Effects of fat intake on weight loss

Several lines of evidence suggest that different food sources of calories may have different effects on metabolic processes and fat deposition. Dietary fat appears to be more fattening than dietary carbohydrate because it may be converted more readily to adipose tissue and requires less energy to metabolize. Little is known, however, about the effects of variations in dietary fat intake on weight loss during a calorie-restricted diet. Criticism has been leveled at the only previous study to evaluate this subject, because the protein content of the various test diets was not kept constant and because no exercise program was included in the weight-loss regimen.

In a new study conducted at Brigham Young University, the effects of varying fat content were evaluated in the context of a weight-loss program that included both diet restriction and supervised exercise. Forty-eight obese premenopausal women were randomly assigned to 1,200 kcal test diets with 10, 20, 30, or 40% of calories from fat. The protein content of all of the test diets was held constant at 20%, and subjects followed the test diets for 12 weeks, while participating in a structured exercise program five days each week.

There were no significant differences among any of the four dietary treatment groups in the amount or rate of weight loss or in the percent of body fat lost during the 12-week treatment period. The authors conclude that diet composition has little, if any, effect on the loss of body weight or body fat during short-term obesity treatment. This conclusion is consistent with the findings of the one previous study that investigated this topic. The authors speculate that a 12-week period may be too brief to detect effects of diet composition on weight loss or that diet composition may be important only when energy intake exceeds energy expenditure, not when energy balance is negative, as it is on a weight-loss regimen.

John J Powell, Larry Tucker, A Garth Fisher, and Kim Wilcox, The Effects of Different Percentages of Dietary Fat Intake, Exercise, and Calorie Restriction on Body Composition and Body Weight in Obese Females, American J Health Promotion 8(6):442-448 (July/Aug 1994) [Reprints: Larry Tucker, Phd, 237 SFH, Brigham Young University, Provo UT 84602!