When most people finish a hard workout, they want a reward--possibly a sandwich, or some pancakes, or maybe even a burger and fries. What they don't want? To not eat anything. And yet, a few recent studies found that moderate intensity aerobic training could actually decrease your appetite or increase your feelings of fullness or satiety. Strange, right? Who doesn't love shoving their face after a big cardio session? In fact, previous research has shown that people who exercise often reward themselves with food, increasing overall calorie consumption, and often sabotaging their weight loss goals. So, what gives?
"Exercise can definitely suppress hunger," says Barry Braun, Ph.D., director of the Energy Metabolism Laboratory at the University of Massachusetts, Amherst, who has co-authored multiple studies on the subject. How, why, and for how long afterward is something researchers are still working out. They do know that workouts trigger changes in the hunger hormone, acylated ghrelin, and the satiety hormones, PYY and GLP-1--though research has yet to establish the exact relationship. (Starving all the time? Here's Why You're Still Hungry--Even If You Just Ate.)
A recent study published in the journal Metabolism found that perceived fullness--both while fasting and after eating--was higher among participants after 12 weeks of aerobic training, but not after resistance training for the same amount of time. And another study out of Brigham Young University revealed that women appeared to be less interested in food on mornings when they walked on a treadmill for 45 minutes than on days they didn't.
But if sweat sessions make you want to eat less, then why aren't exercisers everywhere losing weight like crazy? "In most studies, there is a poor correspondence between appetite and actual food intake," says Braun. In other words, just because you may not feel as hungry as normal, it doesn't prevent you from eating too much after a workout anyway.
"The effect of exercise on appetite will likely vary from person to person," says Paul MacLean, Ph.D., associate professor of medicine at the University of Colorado Anshutz Medical Center, who has also performed research on the subject. And actual food intake may be more influenced by things like wanting to be rewarded for your "work," the social pressure of having burgers and beers with the guys after a game, or simply being in the habit of eating a big breakfast and not holding back when you start to feel full. (Need to resist temptation? Research just revealed that this healthy activity can help.)
"I'm pretty certain the average person greatly overestimates the number of calories burned during physical activity," adds Braun. "Running 40 minutes at a 9 min/mile pace burns about 450 calories, and there are 500 calories in a Starbucks Venti Mocha Frappucino (with whole milk and whipped cream). So it's incredibly easy to negate the weight loss effects of exercise."
The fix: Nix food rewards--treat yourself to a Redbox flick instead--and write down everything you eat into your iPhone for a week. Studies show that simply logging your meals can make you eat less. Don't skip the gym either, says Kym Guelfi, associate professor at The University of Western Australia, and co-author of the Metabolism study. "Exercise gives you benefits that dieting alone cannot, such as increased fitness, decreased stress, and increased muscle mass, which helps you burn more calories and fat at rest." For a plan that only takes 30 minutes, check out Speed Shred, the new follow-along DVD system from Men's Health.