Diet Rich in Processed Food Linked to Increased Risk for Depression

Pauline Anderson

November 05, 2009

November 5, 2009 — Patients who consume a diet rich in high-fat dairy products and fried, refined, and sugary foods are at increased risk of developing depression, whereas those whose diet is rich in fish, fruit, and vegetables are at lower risk of developing depression, a new study shows.

Although other research has looked at the relationship between single nutrients and depression, this is the first study to investigate the effect of dietary patterns on depression.

The results suggest that diet should be considered a potential target for the prevention of depressive disorders, said the study's lead author, Tasnime N. Akbaraly, PhD, who completed the study while at the Department of Epidemiology and Public Health, University College, London, United Kingdom.

"The study can be an argument to help convince patients who have unhealthy eating behaviors that consuming a healthy diet not only controls excess weight but also may lower the risk of depression," Dr. Akbaraly added.

The study was published in the November issue of the British Journal of Psychiatry.

2 Dietary Patterns

Part of the Whitehall II, a population-based study of London-based civil servants aged 35 to 55 years, the analysis included 3486 patients who completed the Food Frequency Questionnaire.

Participants were asked how often, on a 9-point scale ranging from never to 6 or more times per day, they consumed a list of 127 foods in the previous year. The food list was "anglicized" and included foods common to the United Kingdom — fish and chips, for example, said Dr. Akbaraly.

Along with her colleagues, Dr. Akbaraly grouped the foods into 37 predefined food groups and eventually created 2 dietary patterns — a "whole" food pattern that included a high intake of vegetables, fruits, and fish, and a "processed" food pattern that included a high consumption of desserts, fried foods, processed meat, refined grains, and high-fat dairy products.

The latter diet is similar to the "Western" diet, said Dr. Akbaraly who is now at the Institut National de la Sante et de la Recherche Medicale, in Montpellier, France.

Novel Finding

Five years later, the participants completed the Center for Epidemiologic Studies–Depression, a 20-item self-report of depressive symptoms. Using a 4-point scale, participants were asked to score the frequency of their depressive symptoms during the previous week.

The study found that participants with a high intake of processed foods had higher odds of depression compared with those with the lowest intake (odds ratio, 1.58; 95% confidence interval, 1.11 – 2.23).

"This finding was observed after taking into account the potential confounding factors such as age, socioeconomic status, education, marital status, total energy intake, other health behaviors, and other health status, making the associations very robust," said Dr Akbaraly.

She added that this is a novel finding. "There are no studies showing the deleterious effect of food pattern on depressive symptoms."

As for participants who fell into the whole food dietary pattern, the study found they were less likely to report depression (odds ratio, 0.64; 95% confidence interval, 0.49 – 0.93) after adjusting for potential confounders.

Potential Mechanisms

There are several possible mechanisms that might explain the association between a processed food diet and depression, said Dr. Akbaraly. There is some evidence of a correlation between sugar consumption and the rate of depression.

In addition, the Western diet has been associated with higher risk of coronary heart disease and inflammation, both of which have been reported to be involved in the pathogenesis of depression.

"Many processes such as oxidative stress processes, or insulin resistance processes, could be involved," said Dr. Akbaraly, adding that further research is needed to determine exactly how refined foods might affect risk for depression.

As for how a "whole" food diet might protect against depression, such a diet includes fruits and vegetables that are rich in antioxidants — nutrients that have been shown to reduce risk for depression.

In addition, the diet includes many foods including cruciferous vegetables, leafy vegetables, and other vegetables and dried legumes that are a rich source of folate. Previous research has shown that low levels of folate may affect levels of neurotransmitters that may be involved in depression. This diet also includes lots of fish, a source of polyunsaturated fatty acids that might also reduce the incidence of depression.

Target for Depression Prevention?

However, according to Dr. Akbaraly, the benefits of the whole food diet do not lie in individual nutrients. "In my opinion, the protective effect of diet on depression comes from a cumulative and synergistic effect of different nutrients from different sources of foods, rather than the effect of one isolated nutrient. If that's the case, it's important to assess the impact of the overall diet on health outcome, as people don't eat isolated nutrients."

The study results could result in diet becoming a potential public health target for depression prevention, said Dr. Akbaraly.

To verify that dietary patterns affected depression, rather than the other way around, the authors undertook a series of sensitivity analyses. They found no significant association between previous reports of depression and dietary patterns assessed 6 years later, suggesting that depression did not predict dietary behavior.

In addition, the association between dietary patterns and depressive symptoms remained significant after excluding participants with prior depression.

Although a healthy diet may be only 1 component of a healthy lifestyle, the results of the study did not change significantly after adjusting for lifestyle factors such as physical activity, smoking, total energy intake, and body mass index.

Are Results Generalizable?

Asked by Medscape Psychiatry to comment on the study, Michelle B Riba, MD, a past president of the American Psychiatric Association and associate chair and professor of psychiatry, University of Michigan, Ann Arbor, said the study adds important information to the depression literature.

"This is a good step, and the authors should be commended," she said, adding that a lot of patients want to learn what lifestyle habits might help prevent depression.

However, she added, it is a single study and it has limitations. The study sample — middle-aged, white office workers who self-reported their dietary intake — is somewhat "skewed," she said.

"The investigators did have blacks and Asians in the survey group but took them out due to differences in eating patterns," said Dr. Riba. "They were studied but not included in the results, which is a limitation to the usefulness of the study to other groups of people."

The authors have disclosed no relevant financial relationships.

Br J Psychiatry. 2009;195:408–413. Abstract

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