Add more fiber to your low fat diet to supercharge the effectiveness of your flat abs program.

High fiber diet benefit # 1: The "fill" factor - Because high fiber diet foods like fruits and vegetables supply plenty of bulk to your meals without adding a lot of calories, they keep you feeling full longer and help you lose weight, according to a study at the Human Nutrition Research Center at Tufts University. Researchers concluded that a low fat diet works only if it’s also a high fiber diet - rich in healthy foods like fruits, vegetables and whole grains, all of which fill you up on fewer calories and less fat. In contrast, a low fat diet that is low in fiber and high in sugar, salt and preservatives can lead to bloating and weight gain.

In a study conducted by Barbara Rolls, Ph.D., a professor at Penn State University and co-author of The Volumetrics Weight-Control Plan (HarperTorch, 2003), subjects who ate vegetables as part of their meals consumed about 100 fewer calories and didn't make up for the caloric deficit later. While saving 100 calories a day may not sound like much, it translates into losing 10 pounds in one year. Use just this one trick — and there goes your tummy!

High fiber diet benefit # 2: The "chew" factor - "High-fiber foods require more chewing and take longer to eat," explains Leslie Bonci, M.P.H., R.D., author of the American Dietetic Association Guide to Better Digestion (John Wiley & Sons, 2003). "Because your mouth is more involved in the eating of high-fiber foods, you feel more satisfied with a high-fiber meal."

How to add fiber to your diet comfortably - It's important to add fiber slowly but consistently to prevent gas. "Make higher-fiber choices throughout the day; don't have all your fiber in one bunch," Jenkins says. "This is particularly important with viscous fiber — a type of soluble fiber found in beans, oats and barley that also has the benefit of lowering blood cholesterol," he says.

For best results, increase your fiber intake slowly over the course of one month and drink plenty of water to keep food moving through your system as quickly as possible.

Read on for diet tips about healthy carbs and their role in your flat abs.