TUCSON, ARIZONA. Low-fat diets have been widely promoted for lowering cholesterol levels, for reducing body weight, and for preventing certain types of cancer. At least one study, however, has found that although a reduction in cholesterol may reduce mortality from heart disease it may increase the incidence of fatal accidents, violent deaths, suicides, and depression. Researchers at the University of Arizona now believe that they may have found an explanation for this phenomenon. They point out that fat restriction and cholesterol-lowering drugs may change the concentrations of polyunsaturated fatty acids (PUFAs) in the tissues including nerve tissue (neurons). Fat-restricting diets usually lead to a relative increase in the intake of omega-6 PUFAs and a relative decrease in the intake of omega-3 fatty acids. This can have serious consequences inasmuch as the omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) found in fish oils, are crucial for the proper functioning of the nervous system. Several large-scale studies have found a clear association between low blood levels of EPA and DHA and an increased risk of depression, violence and suicide; a recent study in Japan found that DHA supplementation reduced aggression among healthy Japanese students.
Epidemiologic studies have found a clear correlation between a low intake of EPA and DHA and the prevalence of depression. In two studies of population groups in the USA the incidence of depression was found to be 3.7% and 2.9%. Average intake of EPA and DHA in the USA is estimated to be about 0.1 gram per day. In two Japanese studies, on the other hand, the incidence of depression was only 0.9% and 0% and the intake of EPA and DHA was 1.5 grams per day and 4.2 grams/day respectively. Other studies have shown that on-off dieting can produce a serious imbalance in the ratio of fatty acids and may lead to depression.
The researchers conclude that an extremely low-fat diet may be counter-productive and have deleterious psychological ramifications. They stress that dietary advice regarding cholesterol reduction, weight loss, and cancer prevention should emphasize the importance of an adequate intake of omega-3 fatty acids.
Bruinsma, Kristen A. and Taren, Douglas L. Dieting, essential fatty acid intake, and depression. Nutrition Reviews, Vol. 58, April 2000, pp. 98-108 [116 references]