The upper class (doctors, lawyers) consumed more food then the working class because they could afford it, yet there was no obesity.
It's not about calories.
It's not about sugar.
It's the PUFAs making us fatigued and sick.
PUFAs are the evolutionary signal for the coming winter and they reduce our metabolic rate which ultimately leads to sickness.
All mammals seek PUFAs when they want to go into hibernation and if you give them a PUFA free diet they will burn through their fat-stores within days.
Listen to this for the quote in the subject: https://youtu.be/QmNzV15Wads?list=PL_7Y5WbwJV_uFMcCRNFbEhmEfV9bLyw2m&t=2142
Then listen to the whole conversation or start at 24:40 to skip the first topic which is specifically about kids.
There are two great channels: "David Gornosksi Fan Favorites" and also "Danny Roddy".
These are the people they have lot's of conversations with:
Brad Marshall (Ex-Keto. Cook, Pigfarmer, Geneticist.) https://fireinabottle.net/
Dr. Ray Peat (Ph.D. in Biology) http://raypeat.com/
Georgie Dinkov http://haidut.me/
Not sure if it's ever mentioned, but did the means of calorie measurement change since then? 1939 was during the great depression and people, on average, were smaller in stature than today. Theoretically, that would mean they would have required less calories to exist/maintain the same muscle mass over time. I can understand folks back then being far more active, but even with a high activity level, calorie burn/day is only increased as a fraction of a much bigger total required to simply "exist"...the brain, heart, and other organs still burn the predominance of one's calories consumed.