I don't know a lot about that, but I have heard that sumo wrestlers tend to carry around as much subcutaneous fat as possible to give them mass. But that, due to their relatively healthy diet and constant exercise, they generally have low amounts of visceral fat. The suggestion being that they are much healthier than they may appear to our eyes. I haven't done any real digging into that, so all I really know is that they are shockingly athletic and agile for their size and power.
Regarding the Mongols... the newest, and only currently active Yokozuna... is a Mongol. Terunofuji. I don't know how long he'll be able to compete, as his knees are jacked up. But he's pretty dominant right now.