We've covered ads for weight-gain products before. In them, it is very specifically mentioned just how frustrating it is to be skinny. Obviously, in the post-war/post-depression environment Americans being overly skinny became less and less of an issue.
"We Don't Want SKINNY on our team!" says the slightly thicker boy with the boldly-rendered crotch, while two midget boys below him declare "No Skinny Scare Crows for me!"
"Plus Weight helps you put on weight and improve your figure and looks by adding pounds and inches! 1500 calories when used as directed in each day's supply."
Ha, can you even imagine an ad like this running nowadays?
This ad for Plus Weight Company ran in Amazing Spider-Man #122, July 1973.