Many people have an intuitive sense that a good diet is a foundation stone of good mental health. We don’t disagree, although the evidence for dietary manipulation’s effectiveness is not overwhelming.
There are a couple of things that we have noticed over the years about food and its effect on mood that might be useful tips.
For one thing, simple carbohydrates (white flour and sugar are the best examples) do have powerful effects on mood that are a bit reminiscent of some drugs of abuse. They have an immediate effect of reducing anxiety. This has recently been demonstrated in studies, but has been long known to most of us who have struggled to avoid weight gain when stressed. But they have less obvious but pretty powerful long term effects of increasing anxiety and mood instability. In many ways they are a bit like “downers”… they have an immediate effect of reducing anxiety but over time the brain’s reaction to frequent use actually increases baseline anxiety… which in turn makes eating them seem even more necessary… a vicious circle.
How to break that circle? Honestly some form of abstinence with its associated withdrawal may be necessary… an elimination diet of some kind. This can be a “paleo” diet, or an “Atkins” diet or a South Beach Diet. What we notice is that after the first week maintaining the diet becomes effort free. So line up your support for a hard first week but then you can expect things to be a lot easier.
The second thing that we have noticed is that ketosis (which is the state your body will get into if you eat no or very 
little carbohydrates – as in the Atkins diet, or if you are starving) is sometimes associated with a mild hypomania (or energized state). This makes some sense if you think of all of those mystics off in caves by themselves having mystic experiences over the centuries.
There are some real risks to this state from a health standpoint (recent data on the Atkins shows it can increase cardiac events even as it causes weight loss which should protect the heart). And living as a mystic may not be all that great if you want a stable life, either.
Here are some books that may help you plan a change in diet.