I’m in my late 60’s and looking back at my school days I don’t remember more that 2 or 3 kids who we consider fat or obese. I always ate sack lunches until middle school and it was school lunches from then on. The lunches were made bu the school cooks and was pretty good. We always had milk, meats, veggies and breads of some type and in substantial amounts. I think the biggest difference was what we did when not eating, in classes, or at the house. We were always busy doing something outside, physical games or physical work. We would play football, baseball or basketball until the street lights came on or Mom called us in for supper. We were constantly on the move and in turn burning calories, I don’t think I could have ate enough to get fat back then.
I also look at the foods available at that time and cookies, candies, cakes and pie’s were a real treat but not common since most was home made. Very little of our meals came from a can or a package unless it was tomato sauce or basic broths. I don’t remember people eating any less back then but I do remember us being far more physical in our daily activities than what I see today.