Celiac disease is an autoimmune disorder that affects less than 1% of the population of the United States (PDF). The ingestion of gluten, a protein found in grains like wheat, rye, and barley, gives rise to antibodies that attack the small intestine. At first, the symptoms are annoying: stomachaches, gas, and diarrhea. Over time, they can grow to be debilitating. The autoimmune assault corrodes the small intestine's ability to absorb nutrients, which can prompt anemia, chronic fatigue, and weight loss. There is one treatment for celiac disease: strict, lifelong adherence to a diet that's devoid of gluten.

Yet despite the rarity of celiac disease, a growing number of people in the Western world are adopting a gluten-free lifestyle. In Australia, for example, for every person who's diagnosed with celiac disease, there are 20 others eating gluten-free food. It's likely that the numbers are similar in the U.S., if not more extreme.

Many of the people who pursue a gluten-free diet out of choice believe themselves to be gluten-sensitive, a far less serious condition in which limited symptoms of celiac disease manifests without any damage to the small intestine. According to the National Foundation for Celiac Awareness, as many as 18 million Americans may have non-celiac gluten sensitivity (NCGS). Since the condition has only been recently described and is poorly understood, it's currently diagnosed via a process of exclusion. If a patient's test for celiac disease comes back negative, but symptoms improve on a gluten-free diet, then he or she is diagnosed with NCGS.

Instead of receiving a proper diagnosis, however, many people are self-diagnosing as gluten-sensitive and eating gluten-free by choice. Noticing this trend, Jessica Biesiekierski, a gastroenterologist at Monash University and a leading researcher into the effects of gluten, sought adults who believed they had NCGS to participate in a survey and a clinical trial. She recruited participants in metropolitan Melbourne, Australia by distributing fliers through websites and local clinic rooms and taking out advertisements in a local newspaper. 248 people responded, 147 completed an in-depth survey designed to assess the nature of their sensitivity, and forty were recruited into the clinical trial.

First, the survey results: The average age of the respondents was 43.5 years and 130 (88%) were women. These numbers are likely a result of sampling bias, but could reflect the demographics of those who engage in a gluten-free diet by choice. For 63% of respondents, the gluten-free diet was either self-initiated or started at the recommendation of an alternative health professional. Inadequate investigation of celiac disease was common (62%), particularly by individuals who self-diagnosed their sensitivity or sought guidance from an alternative health professional. This is concerning, because, as explained earlier, celiac disease can severely damage the small intestine, and if not properly treated, could lead to other deleterious health conditions. Interestingly, just 28% of survey respondents actually fulfilled the diagnosis for NCGS. Moreover, 24% of respondents had uncontrolled symptoms despite restricting their gluten intake, and 27% weren't even following a gluten-free diet.

For the clinical trial, in which 37 subjects self-diagnosed with NCGS participated, Biesiekierski tested an alternative explanation for gluten sensitivity. Most gluten-containing products also have fermentable, poorly absorbed, short-chain carbohydrates, collectively known as FODMAPs, which are known to cause gastrointestinal problems. Biesiekierski wanted to know if FODMAPs were actually the villains behind subjects' gastrointestinal problems. The trial -- which was double-blinded and placebo-controlled -- found that in patients whose diets were low in FODMAPS, gluten did not produce a specific negative effect.*

"Indeed, patients who believe they have NCGS are likely to benefit from lowering their dietary intake of FODMAPs," Biesiekierski says.

While the underlying causes for non-celiac gluten sensitivity aren't yet understood, it is well known why FODMAPs produce adverse gastrointestinal symptoms. They are not easily digested and absorbed in the small intestine, but bacteria in the large intestine are more than happy to ferment them, producing gas, which results in bloating and flatulence. Common sources of FODMAPs are bread products, chocolate, energy bars that include artificial sweeteners, mushrooms, beans, apples, and anything with high fructose corn syrup.

There are three big takeaways from Biesiekierski's research: 1. If you think you're sensitive to gluten, get tested for celiac disease -- it's a serious condition that's almost certainly underdiagnosed. For each diagnosed celiac patient, at least seven more are undiagnosed. 2. If you don't have celiac disease but are still experiencing its symptoms after eating gluten-containing foods, your problems may result from FODMAPs, not gluten sensitivity. Gluten-free diets can be deficient in fiber and a host of other vitamins and minerals, while simply reducing FODMAP intake can be much healthier and less restrictive. 3. Non-Celiac Gluten Sensitivity (a.k.a. gluten intolerance) may not actually exist. More on that next week.

Source: Biesiekierski JR, Newnham ED, Shepherd SJ, Muir JG, Gibson PR. "Characterization of Adults With a Self-Diagnosis of Non-celiac Gluten Sensitivity." Nutr Clin Pract. 2014 Apr 16. [Epub ahead of print]

Source: Biesiekierski JR, Peters SL, Newnham ED, Rosella O, Muir JG, Gibson PR. "No effects of gluten in patients with self-reported non-celiac gluten sensitivity after dietary reduction of fermentable, poorly absorbed, short-chain carbohydrates." Gastroenterology. 2013 Aug;145(2):320-8.e1-3. doi: 10.1053/j.gastro.2013.04.051. Epub 2013 May 4.

*Section updated 5/15 to more accurately describe the results of the study.