Food Blues: Diet and Depression

Abstract & Commentary

By Russell H. Greenfield, MD, Editor

Synopsis: Taking data from a large cohort being followed prospectively, the authors of this trial found that a dietary pattern disturbingly similar to our "Western-style" way of eating is significantly associated with a greater risk for self-reported depression at 5 years of follow-up when compared to an eating pattern that more closely mimics the Mediterranean- or Asian-style diet.

Source: Akbaraly TN, et al. Dietary pattern and depressive symptoms in middle age. Br J Psychiatry 2009;195:408-413.

While a number of research trials have examined associations between specific nutrient intake profiles and incidence of depression, few have explored any association between mood and dietary patterns. The authors of this study used data collected from Food Frequency Questionnaires (FFQs) and factor analysis to assess the presence or absence of correlation between incident self-reported depression and dietary pattern.

Information was gleaned from participants in The Whitehall II longitudinal prospective cohort study, specifically from people age 35-55 years working in any of 20 civil service departments in London (n = 3,486 participants; 26.2% women). Baseline screening (phase 1) for Whitehall II took place from 1985 to 1988 and included clinical examinations and a self-administered questionnaire containing sections on demographic characteristics, health, lifestyle factors, work characteristics, social support, and life events. Subsequent data collection occurred at specified times and alternated between that gathered from mailed-in questionnaires alone (phases 2 [1989-1990], 4 [1995-1996], 6 [2001], and 8 [2006]) and that collected from the questionnaire combined with clinical examination (phases 3 [1991-1993], 5 [1997-1999], and 7 [2002-2004]).

A machine-readable FFQ (similar to the one used in the Nurses' Health Study) with a food list of 127 items was sent to participants. Based on the nutrient profile and culinary use of food items, the 127 items were grouped into 37 predefined food groups, and dietary patterns were identified. Two unique dietary patterns were identified: "whole food" (emphasizing intake of vegetables, fruits, and fish) and "processed food" (emphasis on sweetened desserts, fried food, processed meat, refined grains, and high-fat dairy products). Approximately 5 years later, self-reported depression was determined using the Center for Epidemiologic Studies-Depression (CES-D) scale.

Analyses were limited to those participants with available data on dietary pattern and all covariates at phase 5 and depression at phase 7. Fascinatingly, Black and Asian subjects were excluded from this analysis due to "differences in eating patterns."

By the time of phase 7, a total of 416 participants were categorized as having depression based on CES-D (score > 15). Subjects who largely followed the "whole food" dietary pattern were less likely to report CES-D depression (odds ratio [OR], 0.64; 95% confidence interval [CI], 0.49-0.83) after adjusting for age, gender, and energy intake. This association was altered only minimally after adjustment for all possible covariates (OR, 0.74; 95% CI, 0.56-0.99). Participants who followed the "processed food" dietary pattern, however, were at greater risk for depression compared with those with a lower intake of the same types of food (OR, 1.58; 95% CI, 1.11-2.23). When additional sensitivity analyses were performed on subsamples with data on BMI and dyslipidemia, similar results were found.

The authors summarize their findings by stating that with respect to incident depression there appears to be a protective effect from an overall diet rich in fruits and vegetables and fish, whereas a diet rich in processed meats, chocolates, sweetened desserts, fried food, refined cereals, and high-fat dairy products seems to increase risk of depression at 5 years of follow-up.

Commentary

Most of us have some sense that the findings of this study ring true, even on a personal level. On an objective level, previous studies have strongly suggested that following a Mediterranean-style diet can offer long-term health benefits not limited to the cardiovascular system, but also on cognition and mood. The regular ingestion of omega-3 fatty acids, commonly found in cold water fish, has been tied to improved mood states, and some studies have explored the impact of B vitamins on depression. The question that sticks with us, though, is, "Does the dietary pattern contribute to incident depression, or does a depressed person just eat less healthily?" The authors of the present study were well aware of this issue and expended great energy in attempts to evaluate reverse causation through a variety of analyses, the results of which all pointed in the direction of diet's impact on mood having primacy.

The results are compelling for many reasons, not the least of which is the way the researchers controlled for a wide variety of potential confounding factors. It's also easy to posit that the beneficial impact of the "whole food" dietary pattern might be related to a high antioxidant or anti-inflammatory compound intake, as opposed to the pro-inflammatory nature and high glycemic index of many of the foods that might be regularly ingested on the "processed food" diet.

Questions still linger, however, about whether behaviors often associated with following a healthy diet (regular exercise, for example) might have as much or more to do with the results than simply the dietary pattern followed. Another challenge is the lack of generalizability of the findings due to the fact that the conclusions can only be comfortably applied to a largely white, middle-age population of civil service workers in the United Kingdom. These limitations, while noteworthy, are minor when compared to the dietary mandate that can be drawn from the strength of the results.

Many people feel there is little they can do to help prevent or treat mild-to-moderate depression on their own. How refreshing as a physician to be able to share with our patients that modifying their diets, as part of an overall wellness plan, may not only keep their bodies healthy, but their minds at peace, too.