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.
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.
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.