Something strange about Americans' eating habits

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I've heard that when you go to places like restaurants, the standard single serving of something like pasta is huge.
So, if you only hear that, you'd think they eat a lot,
but if you look at actual school lunches or military MREs, the portions aren't that large.
I'm curious if they just eat a lot but keep their lunches light,
or if they don't actually eat that much in reality.