What causes an enlarged stomach in men?

Do U Mean...?: ...The organ that mixes food or are you referring to the abdomen? If the latter, a "big belly" is due to fat deposition within the abdominal cavity (the greater omentum) and the abdominal wall. As fat accumulates, the paired rectus ("6-pack") muscles split, creating the classic "beer belly". Of course, there are some serious diseases that can cause abdominal distention; so, if abrupt, see a dr.