Filling Up With Less.

Byline: Joan Raymond (With Heidi Richter)

Jill O'Nan used to eat just one meal a day. But, as the joke goes, that meal began in the morning and didn't end until she went to sleep at night. As a freelance writer, O'Nan had no set meal schedule. "If McDonald's delivered, I probably wouldn't have left my house," says O'Nan, 45, who has battled the bulge since she was a child.

With her supersize appetite, O'Nan's weight spiraled to 360 pounds. She tried dieting, but nothing worked. O'Nan did some research and stumbled across a little-known book called "Volumetrics" (harpercollins.com ), which promised that she could manage her weight by choosing foods that the program calls "low in energy density," foods that make you feel satiated, or full, but that are also low in calories. She swapped her serving of fast-food fries for an even larger portion of boiled redskin potatoes in a garlic-dill sauce.

She rediscovered her pressure cooker and started to make homemade meals, including soups and chili seasoned with dark chocolate. In four years she shed an impressive 220 pounds. "I never thought I would be able to get to a healthy weight without feeling deprived, miserable and hungry," says O'Nan, who now wears a size 8.

Volumetrics may be the most popular diet you've never heard of. It doesn't have the zing of The Zone or the image of bronzed beauties from South Beach. But it's been gaining currency with nutritionists and dieters alike for its simplicity and the fact that it's backed by recent peer-reviewed studies at a time when other diet plans have been losing favor.

Fighting hunger is the goal of Volumetrics, developed by Barbara Rolls, a professor of nutritional sciences at the Pennsylvania State University. Rolls has researched everything from thirst to portion control. But it's her study of satiety that is giving her street cred with dieters like O'Nan.

What Rolls found is that feeling full is intrinsically linked to certain foods. The nutritional principle behind those foods is called energy density, or ED. It may sound counterintuitive, but foods low in energy density make you feel fuller. Think fruits, soups and vegetables, all of which have high water content, "the secret ingredient" to satiety, says Rolls. (But drinking water alone won't help you feel full; it will only quench your thirst.) Rolls's research shows that a person eats about the same volume, or weight, of food every day. The trick is to fill your plate with low-calorie foods that leave you satisfied.