Calorie density key to losing weight

University Park, Pa. -- Eating smart, not eating less, may be the key to losing weight. A yearlong clinical trial by Penn State researchers shows that diets focusing on foods that are low in calorie density can promote healthy weight loss while helping people to control hunger.

Foods that are high in water and low in fat -- such as fruits, vegetables, soup, lean meat, and low-fat dairy products -- are low in calorie density and provide few calories per bite. "Eating a diet that is low in calorie density allows people to eat satisfying portions of food, and this may decrease feelings of hunger and deprivation while reducing calories," said Julia A. Ello-Martin, who conducted the study as part of her doctoral dissertation in the College of Health and Human Development at Penn State.

Previously, little was known about the influence of diets low in calorie density on body weight. "Such diets are known to reduce the intake of calories in the short term, but their role in promoting weight loss over the long term was not clear," said Barbara J. Rolls, who directed the study and who holds the Helen A. Guthrie Chair of Nutritional Sciences at Penn State.

"We have now shown that choosing foods that are low in calorie density helps in losing weight, without the restrictive messages of other weight loss diets," explained Ello-Martin, whose findings appear in the June 2007 issue of the American Journal of Clinical Nutrition.

The researchers compared the effects of two diets -- one reduced in fat, the other high in water-rich foods as well as reduced in fat -- in 71 obese women aged 22 to 60. The participants were taught by dietitians to make appropriate food choices for a diet low in calorie density, but unlike most diets, they were not assigned daily limits for calories.

At the end of one year, women in both groups showed significant weight loss as well as a decrease in the calorie density of their diets. However, women who added water-rich foods to their diets lost more weight during the first six months of the study than those who only reduced fat in their diets -- 19.6 pounds compared to 14.7 pounds. Weight loss was well maintained by subjects in both groups during the second six months of the study.

Records kept by the women showed that those who included more water-rich foods ate 25 percent more food by weight and felt less hungry than those who followed the reduced-fat diet. "By eating more fruits and vegetables they were able to eat more food, and this probably helped them to stick to their diet and lose more weight," said Ello-Martin.

"Choosing foods that are low in calorie density helps to control hunger and is a healthy strategy for losing weight over the long term," said Rolls. Practical information on incorporating foods with a low calorie density in daily diets can be found in Rolls' books "The Volumetrics Eating Plan" (2007) and "The Volumetrics Weight-Control Plan" (2000).

The Penn State researchers added that increasing the consumption of water-rich foods such as fruits and vegetables is not only in tune with current dietary guidelines, but also may help reduce the risk of chronic illnesses.

Other researchers in the clinical trial, which was funded by the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health, include Liane S. Roe, research nutritionist; Jenny H. Ledikwe, post-doctoral research fellow; and Amanda M. Beach, study dietitian, all at Penn State.