Prevalence of Soy Allergy

Soy protein is widely used by the food industry for its functional benefits such as enhancing moisture reten­tion. For this reason, considerable diligence is required by those who are allergic to soy protein because it is present in many commonly consumed foods. Fortunately, this diligence is required by relatively few individuals as overall, surveys indicate that the prevalence of soy allergy is lowest among the Big 8 food allergens.

Since 2004, the U.S. Food Allergen Labeling and Consumer Protection Act has mandated that the label of a food that contains an ingredient that is protein or is a derived pro­tein from a “major food allergen” must include language noting the allergen included. The 8 foods classified as major allergens are thought to be responsible for 90% of the food-related allergic reactions among Americans.

When the Big 8 was established, relatively little preva­lence data were available. However, as discussed below, over the past 10 years large surveys have provided con­siderable insight into the prevalence of food allergies among Canadian and U.S. children and adults.

The first report in the scientific literature of soy allergy dates to 1934, although in this case the allergic response was the result of airborne transfer of soy allergens among workers in a plant that milled soybeans.¹ More than 30 potential soybean allergen sequences have been identi­fied; 16 of which have been confirmed with some data to support sensitization and elicitation.² However, IgE bind­ing assays using immunoglobulins from soybean sensi­tive individuals reveal that about ⅔ of the total allergenic response is caused by 1 allergen, P34 (Gly m Bd 30K).^3-5

The amount of soy protein required to elicit allergic responses in soy-sensitive individuals is generally much higher than for other food allergens.⁶ In fact, it may be more than an order of magnitude higher than observed for peanut allergy.^7-9 Highly refined soybean oil is exempt from labeling because any residual trace amounts of pro­tein that might be in soybean oil have been shown not to cause reactions in soy protein-sensitive individuals.¹⁰

Allergic reactions to soy are generally considered to be more moderate in comparison to other food allergens, although some cases of anaphylaxis have been reported in the literature. In 1999, Foucard et al.¹¹ concluded that soy allergy has probably been underestimated as a cause of food anaphylaxis. This conclusion was based on a review of medical records of all fatal and life-threaten­ing reactions sent to them by physicians in Sweden over a 3-year period. It was determined that 4 individuals suffered fatal allergic reactions in response to soy pro­tein. However, 1 year later, Sicherer et al.¹² suggested that these reactions were not caused by soy, per se, but instead because the soy-containing foods consumed were con­taminated with trace quantities of peanut protein, lupine, or some other allergen. They noted that if these reactions were due to soy protein, Foucard et al.¹¹ would have iden­tified more fatal soy-allergic reactions in a single country than have been reported in the rest of the world.

Generating accurate prevalence data is challenging because for the most part it relies on self-reported data, that is, survey respondents report whether they are aller­gic to specific foods. In some cases, respondents also indi­cate whether their allergy was diagnosed by a physician, although the method of physician diagnosis is not neces­sarily reported. It is generally recognized that self-report­ed data overestimate prevalence when compared to more rigorous diagnostic methods.¹³ In some cases, surveys can partially control for this discrepancy by assessing wheth­er the report of allergy is consistent with patient history.

Despite the limitations, recent North American surveys provide consider­able insight into the prevalence of soy allergy. As shown in the table, among U.S. and Canadian adults, surveys con­sistently show that the prevalence of soy allergy is lower than the preva­lence of the other 7 foods in the Big 8. For example, the prevalence of milk/ dairy allergy is between about 3 and 41 times greater than the prevalence of soy allergy. Estimates of the prev­alence of soy allergy range from 1 to 6 per 1,000 adults.

The prevalence of food allergy is greater among children than adults, although recent data indicate that food allergies often begin in adulthood.¹⁴ As in adults, soy allergy prevalence among children is the lowest among the Big 8. Children tend to outgrow their allergies, although the rate and extent to which this outcome occursvaries.¹⁵ Estimates in the literature suggest 70% of children outgrow their soy allergy by age 10.^15,16

Finally, concerns about soy allergy appear to be 1 reason many products targeting flexitarians and vegetarians are now made with pea protein rather than soy protein. Although pea protein has not been studied as extensively, it does cause allergic reactions. In fact, concentrating the protein—as is the case for pea protein isolate and pea protein concentrate— may lead to enhanced allergenicity.¹⁷ Canadian researchers recently described 6 cases of severe allergic reactions to foods containing concentrated sources of pea protein.¹⁷

Self-Reported Prevalence of Food Allergy Reported by US and Canadian Adults for Major Food Allergens (percent of population)

REFERENCES

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