i really think it is guys being a bit too heavy for their structure but mostly due to carbing up and eating too much. also, the bigger guys have everything else that is bigger, so of course their guts will be bigger as well.
one of the reasons why i think this is bc sometimes, guys like dennis james, fux, ruhl, ronnie, nasser, dillett came onstage sometimes with very little distention compared to their last performance. perhaps they didnt carb up as much. the fact that they can control this form contest to contest could make this possible. i doubt they layed off the gh that much between shows to reduce the distention.