When I was in Japan someone offhandedly told me that too, and I thought it was strange. They said it as an explanation of why there aren't massively muscular Japanese men walking around everywhere like there supposedly are in the US (it's probably just because weight-lifting isn't as popular in Japan as in the west).
I would assume that a longer intestine would be better at absorbing nutrition from your food. So this explanation is actually the opposite of what I would expect.
It really seems like they've switched cause and effect around, they eat a less energy dense/harder to absorb diet, and their intestines get longer to compensate, also they don't buff up as much, because they have to work harder for their nutrition.
> it's probably just because weight-lifting isn't as popular in Japan as in the west
Don't discount the role of genetics. Some people are just naturally larger, others couldn't get large even if they tried. Although Japanese people would no doubt be bigger if there was more of a weightlifting culture, they'd still be slimmer than the average American.
And Japanese diets tend to have more soy which could lead to the explanation as to why Japanese men on average have more feminine characteristics. Studies have gone either way in suggesting this.
From left to right, American, North Korean, South Korean.
A empirical illustration of both the role of genetic factors (American vs. South Korean) and the role of non-genetic factors (South Korean vs. North Korean)
In the context of this discussion, it's really the NK vs. SK soldier that is interesting. The people of both N. & S. Korea are pretty close genetically, and presumably NK does not send their shrimps.
It would not surprise me if the South sent tall soldiers as well for such visible duty. While not directly relevant, it was slightly disorienting at the Forbidden City in Beijing when a group Chinese soldiers jogged by, every one of them well over six feet tall . . . absolute giants compared to the average people I saw around.
Various groups of human populations will have varying sorts of phenotypes, depending on the original conditions of their population.
The 'long Japanese colon' may be related to the fact that Japanese are also better at digesting seaweed than other populations: http://www.wired.com/2010/04/sushi-guts/
