There are so many dietary regimes that claim to be really great for helping treat depression and other chronic health conditions! Some of these even greatly contradict one another, like vegetarianism/veganism vs. paleo/primal diets. There seems to be evidence that backs up the elimination of meat and an emphasis on grains, as well as evidence that backs up the elimination of grains and an emphasis on meat. With such varying opinions on what might be the healthiest diet, it is important for you start by merely having intention around the foods that you choose to eat. What are you consuming every day? Where does it come from? How was it processed? How does eating it make you feel (in the moment and long after the fact)? The most important thing to remember is that since each and every individual is different, with a personal constitution that is unlike anyone else's, what might be considered an "ideal" diet will vary from person to person.
That being said, there are some staples about diet worth mentioning. For example, it is widely accepted that highly refined foods made of simple carbohydrates and other sugars are considered to be toxic inside the body. Alcohol and caffeine (especially in large doses) have a similar effect. Processed foods that they include ingredients that are unrecognizable and unpronounceable should be avoided as well. And finally, meat products that are laden with hormones and antibiotics aren't good for the human body either; by eating them we ingest these synthetic drugs that were consumed by the animals as well.
Ultimately, ruling out the aforementioned ingredients will definitely help you feel happier and healthier. Once you've shifted to a more whole-foods approach to eating (with a lot of vegetables and fruits at the base) whether or not you eat grains, meat, both or neither is really up to how consuming this substances makes you feel. The greatest determiner of your health is how you feel and though this is a subjective experience, it can sometimes indicate a great deal more than any laboratory test a doctor could administer to you!
Good luck, and remember, bring intention to your eating habits! --