As far as I know there has never been a correlation between food/diet and stuttering, and if there was it'd be pretty weird. It would be a bad idea to eat less just because it appears to have made you fluent for a day. And there really is no evidence that the fasting actually changed your fluency, it's very likely just correlation, not causation. The best advice I can give you is if you're not already in therapy, try to find a clinic somewhere nearby and see if you can meet with a speech therapist. A speech therapist will help you learn to use research-based strategies for making your speech more fluent.