I think it's a combination of factures, if they used a good probiotic and digestive enzymes to help breakdown all the food that would help as well as be conscious of their breathing when training and eating more meals with smaller portions, Coleman eats around 8000 calories+ a day in the off season but only eats something like 5-6 meals, then you get Cutler who will eat around the same amount of calories but eats 12 meals and doesn't have the gut. Look at Gunter, after working with Charles Glass, his waist has come down quite a bit and alot of that was learning how to breathe and keep your abs tight. Planks and side planks will also tighten up your abs. Another thing some people may not know is alot of guys don't even bother training abs or train them consistently, Ronnie's midsection was alot tighter at the last olympia because he trained abs a couple times a week and wore a weight belt more often.