Some experts claim exercising before you eat primes the body to burn more fat. Others, such as TV fitness expert Jillian Michaels, say, “This is a big, fat lie. Starving yourself before exercising can actually be detrimental to your body.”

Also, while not eating before exercising might burn more fat, burning fat differs from losing fat. This is because to lose fat you must create a calorie deficit by eating fewer calories than you use.

Indeed, the biggest disadvantage to exercising on an empty stomach is you may not have enough energy to get through a workout. This is why Boston-area sports nutritionist and member of the American College of Sports Medicine Nancy Clark, MS, RD, encourages her clients to fuel up with a little pre-exercise food to enhance performance and, thereby, their ability to burn more calories.

Michaels agrees with Clark. “I’m not suggesting you pig out,” she says. “A small healthy snack consisting of carbohydrates and protein will properly fuel your body for a killer workout.”

“Each person has a different tolerance for pre-exercise food,” says Clark, author of the Sports Nutrition Guidebook. She suggests folks choose a small (100- to 300-calorie) snack, such as “a few pretzels, crackers or other fuel that will enhance stamina, endurance and enjoyment of exercise.”
Still, experts also suggest that since you know your body best, do what works for you.