Hi tisha3, Welcome to Healing Well forum.
I really dont know of a diet that is going to help of set depression. There are quite a few people that believe that vitamins (SAM-e or St. John's Wart) for them are more effective than antidepressants. I am not one of those people. So I dont have any words of wisdom in that area either. Hopefully someone can come along and give you some suggestions soon. Good luck!!
You may want to make sure he gets a diet rich in Omega-3's like fish, salmon and such. I have heard that this can help but there are not any studies that prove it. Also he can take it in a supplement if he doesn't like fish. Lots of green vegetables are good too.
I am just a firm believer in antidepressants and haven't really concentrated on natural things to help sustain chemical balance. But I would give these a try or do some research on it. Sorry I cant be of more help.