There's a very interesting case study floating around the Internet. A woman of about 70 went on a low carb diet for weight loss and her hallucinations went away.

I can't seem to lay my hands on it right now, but from memory:

She'd been hearing voices since she was about 7 and had been dx'd with sz at 17. She'd been on multiple medications over the course of her life, and nothing had helped. She'd attempted suicide multiple times including several attempts in the months leading up to being put on the low carb diet. She'd had multiple hospitalizations.

After being instructed on the diet, she was scheduled for a follow-up appointment. During that appointment she mentioned in passing that on about day 8, her voices had stopped completely. They never came back.

In the case study the doctors talk about various reasons why the diet might have helped. They tentatively decide it was the elimination of gluten. That's why I tried my son on the gluten-free diet, but as I said it made no difference for him.

Obviously this is just one person, but I think it's sad that she went her whole life being tormented by voices, then a simple change in diet fixed it.