RODALE NEWS, EMMAUS, PA—To eat or not to eat…before a workout: It's a question that has perplexed gym rats for years, ever since Bill Phillips suggested in his 1999 bestseller Body for Life that exercising on an empty stomach would speed up fat burn. The idea is that not eating before exercise forces your body to shift from quick burning carbohydrates (which you usually get from food) as a source of fuel to the fat stores you want to burn off. But that argument doesn't hold water, says Brad Schoenfeld, MS, CSCS, president of Global Fitness Services, a consulting firm, and professor in the department of exercise science at Lehman College in New York. "It's a shortsighted way of looking at how your body works," he says.
THE DETAILS: In an article published in this month's issue of Strength and Conditioning Journal, Schoenfeld analyzed the research that's been conducted on how our bodies function during exercise and concluded that, whether you eat or don't eat before exercise, research shows your body burns the same amount of fat. And working out on an empty stomach can actually cause muscle loss, he adds, if you do it on a regular basis. When you're hungry, your body goes into survival mode and draws protein away from muscle, where it's less crucial to survival, than from your kidneys and liver, where the body normally looks for protein. "Your body cares more about survival than looking good at the beach," he says. As a result, you lose muscle mass, which can, over time, suppress your metabolism and make it harder to lose weight.
On a more basic level, he says, exercising on an empty stomach means you don't have the energy to put in a really good workout. "One of the benefits of aerobic exercise is doing it at a higher intensity," he says. "If you're just getting out of bed, slogging through your exercises like a zombie, you won't be able to get that intensity."
WHAT IT MEANS: Tempting as it may seem to cut down on calories before you head into a big calorie-burn session, you're not doing yourself any favors. You aren't giving yourself the fuel you need to last through a 30-minute or hour-long workout, and you could be losing muscle mass while you're at it. "You're just spitting in the wind," jokes Schoenfeld.