Japan’s intestinal fortitude

Some of you may have heard the claim that Japanese intestines are longer, or in some other way, different from those of other people. This is of course just one part of the entire school of Nihonjinron (日本人論), or discussions on the uniqueness of the Japanese race/culture/nation/language. Unlike most of the nihongjinron pseudo-science (like Japanese use the opposite side of their brain to process language, etc.) this one sounds at least vaguely plausible. After all, there are all sorts of morpholigical differences between races; hair, skin, facial features, height, and so on. Could it be true?


Wikipedia has a neat little article on this topic, which for some reason is marked for possible deletion (revision maybe, but deletion seems pretty extreme.)

Several Japanese commentators (for example, then Agriculture Minister Tsutomu Hata, in 1987) have made the superficially plausible claim that Japanese intestines are qualitatively and quantitatively different from those of other humans and are, on average, significantly longer than those of non-Japanese people. This claim, which has been used to bolster the alleged uniqueness of the Japanese people, seems to have no basis in scientific fact. Though it is known that herbivorous mammals have longer intestines than carnivores, these differences are part of a long evolutionary process. Whatever differences there may be between the Japanese diet and that in Western countries, the time scale would be too short to allow for evolutionary changes. Although there are studies from non-human vertebrates concluding that an individual’s diet can have an effect on gut length,it is unclear whether this would apply to humans. The alleged fact of intestinal differences has also been used as an argument to ban imported beef into Japan.

I decided to check myself, through empirical measurement. I’ve seen all kinds of intestines and things for sale in Taipei’s night markets, but sadly there wasn’t a much of a range of human parts, and most of the samples were contaminated with delicious sauces.

I decided instead to see if anyone else had taken comparitive measurements of intestine size. Prowling scholar.google.com I didn’t find a whole lot, but what I did find is certainly interesting.

Anatomical study of the length of the human intestine

his anatomical study aimed to assess the length of the different intestinal segments, their variation and their correlation with sex, age, weight and height. Two hundred non-fixed adult cadavers (100 men, 100 women) who willingly gave their bodies for scientific purposes were studied. The post mortem average length of the whole intestine was 795.5-129 cm and was significantly longer in men and in young subjects. It was correlated with the subject’s weight but not height. Multivariate analysis demonstrated that the factor showing the strongest correlation with intestinal length was body weight.

For those who don’t know what colonic diverticulosis is (and I didn’t), it’s basically a hernia (or hole) in your colony. A primary cause of this disease is a fiber deficiency in one’s diet.

Comparison of etiology of right-sided diverticula in Japan with that of left-sided diverticula in the West

Background and aims. Colonic diverticula are located predominantly on the right-side in patients in Japan, in contrast to those in Europe and the United States. This study compared the etiology of right-sided diverticula in Japan with that of left-sided diverticula in the West.

Methods. A literature review was conducted from 1950 to 2001 using Medline and Index Medicus.

Results. Diverticula occur predominantly in the right-sided colon (over 70%) in Japanese patients, and even among Japanese who emigrate, in contrast with the diverticula in Western. Incidence (detection) rates of colon diverticula have rapidly increased in Japan since World War II with the increased dietary fiber intake. The increased detection rate over time is higher in urban areas than in rural areas, and it corresponds to the distribution of dietary fiber intake. Birth cohort analysis suggests that right-sided diverticula is affected more by environmental factors than other types. Furthermore, the significant relationship of right-sided diverticula with intraluminal pressure in Japan is similar to that of left-sided diverticula in the West, and the pathological feature of these diverticula are similar.

Conclusion. The etiology of right-sided diverticula in Japan (and perhaps also other Mongolian peoples) is very similar to that of left-sided diverticula in the West. The location may represent a difference in morphology of the large intestine between Mongolians (including Japanese), and Westerners, rather than environmental differences.

