Could ‘Modern’ Diet Raise Depression Risk?

Can an apple a day keep depression away?

Well, maybe, a new study suggests—at least if it's combined with other fruits, vegetables, beef, lamb, fish, and whole-grain foods.

The study was headed by Felice Jacka, Ph.D., a research fellow at the University of Melbourne in Australia, and her colleagues. The results were published in the March American Journal of Psychiatry.

The study included more than 1,000 randomly selected Australian women aged 23 to 93. Subjects were evaluated for current major depression with the Structured Clinical Interview for DSM-IV-TR and for psychological symptoms with the General Health Questionnaire–12.

Subjects also completed a dietary questionnaire that had been validated for evaluating dietary intake in the Australian population. The questionnaire asked, for example, “Over the last 12 months, on average, how often did you eat pizza?” and a subject had to check off one of 10 answers, from “never” up to “three or more times a day.” Similar questions were posed for 73 other foods and six alcoholic beverages.

The researchers then used a complex statistical procedure called “factor analysis” to analyze subjects' dietary habits. Simply put, all of the dietary variables recorded on the questionnaire were entered into a statistical package to see how they clumped together. This is a commonly used technique in nutrition research as it reveals how various foods tend to aggregate in people's diets.

Three common dietary patterns emerged from this analysis. One included vegetables, fruits, beef, lamb, fish, and whole-grain foods, or what the researchers called “a traditional [Australian] diet.” A second included hamburgers, processed meats, pizza, chips, white bread, sugar, and flavored milk drinks, or what the researchers called “a Western diet.” A third encompassed fruits, salads, fish, tofu, beans, nuts, and yogurt; the researchers named it “a modern diet.”

Finally the researchers looked to see whether the pursuit of a traditional diet, Western diet, or modern diet could be linked with a current major depression in their subjects,. Possibly confounding variables such as age, socioeconomic factors, education, physical activity, smoking, and alcohol consumption were considered.

An inverse relationship was found between a traditional diet and the odds of having a current major depression. Subjects who ate such a diet had a one-third lower risk of having major depression than did subjects who did not eat such a diet. Even though the study was of a cross-sectional nature, this finding suggested that eating a traditional Australian diet might prevent depression.

In contrast, no relationship was found between a Western diet and the odds of having current major depression.

However, the modern diet was linked with an increased risk of having major depression. This finding surprised the researchers. They had expected just the opposite—that a modern diet would be linked with a lowered risk of having a major depression. After all, the modern diet, like the traditional diet, included fish, and fish are known to contain omega-3 fatty acids, which have been linked with depression prevention.

There are several possible explanations for this unexpected finding, Jacka told Psychiatric News. Since the study was of a cross-sectional nature, it's possible that some of the subjects who were depressed switched to a modern diet hoping that it would attenuate their depression. Still another possibility is that some foods important for depression prevention besides fish were present in the traditional diet, yet not in the modern one—for example, “vegetables rather than salads, or good-quality red meat as opposed to tofu.”

They will now try to identify those particular foods in the traditional diet that may be capable of reducing the risk for depression. They will also be conducting a prospective study to determine whether eating a traditional diet can truly prevent depression.

The study was funded by the Australian National Health and Medical Research Council and Australian Rotary Health.

“Association of Western and Traditional Diets With Depression and Anxiety in Women” is posted at <http://ajp.psychiatryonline.org/cgi/content/full/167/3/305>.