Elimination Diets: Do We Know Enough?

Elimination diets, when medically appropriate, can benefit those with food allergies, sensitivities, and intolerances. Several years ago, the United States, Canada, and the European Union (EU) promulgated food labeling regulations to help consumers avoid at least the basic eight allergens (peanuts, soybeans, fish, crustaceans, milk, eggs, tree nuts, and wheat). The Canadian and EU regulations reference additional allergens, including mustard, sesame, sulfites, gluten, mollusks, celery, and lupin. Self-imposed elimination diets may have unintended consequences, however (U.S. News & World Report, 2014).

Today many consumers are opting for alternative protein sources, such as dairy, nuts, seeds, grains, and legumes, for cost-saving and health reasons. Population-based studies suggest early-life vegetable protein consumption may reduce the risk of some forms of cancer (Liu et al., 2014; Bravi et al., 2013), may lower some inflammatory biomarkers (Vallianou et al., 2013), or decrease the risk of cardiovascular disease (Ruiz et al., 2014; Sirtori et al., 2009). 

Considering there are more than 25,000 different wheat cultivars, it is not surprising that wheat, along with other cereal grains, such as corn, rice, and barley, contains several proteins that contribute to dietary allergies (Tatham & Shewry, 2008). Even rice, both raw and cooked forms, which are often considered to be hypoallergenic, contains proteins that may cross react with other cereal grains and some fruit proteins, which prompts an IgE antibody response (Urisu et al., 1991; Asero et al., 2007). Legumes, which represent a high-protein, staple food source for vegetarians, pose risks of IgE-mediated reactions. Lupin is often considered the ninth in category of risk allergens (Moneret-Wautrin et al., 1999). Hemp protein presents numerous allergenic peptides in plant teas and exposure to root, leaf, flower, and bud extracts (Nayak et al., 2013). These allergens appear to be cross-reactive with other allergenic proteins, such as lipid-transfer and thaumatin-like protein (Larramendi et al., 2013), which are common in fruit and vegetables (Fernández, 2003). 

Food-induced allergenic reactions that affect the immune system may be IgE mediated or non-IgE mediated. The more familiar IgE mediated reactions follow a breakdown in oral tolerance, an increase in gut mucosa permeability, and numerous events that contribute to the appearance of classic allergenic symptoms, some of which may be life-threatening. The non-IgE mediated reactions are driven by eosinophils, or T-cell inflammatory responses, and are slow to develop (Verma et al., 2013).

Allergenic proteins impact several autoimmune diseases. One of the common factors to these conditions is a compromised or dysfunctional intestinal epithelium. This single-layer barrier has several complex functions, including nutrient absorption coordination and protection against a typically hostile environment in the gut lumen while maintaining the integrity of internal fluids and tissues (Groschwitz & Hogan, 2009; Fasano, 2012). Permeability of this barrier is modulated through the cells (transcellular) and between the tight junctions (paracellular) (Steed et al., 2010). 

Occludin, claudins, and junctional adhesion molecules (JAMs) are integral transmembrane proteins, which among other factors, are critical in maintaining the integrity of tight junctions (TJ) (Fasano, 2012a). Another important gatekeeper that affects intestinal permeability is zonulin (Fasano, 2012b). Fundamentally, these proteins function as tight junction gates, the expression of which is influenced by dietary protein sources. For example, gliadin, a component of the grain protein gluten, can trigger TJ dysfunction and disassembly via stimulating zonulin release in the gut, the consequence of which is increased intestinal permeability among susceptible individuals (Lammers et al., 2008; Drago et al., 2006). Zonulin release is a consequence of several pathogenic conditions, such as inflammatory diseases, autoimmune disorders, bacterial exposure, and some cancers (Fasano, 2011; Asmar et al., 2002).

It is interesting to note that milk-derived proteins, particularly transforming growth factor β1, a whey component, improve TJ function (Ozawa et al., 2009). It appears this factor activates at least one of the five claudin proteins, which functions to TJ seal pores (Fujita et al., 2008). Earlier research using the Caco-2 cell model indicated β-lactoglobulin can stabilize the TJ via a cascade of enzyme-mediated events (Hashimoto et al., 1998), yet this protein is often associated with cow milk allergy, which may actually depend on processing (López-Expósito et al., 2012).

Elimination diets are often complicated by inadequate consumption of other foods and maintenance of nutritional status. Consumers’ movement to seek non-animal protein sources embraces alternatives for health. An increased understanding of the mechanisms that contribute to food allergies, intolerances, and sensitivities may lead to a rethinking of dietary approaches to maintaining the integrity of the gut barrier.

Roger Clemens, Dr.P.H., CFS,
Contributing Editor
Chief Scientific Officer,
Horn Company, La Mirada, Calif.
[email protected]