The primary cause of midsection distension in most BB'rs is the diet...not GH, insulin, or IGF-1. The human digestive tract us not made to efficiently accomodate, process, or eliminate the quantity of food consumed by larger BB'rs and therefore, midsection distension is the inevitable result.
There can be great varaince in how diet might affect one's midsection...and metabolic rate will play a role as well, which is why we might see two BB'rs of equal size, but one with a much more distended midsection than the other. In terms of metabolic rate, those with slower metabolisms will not need to eat as much food in order to maintain an equal amount of mass and therefore, the possibility of suffering an equal degree of distension is reduced. Those with very fast metabolic rates must sometimes consume an extraordinary amount of food in order to maintain their mass, let alone grow further muscle tissue. Obviously, the more one eats, the more likely their chance of experiencing distension. However, despite these differences in metabolic rate, the average pro BB'r eats so much food that some degree of distension is almost impossible to avoid, even when all factors are lined up in their favor.
In regards to the diet aspect of distension, how the BBr's diet is constructed in terms of food type, will have a significant impact on the digestive system's ability to properly eliminate the food they eat. The average American has over 10 lbs of uneliminated digestive matter stuck to the sides of his digestive tract...some of which has been there for years. The famous actor John Wayne, due to his diet, had over 40 lbs of uneliminated waste stuck to his digestive tract, which was discovered during the autopsy.
Unfortunately, many BBr's follow a diet which is horrible when it comes to the elimination of digestive waste. I cannot even begin to tell you how many BB'rs diets I have seen which are almost entirely comprised of meat and fiberless starches, such as chicken, beef, fish, white rice, potatoes, and other refined carbs. Often, these diets contain little to no vegetables...little to no whole grains...and little to no fruit. This is a recipe for disaster in terms of dsigestive elimination and therefore, digestive health. Such a diet, especially when the BB'r chronically consumes between 4,500-6,000 cals per day, is gauranteed to result in the build-up of significant amounts of uneliminated digestive waste. Even when the BB'r follows a near perfect diet for fostering the removal of digestive waste, there wil still be a substantial amount of food in the digestive tract at all times, resulting in distension. Since such few BB'rs follow a diet tailored to the removal of digestive waste, how could we not see today's BB'rs suffering from distension?
The point is that in many BB'rs, the primary cause of midsection distension is NOT due to GH, Slin, or IGF-1. Of course, these drugs can exacerbate the problem, but in order for GH to cause significant distension by itself, very large doses would need to be used for years. Using 4-5 IU for 5-10 years is going to have a very minimal effect on gut size.
Sometimes, when BB'rs using these doses of GH notice that their guts have grown over they years, they are quick to point the finger at GH, but have they asked themselves if their diet now includes more calories compared to 10 years ago? If they have grown, especially considerably, it almost certainly does. In addition, just the act of growing larger muscles will lead to some degree of abdominal growth, as the body is not going to gain considerable amounts of muscle size over the entire body without affecting abdominal size. This is no different than when a BB'rs trains only his upper-body, yet his legs grow several inches over the years, despite doing zero leg workouts. The body likes balance and when the rest of the body starts getting to big, the few muscles which are not trained will grow automatically...not as much as the trained bodyparts, but still significantly in most cases. These are just a few of the factors which could lead to increased midsection growth over time, which have nothing to do with drug use.
Another factor responsible for some of the distension witnessed today is due to a weakening of the muscles which hold in the stomach. Even weight training can be partially responsible for distension, as the act of forcefully pressing outward against our inner abdominal wall when performing certain movments requiring core stabilization, can lead to a weakening of the inner abdominal wall respoinsible for holding our guts in. In the same way, chronic over-eating to the point of temporary distension will lead to permanent distenstion, as this also leads to a weakening of the muscles responsible for holding in our midsections. Repeated force against these supporting muscles causes them to weaken and stretch, allowing the gut to "fall" outward. Most large BB'rs suffer from both of these causes of distenson and don't even know it.
There are numerous factors which can play a role in midsection distension, but few of them are given any meaningful consideration by most BB'rs or even recognized as being a potentially serious contributer. I have isolated over 10 of these factors...and the larger a BB'r gets, the more likley he is to suffer from a increased number of them. Many large BB'rs suffer from them all. This is why it is possible for almost every large BB'r to drastically reduce the size of his waist, but it necessitates tackling the issue from every angle. I and others have had clients remove several inches from their waist from one prep to the next by addressing all of the relevant factors, sometimes taking the BB'r from a state of distension on contest day, to a waist which displays a concave appearance by the next contest.
Anyway, I could go on forever on this topic, so I'll stop now, but before I do, let it be known that I am NOT saying GH, IGF-1, and Slin cannot contribute to distension...they can, but they are often given a far larger share of the blame than they deserve, with many of the other contributers being ignored completely.