Is It the Gluten or the FODMAPs? – A Confusion, Explained

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A common misconception about the low FODMAP diet is that it is a gluten-free diet. This is understandable as gluten-containing grains - wheat, barley, and rye - are greatly reduced or avoided during the elimination phase. For some people, these foods trigger common digestive symptoms (gas, bloating, abdominal pain, constipation or diarrhea). What is it in these foods that is responsible for the symptoms? Let’s dig in.

Gluten vs Fructans

Gluten is the main protein in wheat, barley and rye and needs to be avoided by people diagnosed with celiac disease. People with non-celiac gluten sensitivity (NCGS), a newly recognized condition that occurs when someone has a reaction from eating gluten but does not have celiac disease or a wheat allergy, also feel better when avoiding these grains and their products. These conditions are typically diagnosed by a gastroenterologist. Finally, people with a wheat allergy need to avoid all varieties of wheat (including spelt, kamut, einkorn, farro/emmer and triticale).

Fructans are a type of carbohydrate in gluten-containing grains, one of the FODMAPs (within the larger category of oligosaccharides, the “O” in FODMAP – more on this topic in a future article of my FODMAP Series). The common confusion comes from the fact that both gluten and fructans co-exist in wheat, barley and rye. The reason why these grains are reduced in the low FODMAP diet is that the fructans are poorly digested in people with IBS and may trigger symptoms. During the elimination phase, gluten-free grains like rice, quinoa, buckwheat and millet become a staple but small amounts of wheat can still be included. The main wheat-containing food allowed is true sourdough bread, as the fructans have been “digested” by the live cultures during a long process of fermentation, which reduces the fructan content of the bread. Soy sauce and even one small slice of regular wheat bread are usually tolerated and considered low FODMAP. In conclusion, the low FODMAP diet is not a gluten-free diet.

Not all gluten-free products are low FODMAP

During the elimination phase of the low FODMAP diet people rely on gluten-free grains and some gluten-free alternatives to bread, pasta, crackers and cookies assuming these are low in FODMAPs. It is important to point out that not all these packaged products are necessarily low in FODMAPs. When looking at a gluten-free product you need to become an expert label reader. Although the main flours used are low FODMAP (rice, tapioca, cassava), there are very often high FODMAP ingredients such as honey, agave, pear or apple juice (used as sweeteners), inulin or chicory (added to increase the fiber content) and others.

Take home message

Many people report feeling better on a gluten-free diet but don’t necessarily know why. Is it because they are sensitive to gluten, or the fructans? If you are one of them, I strongly encourage you to get a proper diagnosis first. If celiac disease or NCGS are diagnosed, then you will know that you need to avoid gluten-containing grains and their products. If you are found to have a wheat allergy, you will need to avoid all wheat products.

If you don’t have any of these conditions or continue to have symptoms on a gluten-free diet, the fructans (FODMAPs) may be to blame. Working with a dietitian to identify the source of the problem may help you liberalize your diet and find that you don’t need to unnecessarily avoid all gluten-containing grains and products. Interestingly, a recent study from Monash University (Biesiekierski et al, Gastroenterology 2013) found that only a small percentage of the subjects who had both IBS and NCGS were indeed sensitive to gluten (8%) but all felt better while eating a low FODMAP diet, suggesting that the FODMAPs had the greatest impact in their digestive symptoms.