That would be a good start. Caffeine binds to adenosine receptors, essentially blocking adenosine, which is a neurotransmitter that promotes relaxation. Whilst it’s doing this, dopamine surges in the brain. For a stutterer, that’s really bad and counterproductive. No to mention caffeine narrows blood vessels in your brain, reducing oxygen to your brain too. Not good! Plus it makes you feel more jittery, anxious and higher adrenaline (elevated heart rate). None of that is good for a stuttering brain. Ever since I’ve quit caffeine and refined sugary foods, my fluency has improved a lot.