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.