The common wisdom is that you can't out-train a poor diet. One reason is that exercise can lead to an increased appetite, causing you to eat back a majority of the calories you just burned.
But with enough exercise, around 300 minutes a week, you can lose weight and reduce body fat, according to a study published in Medicine & Science in Sports & Exercise.
Researchers from the University of Kentucky looked at 44 overweight, sedentary participants between the ages of 19 and 49 as they embarked on 12-week exercise programs.
One group was assigned to exercise for six days a week for about 40 minutes to an hour a day, another group exercised twice a week, and the final group maintained its typical inactive routine.
While both exercising groups, on average, lost a small amount of total weight, the frequent exercisers lost significantly more body fat.
Researchers found that the exercise increased participants' appetite by boosting hormones that prompt you to eat. However, the 300 minutes a week burned enough calories to offset the post-workout snacks, they concluded.
Working out can increase appetite to help your body compensate for calories burned
Exercising for about an hour a day, six days a week, burned an average of 2,750 calories, based on calculations from the heart rate monitor participants wore.
While the group that worked out twice a week also burned around 1,500 calories and logged an average of 90 minutes per session, their weight and fat loss was stymied.
That's due to a phenomenon called compensation, according to researchers. If you've ever exercised intensely and felt ravenous afterward, you're familiar with this — when the body burns more calories than it consumes (an energy deficit), it can respond by increasing the hormones that make you feel hungry.
That can cause you to consume around 50% of the calories you just burned off, in the form of post-workout meals and snacks, according to previous work from this research team, or around 1,000 extra calories a week.
In this study, both exercising groups experienced compensation. The group exercising six times a week had a slightly bigger appetite and ate more extra calories than the group that exercised twice. But all those extra minutes of exercise helped them maintain a calorie deficit, which lead to weight loss and reduced body fat.
Exercise has benefits beyond immediate weight loss
But weight loss is incredibly complicated, and this study had a few important limitations.
For instance, the study defined exercise as deliberate physical activity for the purpose of improving health or losing weight. As a result, it didn't include some daily calorie-burning activities like walking or cleaning, since they weren't part of a workout.
Those milder forms of exercise can have major health benefits, including lower risk of disease. They can also help with weight loss when combined with the right diet.
Deliberate exercise has some bonus benefits, too. More vigorous forms of exercise, such as strength training, can help you build muscle. As your strength and endurance improves, you're able to put more work into your workouts, increasing the calorie burn as the intensity goes up. Those extra muscles have an additional benefit of burning more calories even while you're resting, too, so your overall metabolism increases slightly as you put on lean mass.
Finally, exercise is linked to a ton of positive changes that have nothing to do with your weight, including better mood, improved sleep, and a longer lifespan. These are all good reasons to hit the gym whether you're on a diet or not.
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