I wasn’t able to find a definitive study of intenstine length between ethnic groups, but surprisingly, this second study actually hints that there may be a genetic difference in large intestine shape. It seems to indicate that the rate of colon diverticula has increased in Japan along with their dietary fiber intake, which seems contrary to what I’d read. Doesn’t fiber protect you from this condition? Could it actually be true that Mongoloids, which would also include Koreans, Manchurians, Chinese, and of course Mongolians, in addition to the Japanese, actually have a digestive system adapted to a low fiber diet? Is there a grain of truth to this myth?

I don’t know much about medicine, and not a damn thing about diverticula, so if anyone out there DOES, please comment or email me.

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9 thoughts on “Japan’s intestinal fortitude”

  1. I’m currently living in Japan and I googled this question – which led me here – at the request of my girlfriend to check up on what was stated on one of the Japanese trivia shows. The panel of medical professionals on the show said, as a fact, that Japanese people have longer intestines (about 1-2 meters longer). Naturally, this isn’t any hard evidence for the statement, but it does show that Japan seems to stand behind this despite a lack of accessible proof. But don’t tell them that; many of the Japanese people I know are fairly nationalistic…

  2. http://jeb.biologists.org/cgi/content/abstract/206/11/1887

    There should be some reasons why suddenly after WW2 the rate of colon cancer was increased. I think the article above is just typo. Meat intake is increased but not fiber. Everywhere in the world has starving background. The US as the leading country is now suffering from oversized meals. It is very hard to get rid of excess amino acids from body caused by high meat consumption. I wonder if Japanese people also have started to have oversized meals after WW2.

  3. I heard that some German doctor who came to Japan about 200 years ago said that Japanese intestine is longer than Europeans.

  4. Roy wrote: “Some of you may have heard the claim that Japanese intestines are longer, or in some other way, different from those of other people…Could it be true? ”

    The Guardian today (among many similar reports):

    “The next time you order sushi in a Japanese restaurant, raise a glass of sake to the countless marine microbes that might be clinging to it. Bugs that live on the seaweed used to wrap sushi have given some of their genes to bacteria that live in the human gut, and in doing so, help them to digest the food. Scientists stumbled on the discovery after sequencing the genetic make-up of marine bacteria that live on Porphyra seaweed and searching DNA databases for matches. Eleven genes used by the bugs to break down carbohydrates in seaweed also showed up in bacteria isolated from the intestines of Japanese people, but were absent from the gut microbes of North Americans. Writing in the journal Nature, the scientists describe how a long tradition of a seaweed eating in Japan that dates back at least to the 8th century had caused their gut bacteria to adapt to the national diet.”

  5. Criticizing Japanese intellectual debate solely based on Nihonjinron(which is usually a norm among correspondents) is a bit unfair.It’s like arguing on American society solely based on argument made by the creationists.Me think.

    Anyway,all I can say is most of the Mongolian delicacy do not contain dietary fiber of anykind.Meaning my wife’s intestine is supposed to have much more resemblence with
    rancher in Nebraska or sheep herder of New Zealand.

  6. Concluding that all Japanese have this enzyme is strange to me. I mean, I thought the fact that Japanese have different types of ear wax, or different thicknesses of hair, was proof that the population is not homogenous. And if we are looking at gene transfer over hundreds of years, why are we examining Americans?

  7. Interesting article Mulboyne, and I must say that it sounds FAR more believable than the claim that the intestinal length of Japanese is different than other humans, for a variety of reasons. First of all, humans are not born with any gut flora – a newborn infant’s intestines are sterile. Second, the composition of gut flora is not determined by the human genome, but by environment and diet. Third, bacteria go through generations at a far, far faster rate than humans so it seems plausible that would, based on a different diet and environment, evolve rapidly enough to exhibit a significant difference from other populations.

    Since gut flora consist of many different species of bacteria that grow in response to different environmental stimuli, it further seems highly plausible that populations of humans with virtually the same genetic composition could develop highly divergent populations of gut flora. However, the nature of gut flora and their role in digestion was not known when the intestinal length story was popularized, which I think means that it can safely be said to remain in the realm of “nihonjinron” myth.

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