Lack of a Standard Definition for Gluten Sensitivity
The first major problem is that although a clear definition for celiac disease exists (Table 1), there is none for gluten sensitivity. Until recently, the term gluten sensitivity was used interchangeably with celiac disease or gluten intolerance in the medical literature. Although people with celiac disease or 'gluten-sensitive enteropathy' are gluten sensitive, the latter term is emerging as a separate condition. Although almost 200 proteins are in the gluten family, 'gluten' is commonly referred to as a protein composite (gliadin and glutenin) found in wheat, but also in rye, barley and oats.
It should also be noted that food sensitivities or adverse food reactions are nonspecific terms encompassing food allergies (immune-mediated) and food intolerances (nonimmune-mediated). Immune-mediated reactions can be further broken down into IgE-mediated and non-IgE-mediated reactions, the latter includes both celiac disease and gluten sensitivity. Unlike food allergies, food intolerances are not due to an immune reaction, but rather an internal problem of processing the food or food component(s) (e.g., food additives, tyramine and aspartame). A myriad of mechanisms exist and include, but are not limited to, disorders of digestion and absorption (lactose or fructose intolerance), inborn errors of metabolism (phenylketonuria and galactosemia), as well as toxic (food poisoning, tyramine from aged cheeses and theobromine from chocolate) and idiosyncratic reactions (food additives).
Celiac disease is also known as celiac sprue, nontropical sprue, gluten-sensitive enteropathy and gluten-induced interopathy. The classic definition is that gluten triggers the immune system, causing small-intestinal epithelial cell damage resulting in malabsorption. However, Table 1 shows that some newly diagnosed patients suffering from celiac disease do not manifest signs and symptoms of malabsorption or that digestive complaints are either absent or of secondary importance. Some patients experience visible symptoms and some do not because of very wide variations in sensitivity. The diagnosis may sometimes be reached after studying chronic dyspepsia, gastroesophageal reflux or extraintestinal manifestations, such as immune-mediated thyroid problems.
Nonceliac Gluten Sensitivity or Gluten Sensitivity
Nonceliac gluten sensitivity is a separate problem from celiac disease, which emerged prior to 2008. Until this time, the medical establisment only officially recognized gluten as being problematic in people with celiac disease. A review by Newnham found that very few studies exist to suggest otherwise, with one exception: a double-blind, randomized, placebo-controlled rechallenge study of patients with irritable bowel syndrome but without celiac disease. These patients experienced alleviation of symptoms following a gluten-free diet. Previous researchers have reported that approximately 20% (24 out of 120 subjects) of patients with irritable bowel syndrome experience food sensitivities and find relief when eliminating wheat and dairy from their diets.
The current status in establishing a standard definition for gluten sensitivity is that its very name, definition and diagnosis remain in flux as researchers search for clarification. It is clear that many health-insurance companies lack both the name and reimbursement coding for gluten sensitivity.
Expert Rev Gastroenterol Hepatol. 2012;6(1):43-55. © 2012 Expert Reviews Ltd.