beyond substances that alter neurophysiology (alcohol, pharmaceuticals, illicit substances) I've never heard of any dietary substance that affects the frequency or severity of stuttering. But for shits and giggles I did a brief lit search for stuttering + diet. And Low and behold, I found a 1934 study entitled, "metabolic studies of stutterers" ... and they found no relationship between diet and stuttering. (although there was another article suggesting that stutterers are more susceptible to allergens. I'm skeptical of this -- it was a series of 8 case studies, so the data were probably biased.) All that to say--there's more than likely no relationship between stuttering and diet.