Now I'll review the other major dietary observational studies regarding depressive disorders.
Dietary patterns and depressive symptoms among Japanese men and women: 521 men and women filled out dietary surveys and mental health questionnaires. Once again three dietary patterns were identified - and those who ate fruits, vegetables, mushrooms, and soy (called the "healthy Japanese diet" group) were less depressed.
Vegetarian diets are associated with healthy mood states: a cross-sectional study in Seventh Day Adventist adults: 60 vegan Seventh Day Adventists were compared with 78 omnivorous Seventh Day Adventists. The vegans reported a much higher intake of flax oil (an omega 3 fatty acid, ALA) and linoleic acid (omega 6 fatty acid). The plasma and tissue if the participants were not measured for their fat content, but vegans generally have a red blood cell phospholipid ratio (omega 6 to omega 3) of 18.6 compared to 9.9 in omnivores. Also, the vegans were generally happier! (see table).
Association of the Mediterranean dietary pattern with the incidence of depression: 10,094 Spanish men were followed for an average of 4.4 years. Participants were each given a Mediterranean Diet Compliance score based on positive points for consuming vegetables, fruit and nuts, cereal, legumes, and fish, a good monounsaturated- to saturated-fatty-acids ratio, and moderate alcohol consumption. Participants got a negative score for "meat" and whole-fat dairy. Over those 4.4 years, 480 new cases of depression were identified (as in the other two studies, anyone with depression or taking an antidepressant medication at the beginning was excluded from the study.) In general, the higher the diet compliance score, the less depressed the participants were, with intake of monounsaturated fats, nuts, fruits, and legumes seeming to be especially protective.
Anxiety and depression in adult patients with celiac disease on a gluten-free diet:
Germans (primarily women) with Celiac Disease on a gluten-free diet were compared with a group of Germans with inflammatory bowel disease (Crohn's or Ulcerative Colitis) and a group of normal controls. Women with IBD and celiac disease were both more anxious than the controls. Men seemed to be serene no matter what. Adherence to the gluten-free diet didn't seem to matter much with regards to level of anxiety. In a related study, anxiety improved in patients with celiac disease in a year on a gluten-free diet, but not depression.
In summary - we get the usual mish-mash with the observational studies. Vegan Seventh Day Adventists are happy folks. German women with celiac disease tend to be anxious, and the Mediterranean Diet appears to be protective against depression, at least in Spanish men! The most surprising finding for the researchers in any of the studies appeared to be the happy vegans, given the strong evidence in prospective trials for an antidepressant effect from fish oils. While limiting the study to Seventh Day Adventists was meant to be a control, it may mean that you can't generalize the results to the rest of the vegans and omnivores in the world. I know very little about Seventh Day Adventists, but maybe eating vegan every day as a religious practice is self-affirming and has an antidepressant effect of its own, for example. Clearly, though, the omega 6 to omega 3 ratio is not the end all, be all factor in the brain. Stuff to keep in mind!