The Corpus Callosum

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.

Comments

  1. #1 Abel Pharmboy
    March 2, 2010

    Doc, did you see “Super Size Me” about Morgan Spurlock, the guy who tried to eat at McDonalds for every meal for a month? His fat consumption was through the roof and his cardiovascular endpoints were outrageous. But to the point of this post, he voiced many times how depressed he was. I’ve tried to search the internetz to see if he was ever evaluated with a HAM-D or other instrument at baseline and at the end of the 30 days, but it was clear in this n of 1 experiment that his mood suffered greatly.

  2. #2 G
    March 2, 2010

    “the correlation would be reversed: the poor diet would be caused by the emotional problems”

    For what it’s worth (probably not a lot!), that’s certainly how it works out for me. Stress factors of various kinds affect both my appetite and my ability to shop/cook in a healthy manner.

  3. #3 nutrprofe
    March 2, 2010

    The prospective study suggests that forward causation does exist. I believe there are other studies that show this, although newer studies using dietary factor analysis (Western factor versus Mediterranean factor) give stronger results than older studies looking just at saturated fat intake or some other isolated factor.

    However, the cross sectional data shows a stronger relationship, which suggests that reverse causation might contribute to the relationship.

  4. #4 Chad Peery
    March 2, 2010

    Both comments 1 and 2 are correct. Both indicate doorways to poor dietary habits and the corresponding decline of mood. Once the cycle is under way, it doesn’t much matter if it were the chicken or the egg.

  5. #5 Depression and Anxiety
    March 2, 2010

    Chad puts it perfectly, it is a typical ‘chicken or the egg’ situation. While there are a number of studies concluding an increase in depressive symptoms due to poor diet, those suffering from depression and anxiety often say that their poor diet originates from their emotional state. In any case it is evident that these diet habits can be a cause and effect of anxiety and depression, or at least increase the symptoms.

  6. #6 the alienist
    March 3, 2010

    Were any of these studies using an experimental design or were they all correlations? Not only could “reverse causation” be a conclusion, it is possible that there are other factors correlated with both depression/anxiety and diet (such as daily workload, for example) that account for the observed association in the absence of any direct causal relationship between diet and mental health.

    Still, it never hurts to advise people to eat well.

  7. #7 k8
    March 9, 2010

    I’ve been watching the controversy grow regarding the quality of school lunch, and I’m sure it’s way out of line in response to this particular study, but what is the quality of food at a typical inpatient behavioral health unit? I know the hospital I work for serves terrible, awful fatty and sugar laden food on a daily basis. Wouldn’t be a terrible thing to start investigating.

  8. #8 Shelley Strag
    July 4, 2010

    It’s interesting how anxiety and depression can relate to the quality of one’s diet. Add to the correlation between anxiety/depression and eating disorders and it becomes quite the tangled web!

  9. #9 Michel
    July 16, 2010

    Both comments 1 and 2 are correct. Both indicate doorways to poor dietary habits and the corresponding decline of mood. Once the cycle is under way, it doesn’t much matter if it were the chicken or the egg.

  10. #10 Dizi izle
    August 28, 2010

    For what it’s worth (probably not a lot!), that’s certainly how it works out for me. Stress factors of various kinds affect both my appetite and my ability to shop/cook in a healthy manner.

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