Low-Carb Diet Research and News

Feeling full on fiber can cut calories

By Nanci Hellmich, USA TODAY

Nutrition researcher Barbara Rolls has a theory that she believes will help dieters lose weight while controlling hunger.

She says people may feel full on fewer calories by adding fiber-rich or water-filled fruits and vegetables to standard recipes and menu plans. That way, people can eat the same-size portion they'd normally eat, but it will contain fewer calories.

Translated into practical terms, that might mean selecting grapes instead of raisins as a snack or adding eggplant to lasagna, blueberries to pancakes, mushrooms, celery and extra tomatoes to chili, and sprouts, lettuce or tomato to sandwiches.

"The bottom line for weight loss is you have to eat fewer calories than your body needs," says Rolls, a professor of nutrition at Pennsylvania State University. "But hunger - whether psychological or physiological - often sabotages most diets. Feeling full depends on eating a satisfying amount of food, and often tiny portions don't do it."

In her new diet book, Volumetrics (HarperCollins, $24), written with Robert Barnett, Rolls tries to teach people how to choose foods that help control their hunger while providing fewer calories. The book includes recipes and menu plans.

Studies done by Rolls and others show that over the course of a day or two, a person eats the same weight of food. So she recommends that people eat the usual amount of food but lower the calories in each portion by cutting the energy density, or calories per gram. Decreasing the foods that are high in fat and increasing those high in water will lower the energy density of the diet.

Rolls and her colleagues have shown that when people eat meals modified to have fewer calories in a portion and can eat as much as they want, they consume about 400 fewer calories a day and feel just as full.

In one study, women who ate a lower-energy-density soup as a first course ate fewer calories overall during lunch. Other water-rich foods include fruits, vegetables, cooked grains and stews.

Rolls says her research helps explain why some people who switch from high-fat to fat-free foods don't lose weight. In a struggle to feel full, they eat too much of the fat-free food.

"Cutting fat only helps if it lets you lower the energy density of your eating pattern," she says. "For example, an ounce of cheddar cheese and an ounce of fat-free pretzels have about the same energy density, and thus the same number of calories. So switching from cheese to pretzels won't help to cut calories."

But that's not as likely to happen with fiber- and water-rich foods, because you get more bulk for the calories. "Switching to, say, apples or oranges, full of fiber and water and low in energy density, can make a difference."

A high-fat diet promotes weight gain because it's high in energy density. Just cutting fat won't help you lose weight unless you also limit low-fat, fat-free foods that are high in energy density.

Some of Rolls' tips for lowering the energy density of your diet:

Eat fruit with breakfast -- half a grapefruit, an orange, an apple or a banana. Make a fruit salad with two or more of your favorite fruits.

Top cereals, pancakes and waffles with fruits such as peaches, blueberries, strawberries and raspberries.

For a snack, choose fresh fruit rather than dried fruit or baked or fried foods. Add vegetables such as zucchini, yellow squash, peppers, onions, eggplant and spinach to pasta dishes, casseroles and pizza.

Add extra vegetables to sandwiches.

Increase the proportion of vegetables in stir-fry dishes, fajitas, broth-based soups and stews.

Start lunch or dinner with a bowl of broth-based soup. Include a tossed green salad or fruit salad with dinner.

Choose desserts with fruit.

Critics of Rolls' plan say it won't be the answer to everyone's weight woes. The energy-density idea "is a hard concept to get across to people. The bottom line is calories," says John Foreyt, obesity expert at Baylor College of Medicine in Houston.

Chris Rosenbloom, associate professor of nutrition at Georgia State University in Atlanta, says that because so many people eat out and don't cook that much, it will be difficult to follow some of the advice in the book.

Also, she believes that people really need to watch their portion sizes, which are often much too large, to lose weight.

On the other hand, she says, Volumetrics is "a good alternative to the rage of high-protein, high-fat diets. It incorporates fruits and vegetables into the diet and is science-based."

In the book, Rolls says there are other keys to weight loss, including keeping a food and exercise log, having a support group with family or friends, exercising, managing stress in ways other than eating, and learning to cope when you overeat.

Rolls says that changing behavior is crucial, but it isn't easy. If you are 40 years old and regularly eat five meals and snacks a day, you've done so 70,000 times, she says. It takes a lot of behavior modification to change that.

"People say - and some research shows - that the hardest habits to change are your eating habits," Rolls says. "You learn eating habits at a very early age, and to expect people to substitute carrot sticks for ice cream is not realistic. They have to learn ways to eat within their established eating habits."