We have all heard the saying "you are what you eat" and I totally believe that is the case. Eating patterns and mood are directly related, for if you eat like crap you are going to feel like crap. 

Here is some evidence from Evolutionary Psychiatry 

Found two more studies measuring diet pattern and mood disorders!

The first one is Dietary pattern and depressive symptoms in middle age from the British Journal of Psychiatry in 2009 (free full text, go take a look!). This paper is part of the large Whitehall II epidemiological study, where some 10,000 people were screened at baseline (phase 1) for all sorts of demographic characteristics, stress levels, health, lifestyle factors, blood pressure, and some labwork. Every 2&1/2 years or so, the study subjects received a postal questionnaire to fill out (phases 2,4,6,8), and every 5 years a questionnaire and a clinical examination were done (phases 3,5,7). In this paper, the data was taken from 3486 White European participants with data on dietary patterns and all covariates at phase 5 and depression at phase 7. The 175 Black and 331 Asian participants were excluded due to "differences in eating patterns." (!!!)

Dietary "pattern" was determined by a Food Frequency Questionnaire based on the one used in the Nurses Health Study (but changed up to include British sorts of foods - like bangers and mash, or crisps, or yorkshire pudding). Here's a good write-up addressing the (actually rather rigorous, but still hopeless) validity of the FFQ used in the Nurses Health Study. 127 food items were rated according to how often they were consumed - "never or less than once per month" up to "six or more times per day" - the 127 items were divided into 37 groups, and dietary patterns were identified using "principal component analysis" of the 37 groups, and statisticians gleefully addressed the data with graphs and scree plots and tweaks and nudges until a score pops out about each person's diet, falling into "whole foods" or the "processed foods" patterns.

"Whole foods" were diets consisting of vegetables, fruits and fish.

"Processed foods" were diets consisting of "high consumption of sweetened desserts, chocolates, fried food, processed meat, pies, refined grains, high fat dairy products, and condiments."
 
The results are simple.

Patients with the highest intake of whole foods were less likely to be depressed (and this association wasn't affected much, actually, by adjusting for all the covariates, which is interesting - suggesting that the association with diet could be as important or more important than all those other covariates.). Patients with a high intake of processed food were much more likely to be depressed.

There is another interesting thing about this study. See, from just the above data, you don't know whether depressed people are too blue to do anything but sit around gorging on meat pies, sugar, and refined grains, or if the diet actually leads to the depression. The depression measures were repeated at phase 5 and phase 7, and when the 427 participants who were depressed at stage 5 were excluded, the data showed that the same people who had crappy diets but were not depressed (yet) at phase 5 were more likely to be depressed at phase 7. In addition, the researchers went back to the phase 3 data, and found no evidence that the dietary patterns in phase 5 were worse for the participants who were depressed at phase 3. These are clues that crappy diet precedes depressive symptoms, not the other way around.

All in all, a rather cool study, considering the limitations of epidemiology.

Read more compelling evidence here ...