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).