Allergies that develop in the small intestine are not limited to fats. Allergens such as prawns, pollen, or gluten, for example, are not, in themselves, fat-bombs, and people who eat a fatty diet do not necessarily suffer from more allergies than others. Another theory about how allergies develop is this: the wall of our gut can become temporarily more porous, allowing food remnants to enter the tissue of the gut and the bloodstream. This is the theory under most scrutiny from researchers who are interested in gluten—a protein found in wheat and related grains.
Grains do not like us to eat them. What plants really want is to reproduce—and then along we come and eat their children. Instead of creating an emotional scene, plants respond by making their seeds slightly poisonous. That sounds much more drastic than it is—neither side is going to lose much sleep over a few guzzled wheat grains. The arrangement means humans and plants both survive well enough. But, the more danger a plant senses, the more poisonous it will make its seeds. Wheat, in particular, is such a worrier because it has only a very short window of opportunity for its seeds to grow and carry on the family line. With such a tight schedule, nothing must be allowed to go wrong. In insects, gluten has the effect of inhibiting an important digestive enzyme. A greedy grasshopper might be put off by a little stomachache after eating too much wheat, and that is to the benefit of both plant and animal.
In humans, gluten can pass into the cells of the gut in a partially undigested state. There, it can slacken the connections between individual cells. This allows wheat proteins to enter areas they have no business being in. That, in turn, raises the alarm in our immune system. One person in a hundred has a genetic intolerance to gluten (celiac disease), but a considerably higher proportion suffer from gluten sensitivity.
In patients with celiac disease, eating wheat can cause serious infections or damage to the villi of the gut wall; it can also damage the nervous system. Celiac disease can cause diarrhea and failure to thrive in children, who may show reduced growth or winter pallor. The tricky thing about celiac disease is that it can appear in more or less pronounced forms. Those with more subtle forms may live with the symptoms for years without realizing it. They may have the occasional stomachache, or their doctor might discover signs of anemia during routine blood tests. Currently, the most effective treatment is a lifelong gluten-free diet.
Gluten sensitivity, by contrast, is not a sentence to a life of gluten avoidance. Those with this condition can eat wheat without risking serious damage to their small intestine, but they should enjoy wheat products in moderation—a little bit like our friend the greedy grasshopper. Many people notice their sensitivity when they swear off gluten for a week or two and see an improvement in their general well-being. Suddenly, their digestive problems or flatulence clear up, or they have fewer headaches or less painful joints. Some people find that their powers of concentration improve, or that they are less plagued by tiredness or fatigue. Researchers began exploring gluten sensitivity in detail only recently. Currently, the diagnostic picture can be summarized as follows. Symptoms improve when a gluten-free diet is introduced, although tests for celiac disease show negative. The villi are not inflamed or damaged, but eating too much bread still appears to have an unpleasant effect on the immune system.
The gut can also become porous for a short time after a course of antibiotics, after a heavy bout of drinking alcohol, or as a result of stress. Sensitivity to gluten resulting from these temporary causes can sometimes look the same as the symptoms of true gluten intolerance. In such cases, it can be helpful to avoid gluten for a time. A thorough medical examination and the detection of certain molecules on the surface of the blood corpuscles are important for a definitive diagnosis. Alongside the familiar blood groups A, B, AB, and O, there are many other indicators for categorizing human blood, including what doctors call DQ markers. Those who do not belong to group DQ2 or DQ8 are extremely unlikely to have celiac disease.