WEDNESDAY, May 9 (HealthDay News) -- Want to lose weight? Focus on reducing the "energy density" of your diet, a new study suggests.

In simple terms, that means eating foods that contain a lot of water and relatively few calories per portion, such as fruits, vegetables, and low-fat dairy products. What's more, that approach can help you lose more weight than if you don't eat those foods. And if you reduce the energy density of your diet, you actually get to eat more, at least in volume, the study authors said.

"The energy density of food refers to calories per gram," said Barbara Rolls, a professor of nutritional sciences at Pennsylvania State University, and a coauthor of the study.

"Energy density goes from zero to nine," Rolls said, adding that water has zero density while fat, which has 9 calories per gram, has a density of nine.

Fruits, vegetables, low-fat foods and water-rich foods such as soups all have low energy density, she said.

The simplified weight loss tip that springs from the study: "Increase the water content of foods you eat and decrease the fat content," Roll said. This premise is the heart of her dietary approach called Volumetrics.

In the study, Rolls and her colleagues studied the effects of a six-month intervention for diet and weight loss in 658 healthy adults. They included men and women, average age 50. Their average body mass index or BMI, a ratio of height relative to weight, was 33.6 -- defined as obese.

One group got a single dietary counseling session; the other two groups each got 18 sessions. The subjects who were counseled were told either to increase physical activity and reduce energy intake or were told that advice, plus advice on a special diet called the Dietary Approaches to Stop Hypertension (DASH), which emphasizes the consumption of fruits, vegetables and low-fat dairy foods.

All three groups lost weight. But then the researchers wanted to see the exact effect of reducing energy density on weight loss. So they combined all three groups and analyzed their weight loss in relation to how much they reduced their energy density. Those who had the most reduction in energy density lost the most weight -- nearly 13 pounds over six months -- compared to those who reduced their energy density the least -- about 5 pounds.

"Those who ate the lowest energy density diet got to eat 300 grams more of food a day," Rolls said. That's 10.5 ounces more food a day.

The findings are published in the May issue of the American Journal of Clinical Nutrition.

The study results make perfect sense, said Cathy Nonas, director of diabetes and obesity programs at North General Hospital, and assistant clinical professor of medicine at Mount Sinai School of Medicine, both in New York.

Reducing energy density in your diet not only reduces overall calories but boosts the nutritional value of the diet, Nonas said. The only downside? "That kind of food also tends to be the most expensive," presenting a public health dilemma for health-care providers trying to help people of all income levels achieve a healthy weight.

Nonas' suggestion for reducing energy density: "Halve the amount of pasta you eat and double or triple the vegetables. In a restaurant, order extra vegetables." Or choose tomato soup as a first course.

Reducing energy density is one of the suggestions in the federal government's Dietary Guidelines for Americans 2005, both Rolls and Nonas noted.

More information

To learn more about proper dietary guidelines, visit the U.S. Department of Agriculture.

SOURCES: Barbara Rolls, Ph.D., professor of nutritional sciences, Pennsylvania State University, University Park, Pa.; Cathy Nonas, R.D., director of diabetes and obesity programs, North General Hospital, and assistant clinical professor of medicine at Mount Sinai School of Medicine, both in New York City; May 2007, American Journal of Clinical Nutrition

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