A food allergy is an excessive reaction of the immune system triggered by the intake of or contact with certain foods. It causes various allergic symptoms such as redness, itchiness and swelling of the skin, urticaria, coughing and wheezing, vomiting, abdominal pain, diarrhea, and reduced vitality. Symptoms typically appear within minutes to two hours after ingestion. There is a severe allergic reaction called anaphylaxis, which affects multiple body organs, or causes an immediate drop in blood pressure or loss of consciousness. A food allergy often occurs in young children: five to ten percent of children aged zero to one year old have food allergies. Most children leave behind their allergies as they grow up while avoiding food allergens. According to recent studies on allergies, however, the percentage of children with food allergies or those who have experienced anaphylaxis is increasing, while the percentage of children with asthma or atopic dermatitis is decreasing. The most common food allergens are egg, cow's milk, and wheat in Japan. It was found that more than 50 percent of children aged zero suffering from food allergies have egg allergy, and nearly 90 percent of those have egg, cow's milk, or wheat allergy. Some children aged one year or older become allergic to other allergens such as fish, fish egg (mostly, salmon roe), peanuts, shellfish, or fruits, when they have more opportunities to eat these foods as they grow up.

Food allergies often create complications such as infantile dermatitis and atopic dermatitis. About 30 years ago when food allergies started becoming more commonly diagnosed, specific foods were considered as triggers for atopic dermatitis. This is due to the fact that infants aged five to six months with eczema were often sensitized to egg, cow's milk, and peanut (that is, infants had positive specific IgE or positive skin testing results) (however, recent studies show opposite effects). It was also considered that, if a child has an allergic reaction to eggs even though the child has not started a weaning diet and never eaten eggs, the mother's egg intake during pregnancy or breastfeeding is associated with the onset of egg allergy. Therefore, pediatricians at that time recommended mothers to avoid eggs in their diet during pregnancy or breastfeeding, in order to prevent the onset of food allergy or atopic dermatitis in their children, without solid evidence for doing so. However, subsequent high-level research studies revealed that the elimination of specific foods from the diet of pregnant or breastfeeding mothers would not prevent the onset of allergy symptoms in their children ¹. Rather, a strict food elimination diet may cause adverse nutritional effects on mothers and infants. The latest guidelines in Japan and overseas suggest pregnant and breastfeeding mothers should not avoid a specific food in their diet unless they have food allergies.

Then, how about removing eggs or peanuts from the diet of infants with eczema during their weaning period to prevent the onset of food allergies? In Japan, it has been common practice until recently that pediatricians advise mothers having babies aged four to five months with severe eczema not to give eggs until they become one year old. However, recent studies revealed that such a precautionary measure would not prevent the onset of food allergies in infants but increase their risk of developing food allergies. For example, in the UK in around 2000, many parents avoided giving peanuts to their babies, fearing the possibility of peanut allergy. However, a recent study ² shows that the prevalence of peanut allergy among children in the UK is ten times higher than those in Israel where peanut-based foods (such as peanut butter sweets) are introduced earlier in childhood. In order to verify the effect of peanut elimination on the prevention of allergies, Dr. Gideon Lack et al. in the UK conducted a randomized trial that provides a high level of evidence (i.e., the LEAP study) ³. In this trial, they randomly assigned 640 infants aged four months or older but younger than eleven months with egg allergy or severe eczema (that is, who have a high risk of developing peanut allergy) to either the peanut consumption group or the avoidance group. Then, they assessed the prevalence of peanut allergy when these children became five years old. Infants in the consumption group were fed at least six grams of peanut protein per week (equivalent to 24 grams of peanut butter or peanut butter sweets), distributed in three or more meals per week. Among a sample of 628 infants under analysis, the prevalence of peanut allergy was 17.2% in the avoidance group and 3.2% in the consumption group, indicating a significant difference between the two groups. Therefore, it is proved that early peanut introduction reduces the risk of peanut allergy in infants.

Next, we will look into the current status of allergy prevalence in Japan, in particular, egg allergy, one of the most common food allergies in the country. We conducted a research study on egg allergy (i.e., the PETIT study) in Japan. In this study, we randomly assigned infants at high risk for egg allergy, who had been diagnosed with eczema at the age of four to five months, to either the egg consumption group or the placebo group. We observed the prevalence of egg allergy in these infants at twelve months old ⁴. Infants in the egg consumption group were fed 50 milligrams of powdered whole egg (equivalent to 0.2 grams of boiled egg) from the age of six months, and 250 milligrams (equivalent to 1.1 grams of boiled egg) from the age of nine months to twelve months. Among a sample of 121 infants aged twelve months old under analysis, the prevalence of egg allergy was 37.7% in the placebo group (61 infants) and 8.3% in the egg consumption group (60 infants), indicating a significant difference between the two groups. The results of the PETIT study revealed that, as is the case for peanut allergy, the early introduction of egg to infants can prevent the development of egg allergy.

It is considered that the oral intake of specific foods does not trigger food allergies, but rather induces immune tolerance in the gut which prevents the development of allergies. The human body in the first place requires proteins in foods as a nutritional source to function properly. Intestinal immune cells are relatively tolerant to foreign proteins compared to those in other organs, which reduces the risk of developing allergic reactions. Therefore, moderate intake of foods will adequately stimulate immune system in the gut and induce intestinal tolerance (thus, inhibit allergic reactions). To prevent the onset of food allergies in infants, it is essential to start a weaning diet as well as a proper intake of proteins when they are at the age of five to six months, instead of removing food allergens from the diet of mothers or infants. Then, another question arose: if the oral intake of foods reduces the risk of developing allergic reactions, why some infants develop food allergies? Recent studies revealed the mechanism for developing food allergies resulting from an impaired skin barrier function caused by eczema or other factors. I will explain the role of skin barrier associated with food allergies in the next article.

References Cited

• 1. Kramer MS, Kakuma R. Maternal dietary antigen avoidance during pregnancy or lactation, or both, for preventing or treating atopic disease in the child. Evidence-Based Child Health: A Cochrane Review Journal 2014; 9: 447-83.
• 2. Du Toit G, Katz Y, Sasieni P, Mesher D, Maleki SJ, Fisher HR, et al. Early consumption of peanuts in infancy is associated with a low prevalence of peanut allergy. J Allergy Clin Immunol 2008; 122: 984-91.
• 3. Du Toit G, Roberts G, Sayre PH, Bahnson HT, Radulovic S, Santos AF, et al. Randomized trial of peanut consumption in infants at risk for peanut allergy. N Engl J Med 2015; 372: 803-13.
• 4. Natsume O, Kabashima S, Nakazato J, Yamamoto-Hanada K, Narita M, Kondo M, et al. Two-step egg introduction for prevention of egg allergy in high-risk infants with eczema (PETIT): a randomised, double-blind, placebo-controlled trial. Lancet 2017; 389: 276-86.