A bit of a weird question, but why did Southern African kings frequently have beer bellies?

For example, [this portrait of Mzilikazi](https://en.m.wikipedia.org/wiki/Mzilikazi#/media/File%3AMzilikazi~detail.jpg) on Wikipedia and [this portrait of Mpande](https://en.m.wikipedia.org/wiki/Mpande#/media/File%3AKing-Mpande-1.gif) show the kings having large, protruding bellies. Wouldn't these kings have been highly physically active, given their military achievements?