Physiques

[Inziladun]

The Men we see in the stories are mostly of Númenórean descent, or their distant relatives the Rohirrim. For the Númenóreans, perhaps the fact that it is said they had become the most like Elves of any Men had something to do with their tall, slim stature. The fact that Forlong was notable as "the Fat", seems to speak for the idea that obesity was a rarity for Gondor. Also, there could well be (and probably were) fighters in many of the great battles that were larger in girth than average. Since we as readers only see a tiny number of characters close-up though, the odds don't necessarily favour someone of "plus size" getting any notice.
We are told of some other races of Men that have a tendency to be smaller and stouter, though.

They are strong....countless companies of Men of a new sort that we have not met before. Not tall, but broad and grim, bearded like Dwarves, wielding great axes.

ROTK The Siege of Gondor