And having grown up on the four food groups/home cooking/rare restaurant meals pattern, I can say this was NOT a low-carb diet, by any means. Yet, look at photos from 1958: you have to search for the merely chubby ones.
Of course, their bread was not drenched with weedkiller, and their food was not full of soybean fillers...
I was a chubby child on that type of diet - not nearly fat enough to need the chubby sized girls dresses, but compared to my normal cousins whose hand-me-downs I quickly outgrew sideways rather than lengthwise, I was definitely chubby, at least by the standards of the day, since this was considered to be chubby back then:
That particular ad has nipped in the waist a bit, and most likely slimmed down the arms and legs too - easy to do when it's a drawing, rather than a photo (no photoshop back then!), and they did that with all the chubby clothing ads back then, since they were trying to give the impression that their styles would make your chubby daughter look less chubby. Still, it's clear that they haven't reduced her to the typical thinness of most kids back then - the girl in that photo would look typical these days, maybe even a little more slender than most.
If I look at my photos from 1958 (age 5), I was definitely chubby.
The next year, I was extremely ill after a tonsillectomy, and took quite a long time to recover. During that extended illness, and unable to eat anywhere near as much as usual, I did lose some weight, so my school photo that year shows a somewhat thinned down version of me. My mother thought I was dangerously thin at the time, but in all honesty, I wasn't nearly as thin as my normal sized cousins.
A few months after recovering from that illness, full body photos show that I was back to my chubby self, and then some. Basically, I regained more than I lost at what should have been considered a shockingly fast rate, considering my age, and the fact that I was still a growing child. This all happened on a diet of the four food groups/home cooking. I honestly don't recall eating out even once in my life until at least the mid-60's - that's when we would eat out on very rare occasions, a few times a year.