Pop quiz: Two women go walking. One finishes quickly; the other takes her time. They each burn about 400 calories. So who sheds more belly fat? The obvious answer: It's a tie. But a surprising new study shows that the one speed walking actually loses more.

Researchers from the University of Virginia found that women who did three shorter, fast-paced walks a week (plus two longer, moderate-paced ones) lost 5 times more belly fat than those who simply strolled at a moderate speed 5 days a week, even though both groups burned exactly the same number of calories (400) per workout. Those speed walking also dropped more than 2 inches from their waistlines, pared about 3 times more fat from their thighs, shed 4 times more total body fat, and lost almost 8 pounds over 16 weeks--all without dieting!

The improvements didn't stop there. The high-intensity exercisers lost about 3 times more visceral fat--the dangerous belly fat that wraps around organs such as the liver and kidneys and has been linked to diabetes, heart disease, and high blood pressure. "Vigorous exercise raises levels of fat-burning hormones," says lead researcher Arthur Weltman, PhD, director of the exercise physiology laboratory at the university. It also increases afterburn (the number of calories your body uses postexercise as it recovers) by about 47% compared with lower-intensity workouts.

So how do you make all this science work for you? Start with our 8-week progressive walking plan, which includes both shorter, high-intensity workouts and longer, moderate-paced ones. Add in the Flat Belly sculpting moves to firm your ever-shrinking middle. In just 2 months, you could walk off 1 or 2 sizes--without dieting!

Then celebrate your success by walking a full or half-marathon. The 8-Week Plan  will prime you for the challenge while flattening your belly.