Celiac disease, a kind of gluten intolerance, is very underdiagnosed. There was an epidemiological study (Fasano et al, Arch. Internal Medicine 2003 Feb 10; 286-92, "Prevalence of celiac disease ...") which found a rate of celiac disease of 1/111 among adults. It had been diagnosed at a rate of 1/4500 in the US.

People with celiac disease sometimes can't absorb their food, especially fat, and they get underweight, and they may even starve to death. If they have these symptoms they're likely to get diagnosed. But what Fasano's study found was that most celiacs don't fit this picture. More of them were overweight than underweight. Many celiacs are asymptomatic. Many do not have intestinal symptoms, like stomach pain or diarrhea.

So they suffer for years from problems like vaguely feeling bad, joint pain, osteoporosis. And GI tract cancer. Colon cancer is common. I wonder how many people who get colon cancer are gluten intolerant?

A lot of people who have delayed food allergies likely have celiac disease; doctors don't think to test, and many celiacs don't have the typical intestinal symptoms, but other unsolved medical problems. CD causes intestinal permeability which causes allergies to foods besides gluten.

Celiac disease can be diagnosed by a blood test or a small-intestine biopsy.

Enterolab sells a gluten sensitivity test that's more sensitive than blood tests or a biopsy. Their test might show if people are in the very early stages of celiac disease, or may later develop it.