> The only country 1st world country not to have really obese people is Japan (~5% obese ~20% overweight). (~35% obsese ~70% overweight US) and I'd wager a large part of that is the fact that kids cook for themselves in school so they learn early what a reasonable meal is.
There might also be a genetic factor, why japanese are less obese or overweight, because the difference for diabetes patients between US and japan is a lot smaller.
There is no genetic factor because when Japanese people move to the States they are as obese as america's within 2 generation. I want to find the study but I think they end up being physically lighter because of other factors but are just as obese or overweight as americas[1]. The reasoning from the paper is that Japanese 2nd generation adopted western cultures eating habits
Being obese as a kid is almost causal for being obese later in life[1] as becoming obese screws up a lot of your bodies biology permenantly. You can of course change and become healthier but many lingering symptoms linger regardless of you losing weight. While still 70% obese adults were not obese as children 80% of obese children end up being obese.
Open to other ideas but school meals and peoples relationship with food is extremely important to maintaining weight in my experience.
[1] https://pubmed.ncbi.nlm.nih.gov/26696565/