Let's not forget that the gut is the second brain, which is where many neurotransmitters are created, vitamins/minerals are absorbed from food, etc. So in my opinion gut problems can most certainly lead to stuttering. I have been dealing with reflux for quite a while and it really messes with my sleep. I wake up feeling groggy and such and can tell upon waking how fluent I will be that day. I actually just had a surgery for the reflux and things have improved a bit but not completely. Also, worth noting that my stutter is very minor and a lot of days have no issues. Only days where I sleep bad.