> and as a result people had to resolve to eating more vegetables etc.

The "etc." is key here. "Cannibalism by necessity" was more common during World War 2 than most people realize. While it didn't hit the United States, we are still uncovering documentation of it happening on both sides of the war in Europe and Asia. You could make all sorts of dietary speculation about that as well.

But the reality is war kills the weak by numerous means and - surprise - you're left with a pretty healthy population.