People are saying steroids, but that's not entirely true, anabolic steroids don't cause this, but human growth hormone and possibly exogenous insulin use are most likely the culprit. Bodybuilders are well aware of this phenomenon and although we still aren't 100% sure the exact mechanism, this started happening to bodybuilders who started taking insulin and HGH (in addition to anabolics) in the late 90s and early 00s. Either one, or both of these drugs cause the organs in the torso to grow (among other things) which causes what bodybuilders coined, Palumboism, named after the first guy to show up on stage with a noticable gut despite good conditioning (low body fat).
Yep, It is. The biggest danger being heart tissue hypertrophy, which has sadly taken the life of a few modern bodybuilders due to cardiac arrest (it can't pump blood effectively if the muscle walls get too thick). Don't take human growth hormone and/or exogenous insulin outside of medican supervision kids!