UNIVERSITY PARK, Pa., June 8 -- Eating more water-rich foods, especially fruits and vegetables, fats helped women drop more pounds than simply moderating fat intake.
That's what Barbara J. Rolls, Ph.D, and colleagues at Penn State University, here, found when they put 97 obese women (body mass index in kg/m2 from 30 to 40) on diets.
The women, ranging in age from 20 to 60, were randomly assigned to groups that were counseled either to reduce their fat intake or to reduce their fat intake and increase their intake of water-rich foods, which are low in energy density (kcal/g). They were given no calorie restrictions.
Both weight-loss strategies were accompanied by an increase in physical activity focused on walking with a pedometer, and both were successful, but women on the low energy-density diet lost more weight, despite eating more food, by weight, and eating at will, the authors wrote in the June 1 issue of the American Journal of Clinical Nutrition.
Their findings support the idea that people who eat nutritionally balanced diets that are high in water content will feel fuller longer, and thus have a greater chance of losing weight, the authors wrote.
"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. Rolls, a professor of nutritional sciences.
Women in each group received the same amount of instruction on fat reduction, behavior change, physical activity, and the principles of their diets, and within each group they were taught to make food choices that were reduced in energy density and appropriate in portion size.
"Neither group was given daily limits for energy or fat intake; the subjects were instructed to eat ad libitum amounts of food while following the principles of their assigned diets," the authors noted.
Overall the 71 patients who completed the one-year study (35 in the reduced fats plus fruits and vegetables group, and 36 in the reduced fat alone group) had significant decreases in body weight (P<0.0001).
Women in the fruits-and-vegetable group lost 33% more weight during the first six months of the trial than women in the reduced-fat only group (8.9 + 0.8 kg, or 19.6 +1.8 lb, compared with 6.7 + 0.7 kg, or 14.7 + 1.5 lb P=0.034). During the second six months of the trial, however, there were no significant differences in the pattern of weight change.
In the second six months of the study, when contact with the participants was less frequent by study design, the authors found that women in both groups were successful at keeping the weight off. In each group, the participants regained only 0.7 + 0.4 kg (1.5 +0.9 lb).
At the end of the trial, the mean weight loss in the fruits-and-vegetables group was 7.9 + 0.9 kg (17.4 + 1.9 lb); it was 6.4 + 0.9 kg (14.1 + 1.9 lb) in the reduced-fat-only group.
An analysis of diet records showed that while both groups had similar reductions in fat intake, the women in the water-rich-foods group consumed significantly fewer kcal/g (P =0.019), while eating significantly more food, by weight (P=0.025). That was especially true for women who ate more fruits and vegetables than, say, soups (P=0.037).
Women who ate more fruits and vegetables also reported feeling significantly less hungry, the authors noted.
"Diets that are low in energy density, particularly those that encourage increased consumption of water-rich foods, allow individuals to eat adequate amounts of food while restricting energy intake, which helps to control hunger," they wrote.
"Because a wide variety of foods can be included in a diet that is reduced in energy density, this type of eating plan can be adapted to individual food preferences. Individuals should be encouraged to find a low energy- density eating pattern that is nutritionally balanced and can be sustained for lifelong weight management," they concluded.
The authors acknowledged that there were no significant between-group differences in reported energy intake that corresponded with the differences in weight loss, which could be explained by wide variations in daily energy intake. They also noted the possibility of reporting bias by the patients, although they pointed out that the degree of underreporting was likely to be similar between the groups.
The study was supported by the National Institutes of Health. No conflicts of interest were listed.Primary source: American Journal of Clinical NutritionSource reference: Ello-Martin JA et al. " Dietary energy density in the treatment of obesity: a year-long trial comparing 2 weight-loss diets."
Am J Clin Nutr 2007 85: 1465-1477.
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