You're right. I really never thought about it. But, when I was in high school and college almost everyone was thin (normal, not skin-and-bones). I recall that we almost never had snacks like Colas, packaged sweets and chips. A "Coke" was a treat that we got at the "service station" when on vacation or on a Sunday drive. (Sometimes we bought a small bag of salted peanuts and dropped some in the Coke bottle. Why did we do that?) If we had desert or a snack, it was homemade. We ate three pretty good meals a day and almost always ate at regular times with the whole family present. We were extremely active children, never occurred to us not to be active.
Some people these days don't believe those times ever existed. I remember one of the Sunday evening chores I had was Dad would give me a $1 to ride my bike to the corner store and pickup 2 candybars for everyone in the family. (we had 5 in the family--.10 per candybar) We got one while watching Mutual of Omaha's Wild Kingdom and the other while watching Disney! It was a treat for Sunday evenings. During the week we ate 3 meals a day, had an afterschool snack and played outside until the sun went down.
Cause the salt on the pnuts caused the coke to fizz. I used to do it too. Although as the mixture became more salty, the less fizz it produced.