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Three quarters tolerate gluten when blinded
Who is really intolerant
Only about one percent of the population really has a gluten problem, celiac disease, and they vomit and have terrible diarrhea with the smallest bit of gluten. For the rest, some intolerance will be real, but most people who think they are intolerant aren't when tested. In the studies, someone slips them a biscuit or pasta to trick them.
Other explanations
Many probably have a more general irritable bowel syndrome and blame one protein out of the thousands in food. Cutting out bread can also make them feel better for other reasons: cheap bread causes glucose spikes and tiredness, and dropping it often means eating less processed food, or eating too much or too fast.
The vicious circle
Restrictive diets can start a vicious circle. A person gets nervous about new foods, sticks to a smaller and smaller group of them, and the microbes diminish, leaving much less flexibility to deal with any new food.
Why do blinded gluten tests change results?
In 2013, Jessica Biesiekierski and colleagues at Monash University ran a double-blind crossover trial in people with irritable bowel syndrome who believed gluten caused their symptoms. After everyone was put on a diet low in fermentable carbohydrates, adding gluten produced no specific worsening compared with placebo. Wheat contains fructans, carbohydrates that gut bacteria ferment into gas, which may explain symptoms often blamed on gluten.
Why does celiac disease react to tiny amounts?
Gluten contains gliadin peptides that resist digestion. The enzyme tissue transglutaminase modifies them in the gut wall, and they bind to immune molecules called HLA-DQ2 or HLA-DQ8, which triggers T cells to attack the lining of the small intestine. The finger-like villi that absorb nutrients flatten as a result. Nearly all people with celiac disease carry one of those two gene variants.
How does a narrow diet shrink gut diversity?
In a 2016 paper in Nature, Erica Sonnenburg and colleagues at Stanford fed mice a low-fiber diet and watched their gut species disappear. Across generations, many species were lost for good, and returning fiber to the diet did not bring them back. Only a reintroduction of the missing microbes restored the diversity.
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