I think if you search a bit you'll find that is a stereotype and not really true.
Sure, they might be less obese than we are, but "very rare" is prolly exaggerated a bit.
I don't think it's that much of an exaggeration
My town is 22% Asian. Other local North Bergen County, NJ, are way over 22 %.
Of the 5 houses that abut mine, two are Asian, one Indian, and two caucasion. Riding up my block, many other houses are owned by Asians and Indians.
One house next to mine is a rental, and since the owner is Asian, she only rents to Asian families. They frequently have other Asian families over their house for a "kid's playtime".
Never saw one of the mothers overweight.
The Asian father next door must do a lot of business travel, because he's out of town frequently.
To see this very slim Asian mother out there with a shovel this past winter looking at 24-36" of driveway snow was sad, but since I still shovel at 68 years old, I'm sorry to say I couldn't help her.
At our local stores, I haven't taken any scientific poll, but if memory serves me, not many overweight Asians.