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.