There is more to wheat than gluten. Wheat also contains a combination of complex carbohydrates, and the Australian team wondered if these could be responsible for the problems. Gibson and his colleagues devised a different study: they recruited a group of thirty-seven volunteers who seemed unable to digest gluten properly. This time, the researchers attempted to rule out the carbohydrates and confirm gluten as the culprit. Gibson put all the volunteers on a diet that was gluten-free and also free of a group of carbohydrates that he and his colleagues called FODMAPs, an acronym for a series of words that few people will ever remember: fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. Not all carbohydrates are considered FODMAPs, but many types of foods contain them, including foods that are high in fructose, like honey, apples, mangoes, and watermelon; dairy products, like milk and ice cream; and fructans, such as garlic and onions.
Most people have no trouble digesting FODMAPs, but these carbohydrates are osmotic, which means that they pull water into the intestinal tract. That can cause abdominal pain, bloating, and diarrhea. When the carbohydrates enter the small intestine undigested, they move on to the colon, where bacteria begin to break them down. That process causes fermentation, and one product of fermentation is gas. In Gibson’s new study, when the subjects were placed on a diet free of both gluten and FODMAPs, their gastrointestinal symptoms abated. After two weeks, all of the participants reported that they felt better. Some subjects were then secretly given food that contained gluten; the symptoms did not recur. The study provided evidence that the 2011 study was wrong—or, at least, incomplete. The cause of the symptoms seemed to be FODMAPs, not gluten; no biological markers were found in the blood, feces, or urine to suggest that gluten caused any unusual metabolic response.
–Michael Specter, in The New Yorker, on the “gluten-free” craze and the science behind it.
Photo: reid-bee, Flickr