Nutrition and Psychiatry

Western medicine is struggling to keep up with the catastrophic effects of the western diet. Substantial durable dietary changes at the individual level are exceedingly difficult. Food intake habits are influenced by a complex array of factors. Eating is perhaps the quintessential biopsychosocial behavior, and mounting data suggest its central importance in the overall health of our patients. Obesity has been identified as a priority area by the National Institute of Mental Health, and studies have demonstrated that more healthful eating patterns are associated with better cardiovascular health (1, 2). We currently lack data from randomized, controlled trials to demonstrate the efficacy of healthful eating on psychiatric disorders. However, a growing body of epidemiologic evidence supports a relationship between nutrition and mental health. Manifestations of nutritional deficiencies include psychiatric symptoms, and single nutrients such as omega-3 fatty acids and folate have received attention in epidemiologic and treatment studies targeting mental health (3, 4). Now, new evidence is emerging regarding specific food intake patterns and risk of depression.

In this issue, Jacka et al. (5) present data regarding the association of dietary patterns with depression and anxiety. Jacka and colleagues conducted a cross-sectional study in Australia in which adult women were randomly selected. A comprehensive food frequency questionnaire was developed to reflect 12-month eating habits, and it was administered to each subject. The Structured Clinical Interview for DSM-IV-TR was utilized to assess psychiatric disorders, with particular focus on major depressive disorder, dysthymia, and anxiety disorders. The 12-item General Health Questionnaire (GHQ-12) was also used to quantify psychiatric symptoms. Covariates, such as socioeconomic status, education, physical activity, alcohol and tobacco use, and body mass index, were also recorded.

Diets were categorized into three types: traditional, western, and modern (Figure 1). A separate diet quality score was calculated on the basis of Australian national nutrition guidelines: "This scoring method assigns points for the consumption of desirable foods at the recommended levels; for example, a point is assigned for the consumption of at least two servings of fruit a day, at least five servings of vegetables per day, red meat consumption one to five times per week, using low-fat dairy products, and using high-fiber, whole-grain, rye, or multigrain breads. In addition, a maximum of two points was assigned for alcohol consumption at the recommended levels."

The authors found that the western diet was associated with higher GHQ-12 scores, although no relationship was found between GHQ-12 score and either the traditional or modern diet. A traditional diet was associated with a lower risk of a diagnosis of depression or anxiety, and a western diet was associated with a higher rate of depressive disorders. Higher diet quality scores were associated with lower GHQ-12 scores.

Two prospective cohort studies from Spain (6) and the United Kingdom (7) also provide information regarding the relationship between depression and patterns of nutritional intake. In the Spanish study (6), the Mediterranean dietary pattern was found to confer protection against the development of depression. Adherence to the Mediterranean diet was categorized into quartiles, with incremental increases in risk for depression associated with lower adherence. Particular inverse associations with incident depression were noted with higher consumption of fruit, nuts, and legumes, as well as a higher ratio of monounsaturated to saturated fatty acids. In the U.K. study, a dietary pattern containing higher amounts of processed foods was associated with a higher risk of subsequent development of depressive symptoms (7). Dietary patterns were assessed for "whole foods" (with fruit, vegetables, and fish characteristic of intake) and processed foods (largely represented by processed meat and bread products and high-fat dairy products). After adjustment for confounding variables, persons in the group with the highest intake of whole foods had the lowest rate of depressive symptoms on the Center for Epidemiologic Studies Depression scale. In addition, a study from France demonstrated an association between the metabolic syndrome and depression (8).

It is both compelling and daunting to consider that dietary intervention at an individual or population level could reduce rates of psychiatric disorders. There are exciting implications for clinical care, public health, and research.

It has been previously emphasized in the epidemiologic literature that "we do not eat nutrients, we eat foods…in certain patterns" (9). These patterns are influenced by cultural and environmental factors, including availability and accessibility of foods, ability to buy and prepare them, marketing, and educational efforts to foster healthy dietary intake (9).