Here's a couple.
Side Effects of Overproducing Insulin
Over production of insulin can aggravate or trigger other problems including infertility, weight gain, bloating, poor lipid profiles, hormonal imbalances, cosmetic problems (hair loss, hirsutism, skin tags, acanthosis nigricans), and contribute to more serious health risks like high blood pressure, heart problems, and an increased risk of developing diabetes, and gestational diabetes during pregnancy.
A pancreas that continually over produces insulin may also, over time, wear out, in which case a patient usually will need to take insulin.
http://www.isletsofhope.com/metabolic/insulin_resistance_1.html#side
http://web.indstate.edu/thcme/mwking/diabetes.html
Yes, I know and understand all about insulin resistance, insulin spikes, diabetes and the like. That certainly doesn't amount to a 'proof' that it is the only thing responsible for the large guts of professional bodybuilders.
One of the major side effects of taking the vast amounts of HGH that bodybuilders do is the overproduction of insulin. Abusive use of GH can cause diabetes. So even if the guts are exclusively the product of insulin that still doesn't rule out the root cause being GH. Although I don't believe that insulin is the soul culprit as autopsies on those who used excessive amounts of GH have shown enlarged hearts, 30lb livers and intestinal growth.
Also, whilst I understand that what is forcing the stomach out in such an protruding manner could partly be fat storage around the organs ..there is also, uncoiled, something like half a mile of intestines behind it. When someone is at 4-6% bodyfat with clearly defined abs yet still has a giant belly, then it seems a little absurd to say that there is no possibility this huge mass of tissue hasn't grown when we know that the whole point of GH is to promote growth and the spill over effect it that it grows
everything..
Gh and insulin are not mutually exclusive ..GH causes uncontrollable insulin spikes. Like I said, when you factor in the forced feeding this will exacerbate the problem but the stomachs have all coincided with the emergence of HGH..We know that it enlarges all muscles, organs , tissues and even bones when used..so why deny that it enlarges the organs and intestines behind the gut?
Personally, I think my answer is much more sound.. especially as the GH causes all the deleterious effects that you cite and that it would explain why even at ultra-low, dangerous levels of bodyfat they still have stomachs that are painfully straining and being aggressively forced out, without any ability to control it.