Lessons from the war on dietary fat.

UNLABELLED

Conventional dietary guidelines put forth by health care institutions and providers for the past 40 years have stressed the importance of reducing the amount of dietary fat consumed. Such a diet is purported to mitigate metabolic risk factors and optimize the ability to achieve or maintain a healthy body weight. However, over the past 35 years obesity rates in the United States have risen dramatically though the level of dietary fat consumed by U.S. adults has fallen. This review examines the potential reasons for this paradox. Various meta-analyses, controlled trials, and cohort studies have demonstrated that reducing dietary fat intake provides for very little weight loss unless accompanied by equal or greater reductions in total energy intake. Due to both psychological (e.g., the tendency for people to eat more of what they consider low fat) and physiological (e.g., the low satiety that accompanies carbohydrate intake) factors, reducing total caloric intake while simultaneously reducing fat intake is a difficult challenge. Further, reductions in total carbohydrate intake, increases in protein intake, and adoption of a Mediterranean diet seem to be more effective in inducing weight loss than reductions in fat intake. Traditional claims that simply reducing dietary fat will improve metabolic risk factors are also not borne out by research. There is some evidence that replacing dietary saturated fat with unsaturated fat may improve metabolic risk factors, but that research is not conclusive.

TEACHING POINTS

• Over the past 40 years, Americans have decreased the percentage of calories they get from dietary fat while rates of overweight and obesity have risen dramatically. • It appears that a decrease in total dietary fat in ad libitum diets may induce a very small decrease in body weight. • Evidence suggests that reductions in total dietary fat intake often occur in conjunction with an increase in total caloric intake. • It seems reasonable to conclude that guiding the public to simply reduce dietary fat intake is an ineffective method to mitigate the rise in obesity and improve public health.