Dietary Practices, Depression and Anxiety

The January 2010 American Journal of Psychiatry has two
articles pertaining to the relationship between dietary practices and
mental health.  One article presents the results of a study; the
other is an editorial.

href="http://ajp.psychiatryonline.org/cgi/content/abstract/ajp;167/3/305">Association
of Western and Traditional Diets With Depression and Anxiety in Women

Jacka et al.

Am J Psychiatry 2010; 167:305-311 (published online January 4, 2010;
doi: 10.1176/appi.ajp.2009.09060881) © 2010 American Psychiatric
Association

Objective: Key biological factors that influence the
development of depression are modified by diet. This study examined the
extent to which the high-prevalence mental disorders are related to
habitual diet in 1,046 women ages 20-93 years randomly selected from
the population.



Method: A diet quality score was derived from answers to a
food frequency questionnaire, and a factor analysis identified habitual
dietary patterns. The 12-item General Health Questionnaire (GHQ-12) was
used to measure psychological symptoms, and a structured clinical
interview was used to assess current depressive and anxiety disorders.



Results: After adjustments for age, socioeconomic status,
education, and health behaviors, a "traditional" dietary pattern
characterized by vegetables, fruit, meat, fish, and whole grains was
associated with lower odds for major depression or dysthymia and for
anxiety disorders. A "western" diet of processed or fried foods,
refined grains, sugary products, and beer was associated with a higher
GHQ-12 score. There was also an inverse association between diet
quality score and GHQ-12 score that was not confounded by age,
socioeconomic status, education, or other health behaviors.



Conclusions: These results demonstrate an association between
habitual diet quality and the high-prevalence mental disorders,
although reverse causality and confounding cannot be ruled out as
explanations. Further prospective studies are warranted.

Unfortunately, the full text is not openly accessible.  The
authors found that, after adjusting for potential confounding factors,
that "a 1.00-SD increase in the score for traditional dietary pattern
was associated with a 35% reduced odds for major depression or
dysthymia and a 32% reduced odds for anxiety disorders."  This is
a reasonably strong effect size. 



Naturally, studies such as these have plenty of problems that make it
difficult to draw firm conclusions.  One problem is that it is
tempting to believe the study, merely because if appears to confirm
what one might already suspect to be true. The authors point out that
reverse causality is a possibility.  That is, it is possible that
persons who already are anxious or depressed might tend to have worse
dietary practices.  This could lead to the same kind of
correlation, but the correlation would be reversed: the poor diet would
be caused by the emotional problems, as opposed to the poor diet
causing the emotional problems.  Also, even though they tried to
correct for confounding variables, it is possible that the statistics
corrections did not filter out the confounding effects.

href="http://ajp.psychiatryonline.org/cgi/content/full/167/3/244">Nutrition
and Psychiatry

Freeman

Am J Psychiatry 167 (3): 244

There is no abstract for editorials, so I will provide a brief
excerpt.  The purpose of the editorial is to put the Jacka study
in context, by citing some additional studies:

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).

These three studies tend to confirm the conclusions from the Jacka
study.  More fruit, nuts, legumes, fish, and monounsaturated fats
= good.  More processed foods and high-fat dairy products =
bad.  Metabolic syndrome = bad (although we already know
this). 



Although these studies are still not conclusive to the extent that I
would like, I feel comfortable saying that persons with anxiety and
depression are well-advised to try to improve their food selection
practices.