Food allergies are a serious public and personal health concern. Six common foods—milk, eggs, peanuts, tree nuts, fish, and crustacean shellfish—account for nearly 90% of food allergy reactions.
Fundamentally, there are two types of food sensitivities or adverse reactions associated with exposures to food allergens—food allergy or food intolerance. The body’s adverse response to food can be caused by mechanisms involving either the immune system or numerous systems outside of the immune system, typically the digestive system. The latter is often referred to as food intolerance.
Food allergens, usually proteins, occur naturally in all foods. In sensitive individuals, exposure to these food proteins stimulates cells that result in specific immunologic reactions. A food allergy reaction may be mediated by IgE antibodies, a specific type of immunoglobulin made in response to offending proteins, or not mediated by IgE but rather through specific kinds of cells.
The concept of oral tolerance has gained attention in the medical and scientific community. Recent evidence suggests the onset of food allergy may reflect intolerance to dietary or foreign proteins. The gastrointestinal (GI) tract is an important barrier to foreign proteins. The GI tract not only represents a large surface area through which we absorb nutrients provided through foods, it is a significant component of the immune system. If this immune system is compromised or immature, there is an increased risk of developing food allergies. For example, while about 2% of ingested food allergens are absorbed and transported without modification in the mature gut, the GI tract in susceptible individuals may have an increased permeability and altered intestinal bacteria profile.
A novel approach in treating food allergy is through the induction of oral tolerance. Limited research suggests early introduction of allergenic proteins such as those in peanuts may actually reduce the risk of allergy (De Toit, G. et al., 2008). In this case, it appears that in some susceptible individuals, high level of exposure to peanuts, such as through peanut butter in the home, may promote sensitization, whereas low-level exposure may be protective (Fox, A.T., 2009). These kinds of observations are inconsistent and controversial, however.
The impact of food processing, such as the use of food enzymes and heat to hydrolyze or break down allergenic proteins, requires additional research. There is limited evidence that food-grade enzymes may reduce the allergenicity of some milk proteins, such as β-lactoglobulin in the whey fraction, and may reduce the phytate content of grains. In addition, some heat treatments, intended to assure food safety, may denature allergenic proteins such as those in some vegetables (Mills, E.N.C. and Mackie, A.R., 2008). A recent evaluation of food processing indicates there is a dearth of scientific research on this topic, which, in part, reflects the complex nature of a food matrix and the individuality of allergenic response (Mills, E.N.C. et al., 2009). This issue is further complicated by our naive understanding of cross reactivity of allergenic proteins and the fact that many of these proteins occur naturally in foods. Another complication is that while some proteins are partially denatured during various processing environments, others are resistant to structural modifications and potential reduction in allergenicity. It is important to note that several plant-derived proteins present similar structural characteristics and possibility of allergenicity similar to those found in some animal proteins. Some of these proteins are also thermally stable and resistant to hydrolysis (Breiteneder, H. and Mills, E.N.J., 2005; Sathe, S.K. and Sharma, G.M., 2009).
There is also evidence that some food processing methods may increase the allergenicity of foods (Sathe, S.K. and Sharma, G.M., 2009). For example, some research suggests that peanut roasting may not alter the allergenicity of peanut proteins (Mondoulet, L. et al., 2005), whereas others indicate the roasting and possibly the maturity of the peanut may increase the presence of antibody-binding epitopes, or those protein segments responsible for an allergic reaction (Pomés, A. et al., 2006).
The National Institute of Allergy and Infectious Disease will publish an update for “Guidelines for the Diagnosis and Management of Food Allergy” this year. While this publication is directed to health care professionals, the concepts of identifying and managing food intolerance and food allergy are well presented and should be useful for those interested in these important areas.
References for the studies cited in this column are available from the authors.
by Roger Clemens, Dr.P.H.,
Scientific Advisor, ETHorn, La Mirada, Calif.
by Wayne Bidlack , Ph.D.,
Professor, California State Polytechnic University, Pomona