You can't claim this definitively though. Stutterers are usually mentally different to others. We have an unique mentality. Some people stutter more in restaurants, some people don't stutter on the phone, some do, etc. The restraint of fapping could give him more confidence because his mind tells him so. Surely there would be no evidence that eating rice could stop someone from stuttering, but if my unique and somewhat abnormal mentality told me that it'd help, then it probably would. Hope that makes sense.