[keltor]

Basically it's all about Calories and Americans have added 25% to their caloric intake since 1961 when it started increasing.

Its also not really magical, they didn't just add sugar, they added meat, sugar, grains and oil (replacing butter mostly) - all together it adds up to 720 kcal extra per day per capita.

Koreans eat about 1500 kcal less per day (they are also quite a bit smaller on average so it's not 1 ot 1 of course.) Japanese eat even less (like 200 kcal less) but are also even a bit smaller on average. Both countries happily eat terrible food just as much as Americans do these days, they just eat a lot less food in total.

There's an idea that American eat out more and that the calories at dining establishments about increased about 35%.

[nazgul17]

If it were walking what keeps Asians slim, you'd see more variation, imo. The small portions and generally healthier food are what keeps them slim. True that the Japanese eat fried chicken and cakes, but not as often as Americans, and not as much each time.

[washadjeffmad]

There's a certain positive status associated being "fat and happy" in the US.

Americans are also, on the whole, gigantic people. Tall, wide, huge frames and/or a lot of meat on the bone. Only some of that is accounted for by diet.

I think there's more to do in Japan locally, or at least more general social/physical freedom, which I attribute to low costs and high mobility. Nature in the US is generally privatized, far out of the way, or has limited access or parking. If you travel by walking in the US, middle class people think you're poor or your car has broken down. There's a bit of a stigma in some cases and places against not being sedentary and large (or, having to move and sweat for anyone).