Weight train

Yo-yo dieters often lose muscle and gain back fat. Although you burn more calories and stored body fat while doing aerobic exercise, weight training to build muscle is key to maintaining your figure.

Aerobic exercise does boost metabolism, an effect that lasts hours afterward, but muscle burns more calories than fat, even when you're lazing on the couch. A well-rounded fitness routine should include aerobic exercise—at least 30 minutes three times a week, according to Lieberman—plus plenty of strength training.

Snooze to lose

Scientists have discovered that sleep deprivation increases ghrelin, the hunger hormone, and decreases leptin, the hormone that makes you feel full. The end result: You can't stop your cravings for high-calorie, high-carbohydrate foods.

Plus, sleep helps lower levels of cortisol—the stress hormone that leads to “beer gut” syndrome. Get at least eight hours of z's each night to keep your body humming along.