less than to exercise more. But many individuals have successfully lost weight simply by increasing exercise. It can be done. The physiology is real. Bodies stay at the same weight when a caloric balance is achieved. Under controlled laboratory conditions we see that when the amount of calories eaten equals calories used by activity and exercise, then weight remains the same. Participants lose weight when they use more calories than they eat and gain weight when they eat more calories than they use up. That means the body doesn’t care whether it loses calories by eating less or exercising more, the response is the same; weight is lost. So a diet in which you cut 300 calories a day will have more or less the same effect as activity that expends 300 extra calories a day. So, it may be easier to reduce your calories by eating less than by exercising more, but this does not mean exercise is “useless.” In fact, we gain many other health benefits by exercising, like lower blood pressure and a healthier heart and cardiovascular system.
Second issue - people succumb to so-called dietary compensation, meaning that after exercising, we get hungry and eat more, or “reward” ourselves with a snack. The fact is that millions of regularly active people tend to be normal weight. They may eat more, but it equals their level of energy expenditure. For instance, elite athletes in physically demanding sports may consume on a regular basis more than 5,000 calories per day and yet be quite lean and muscular. For the general public, we should base the main message on the preponderance of the evidence, which says that if you exercise regularly you will increase your caloric intake to meet the demand of your physically active lifestyle. I know of no credible evidence demonstrating that people overindulge in food just because they engaged in a bout of exercise. Such people can undoubtedly be found, but it is a small minority among those who engage in exercise. In the aggregate, we know of no study that concludes exercise causes enough overeating to increase body weight and reverse the health benefits. However, we do know that appetite is typically depressed after a bout of vigorous exercise. As a matter of fact, regular exercise is one of the most efficient ways to help keep caloric intake at the right level for you.
Final issue - those who exercise regularly may offset the effort by reducing their other daily activity and thus expend fewer calories than expected. This particular issue is complex as there are considerable individual differences in post exercise behavior. There are a few studies on both sides of this issue, but on balance more studies show that such compensation does not occur. Ironically just as the TIME issue came out, a group of researchers from Duke University published results showing daily exercise did not lead to a decrease in other activity for the remainder of the day.
Despite the confusion caused by the latest headline, we should rely on the vast majority of evidence that shows moderate activity or exercise should be part of any plan to lose weight, keep it off, and become healthier.
Claude Bouchard, Ph.D.
Executive Director
Pennington Biomedical Research Center
Baton Rouge, LA
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