Low-Fat Diet Promotes Weight Loss

A recent study of a group of 64 mostly overweight postmenopausal women examined the impact of aggressively reducing dietary fat on body weight over an 8-month period.1 Analysis of the subjects’ customary diets showed that the heavier women (BMI > 27.5) consumed higher-fat diets (36.6% of calories) than the lighter women (BMI < 27.5), who averaged 29.4% fat calories.

There is a lot of data demonstrating fatter Americans eat a greater proportion of their calories from fat than thinner Americans. In this study the subjects were instructed on how to limit fat intake to about 15% of calories in 8 separate 45-minute educational classes led by a registered dietitian for the first 8 weeks. Each study participant also met individually for a total of 3 hours of dietary instruction spread out over the first 6 months of the study. In addition, study participants met once a week for a potluck dinner and got an additional 30-minute group session to provide feedback and reinforcement for continuing on a 15% fat diet. There was no change in physical activity during the study, so any change in body weight would be due to instruction to limit dietary fat intake. Although fat was limited, the participants were not instructed to reduce calories. Even though these were free-living subjects who did not exercise and ate as much as they wanted, the average subject still lost 13.2 pounds after 8 months. It should be noted that the subjects in this study consumed mostly refined carbohydrates and not whole grains, fruits and vegetables. Even so, the average intake of most nutrients monitored in this diet study went up or did not change. However, the intake of vitamin E and omega-3 fatty acids did drop significantly on this very-low-fat diet. The authors concluded, “This study demonstrates that adherence to a very-low-fat diet consumed ad libitum causes weight loss in the 5-10% range and a reduction in body fat.” They also noted that more emphasis on vitamin E and omega-3-rich foods should accompany dietary instruction to reduce dietary fat.By James Kenney, PhD, RD, LD, FACN.