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 Dr. 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.
"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 Dr. Barbara J. Rolls, who directed the study and who holds the Helen A. Guthrie Chair of Nutritional Sciences at Penn State.
Ello-Martin said that the study showed 'choosing foods that are low in calorie density helps in losing weight, without the restrictive messages of other weight loss diets'.
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 dieticians 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.
The findings appear in the June 2007 issue of the American Journal of Clinical Nutrition.