By Louise D. Metz, MD
Gluten-free diets have dramatically increased in popularity in the last decade, and over $15 billion was spent on sales of gluten-free foods in the US in 2016. It has become commonplace to see gluten-free options on menus at restaurants and grocery stores. Many people report following a gluten-free diet for health reasons, often to address gastrointestinal conditions or symptoms. Does the science support the widespread adoption of gluten-free eating?
Celiac disease is a genetic gastrointestinal disorder affecting less than 1% of the US population that is characterized by immune-mediated damage to the small intestine induced by dietary gluten, a protein found in wheat, rye and barley. This small bowel damage causes malabsorption that leads to diarrhea, bloating, and abdominal pain, as well as long term complications, including vitamin deficiencies, anemia, and osteoporosis. The treatment for this condition is complete elimination of gluten from the diet, which then leads to healing of the small intestine and normal absorption of nutrients. There are also individuals who have a true wheat allergy, which can cause hives, throat swelling, wheezing, or anaphylaxis due to the gliadin protein found in wheat. For those with celiac disease and wheat allergies, eliminating gluten is essential for their health.
Despite the rarity of celiac disease, many individuals report experiencing sensitivity to gluten products, and therefore minimize or avoid gluten in their diets. In fact, 20-45% of adults who report food sensitivities will identify gluten as a trigger. The term non-celiac gluten sensitivity has been used to describe a syndrome of bloating, abdominal pain, and changes in bowel habits after ingestion of gluten in the absence of celiac disease. Some individuals also report fatigue, body aches, and foggy mind along with the gastrointestinal symptoms. Though these symptoms are often attributed to gluten ingestion, the scientific literature points to other causes of these symptoms apart from gluten intake.
There are other components of wheat called fructans that can contribute to the symptoms in those who experience gastrointestinal (GI) sensitivity when they eat wheat products. Fructans, or fructo-oligosaccharides, are a type of carbohydrates found in wheat and multiple other foods. They are not well-absorbed in the small intestine, have fermentable components and pull water into the colon, which can contribute to gas production and bloating. A recent randomized controlled trial showed that in patients with self-reported non-celiac gluten sensitivity, dietary fructan ingestion was associated with an increase in GI symptoms, while dietary gluten ingestion was found to have no difference in GI symptoms compared with placebo.
The fructans, along with certain other carbohydrates, are known as the FODMAPs (fermentable oligo-, di-, and mono-saccharides, and polyols), and have been found to be associated with GI symptoms in patients with Irritable bowel syndrome (IBS). IBS is a type of functional gastrointestinal disorder (FGID) characterized by recurrent episodes of abdominal pain with associated changes in bowel habits. Individuals with IBS have visceral hypersensitivity (increase in sensation when exposed to stimuli in the gut), intestinal inflammation, and altered gut bacteria, all of which contribute to the GI distress that can occur in response to eating and digesting some foods. However, the symptoms that occur with FODMAP foods are not a marker of intolerance of these carbohydrates, but rather are a function of the breakdown of these foods in the setting of abnormal gut function. It is also important to note that IBS symptoms can occur after ingestion of any type of food, and are not limited to exposure to FODMAP foods.
Given these other reasons for GI sensitivity apart from the actual gluten protein, the syndrome termed non-celiac gluten sensitivity is likely not a true intolerance to gluten, but rather a form of IBS or other functional GI disorder. Therefore, addressing the underlying pathophysiology of the functional GI symptoms can often be a more effective solution for GI sensitivity than eliminating foods (either gluten or FODMAPs foods) from the diet. In fact, elimination diets or any other forms of restriction of food intake can sometimes make GI symptoms worse. Malnutrition can break down the intestinal lining and alter the gut microbiome (normal gut bacteria) leading to progressively worsening stomach and intestinal functioning. A wide variety of nutrient intake, as well as adequate quantity of food, are essential for gut health.
If gluten-free diets are not the answer, what else can be done to help GI sensitivity and Functional GI disorders? In addition to adequate nutrition, probiotics and certain antibiotics can be useful to help realign the normal bowel bacterial flora, thereby decreasing bloating, pain and changes in bowel habits. Dietary fiber or fiber supplements can be helpful for some individuals, and can also assist in maintaining the gut microbiome. In addition, targeting the gut-brain axis (the signaling between the gut nervous system and the central nervous system), which has been shown to be dysregulated in the setting of IBS, can be very important for symptom improvement. The gut-brain connection can be addressed through stress reduction, mindfulness and somatic-based therapy, as well as certain medications.
Despite the common instinct to eliminate gluten products from the diet when abdominal pain, bloating and bowel changes occur, the science does not support this dietary restriction in individuals without celiac disease. When GI symptoms occur with ingestion of gluten-containing or other foods, it can be helpful to address the underlying impairments in the GI tract rather than naming certain foods as the problem. Our gastrointestinal tracts are designed to digest and utilize a wide variety of foods, though this complex system that is so crucial to our overall health and well-being sometimes needs some additional support to function smoothly.