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It appears to be a common strain of folk wisdom in Asia (or at least in Japan) that Asian people traditionally have had diets based on plants while Westerners have had diets based on meat, and therefore Asians have longer intestines that are suited to digesting plants. I thought this was an interesting claim, and I immediately had my doubts, but I am unable to find anything definitive that suggests this is true. Searching in English I can only find people speculating about it. Searching in Japanese there are numerous places saying that Japanese intestines are 2~3 meters longer than Westerners'.

There's a blog post here (in Japanese) that discusses it, but it's not making a claim either way.

This blog post cites two surgeons:

"You were right!" he said. After our dinner, he told me, he had emailed a gastroenterologist he knew in Tokyo. "My friend says Japanese intestines are definitely longer. Sometimes, when he's performing colonoscopies, he actually runs out of cable. He says he doubts such a thing ever happens in the United States."

I discounted this last testimony as ludicrous until a couple of years later, when my gallbladder became infected and had to be removed. After my operation, I asked my doctor, an American colorectal surgeon named Jeff Sternberg, the question I had now been asking for nearly 20 years. He surprised me in two ways: (1) by not dismissing the notion as ridiculous, and (2) by using the word "colonoscope" as a verb.

"I don't have data or anything," he said. "But it's kind of known in the field that when you colonoscope Asian woman, especially young Asian women, their colons are like, really freakin' long."

Is there any evidence to support or refute this claim that Asians have longer intestines? If not ethnicity, then can diet in general affect it, either evolutionary or through lifestyle?

I would be interested in seeing data for intestinal length of many different ethnicities, however the claim that they are making is about Asians vs. white people. (Note: the answer provide so far is indeed interesting but I have not accepted it because the actual claim is more specific).

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ssb
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  • Some clairifications: Is it enough to show that different ethnic groups have different average lengths, or do we have to show whether *Japanese* tend to be longer? What about confounding factors like weight and height? And do you mean diet over a person' lifetime or diet over evolutionary periods? – Oddthinking Nov 14 '13 at 13:54
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    The specific claim, to my understanding, is that Asian people in general (I'm assuming this refers to East Asian) and especially Japanese (since that's where this seems to be most prevalent) have longer intestines because they eat more plants. I'll try to find more information about whether they think this is evolutionary or not. I'll edit the question to reflect this too. – ssb Nov 14 '13 at 14:00
  • @Oddthinking - does weight and height significantly affect the intestine length in general? – user5341 Nov 15 '13 at 02:38
  • @DVK: My preliminary search found abstracts and hints that suggested it was correlated to height, correlated to weight but not height, was affected by race (but not in recent studies), was affected by race in Bolivia (?), and that race wasn't considered in many of the big studies - suggesting they didn't think it was a significant enough factor. I got mired in the mess and took a break. – Oddthinking Nov 15 '13 at 03:14
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    I've heard this myth in Japan as well, and it was typically not presented as caused by ethnicity, but by diet- especially because of the high amount of rice in the Japanese diet. – travisbartley Nov 19 '13 at 05:49
  • @trav1s that is one element of it that I'm not sure. As mentioned before, I think that it *is* an ethnic argument in the end based on adaptations to diet over the long term. Otherwise their claims wouldn't make sense in a time when people all over the world have really different diets within cultures. – ssb Nov 19 '13 at 06:13
  • An [avian study](http://jeb.biologists.org/content/206/11/1887.full.pdf+html) I found shows that gut/organ size can change *dramatically* when fed a high-fiber diet, even just over the course of a few weeks. I can't find similar studies for humans, but if there's a similar mechanism, this may not be an *ethnic* question, but based on an individual's diet over the course of their own life. The "different diets within a culture" argument would apply *now*, but probably not when this "common folk wisdom" first came into being. – Is Begot May 22 '14 at 13:28
  • There is a paper "An Analysis on the Length of the Large Intestine and Its Internal Diameter Amongst the Japanese" https://www.jstage.jst.go.jp/article/jcoloproctology1967/47/1/47_1_31/_article that measures length of colon for 232 Japanese. Now we need something to compare to. – DavePhD Dec 19 '16 at 14:07
  • Good info here: http://link.springer.com/article/10.1007%2Fs00276-002-0057-y Studies average colon length of men and woman and says "Conversely, Sadahiro et al., who measured the colon in Japanese subjects by rectal injection of barium, found that the colon was longer in women and explained this contradiction by racial differences" – DavePhD Dec 22 '16 at 22:00

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I couldn't find data on Japanese specifically but at least one study has looked at racial differences. This comparative study from 2011 Sigmoid colon morphology in the population groups of Durban, South Africa, with special reference to sigmoid volvulus

A total of 590 cadavers were examined (403 African, 91 Indian, and 96 White). Length and height of the sigmoid colon and mesocolon were significantly longer in Africans, and mesocolon root was significantly narrower in Africans.

What we don't know if this is acquired as a result of a diet high in roughage, or inherited.

The claim made about the Japanese colon is made by themselves, apparently as an explanation as to why they should not eat some Western foods.

Now since this study included Indian cadavers, and since Indians are considered South Asians, then it would appear that Africans have longer sigmoid colons than some South Asians.

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  • While this is indeed interesting, that doesn't answer the question at all. Your conclusion is Africans have longer sigmoid colons (this is only a quite short part of the large intestine) than some South East Asians. However the question was whether Asians (specifically Japanese, which are not South East Asians) have longer intestine (as in the whole intestine). – drat May 27 '14 at 10:28
  • It answers the last paragraph of the question. – HappySpoon May 27 '14 at 21:08
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    This race term in naive usage does not work for humans. There are no human races. As well unifying Indians with South Asians in biological sense is largely unsensical. They are in fact very closely related to Europeans und quite unrelated to Asians. Skincolour doesn't tell anything about ethnic group (thats the preferred term). – Raphael J.F. Berger Jun 02 '18 at 04:49