The gut issue has a variety of reasons behind it, but the primary reasons involve insulin, and the fact that you can diet while taking in a lot more calories, (not to mention portion sizes), while taking GH, Thyroid, Huge amounts of AAS, etc.
Just taking low-doses of GH, will not create a gut, and even some people that are incredibly carb-tolerant, and get away with Insulin use, but combining the two, (which is mandatory in large doses as GH, and insulin are counter-reglatory hormones), will create a gut on anyone....given enough time.
M!