I was intrigued by this and did some very quick searching. Here is an article from 1948 which suggests that dietary differences are responsible for longer intes

I was intrigued by this and did some very quick searching. Here is an article from 1948 which suggests that dietary differences are responsible for longer intestines in Japanese and Russians: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1513781/pdf/annsurg01359-0189.pdf http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1513781/pdf/anns... Here is a review which mentions several articles in which investigators looked at intestinal length among westerners and Japanese, but the authors concluded that it was difficult to perform direct comparisons due to differences in measurement techniques. http://download.springer.com/static/pdf/803/art%253A10.1007%252Fs00384-002-0403-x.pdf?originUrl=http%3A%2F%2Flink.springer.com%2Farticle%2F10.1007%2Fs00384-002-0403-x&token2=exp=1440444635~acl=%2Fstatic%2Fpdf%2F803%2Fart%25253A10.1007%25252Fs00384-002-0403-x.pdf%3ForiginUrl%3Dhttp%253A%252F%252Flink.springer.com%252Farticle%252F10.1007%252Fs00384-002-0403-x*~hmac=8f6d7381fbf17c417e5efc6a8c15da477a37d739292b8537ed9dac4549b425fb http://download.springer.com/static/pdf/803/art%253A10.1007%...