I'm not sure exactly whether the main difference between today's diet and that of 150 years ago was the proportion of carbs vs. fats or just the overall amount consumed. Obviously there was a big difference as far as the physical exertion put forth as well.
But it's hard not to notice the difference between the way Civil War soldiers looked --
-- and the way Civil War reenactors look:
Being lean not only makes you better-looking, it somehow makes you look more capable, and more serious as well. If either the Grays or Blues had seen opposing soldiers who looked like these reenactors, it would have undoubtedly boosted their confidence.
This may conflict with the spirit of the Fat Liberation Manifesto, but it doesn't conflict with basic human nature. There is something about a lean face that makes it seem more somber, and grim, and gritty -- as if the person behind that face is ready to wage war, as opposed to just play act at it.