Peanut Allergies and Other Legumes

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Question: I'm allergic to peanuts. Do I also need to avoid other legumes like soybeans, peas and beans?

Answer: For the most part, no, although your allergist may advise you differently depending on your individual test results and family history.

Peanuts, Soy and Other Legumes

Peanuts are a member of a plant family called legumes, which includes peas and beans. (Curiously, although people with peanut allergies are at greater-than-normal risk of tree nut allergy, and for this reason many people with peanut allergies are advised to avoid tree nuts as a precaution, peanuts are not closely related to true nuts botanically.)

Often, people who are allergic to one food are allergic to closely related foods due to some of the same allergenic proteins being in both foods. This phenomenon is known as cross-reactivity. One common example is that people who are allergic to shrimp are often allergic to other shellfish, like crabs and lobster.

In the case of peanuts, there does not appear to be a high level of cross-reactivity between peanuts and other legumes like beans, peas, and soybeans. (One type of legume, lupine, may pose somewhat higher risks than other legumes.) Although peanuts are a member of the legume family, your risk of being allergic to other legumes, such as soy, does not rise simply because you are allergic to peanuts.

Can Soy Sensitize Babies to Peanuts?

Recent studies have shown contradictory results as to whether early introduction of soy milk or soy formula can sensitize children to peanuts and make them more likely to develop a peanut allergy.

Some studies have indeed shown that infants fed soy formula are more likely to develop peanut allergies. In a 2003 study involving 13,971 children, a total of 49 children had a history of peanut allergy, and doctors confirmed peanut allergy through a peanut challenge in 23 of the 36 children tested.

The researchers found that these peanut-allergic children were 2.6 times more likely to have consumed soy formula or soy milk. Other factors associated with developing peanut allergy included having a rash over joints or skin creases, and having an oozing, crusting rash. (In that study, children who had used skin preparations that included peanut oil had the biggest odds of later developing peanut allergy: a nearly seven-fold increase.)

But a June 2008 study in the Journal of Clinical Allergy and Immunology suggested that the milk allergies that prompted parents to switch to soy formulas may have themselves caused the increased number of peanut allergies in soy-fed babies in previous studies. Once the researchers adjusted for these factors, the association between soy formula and peanut allergy disappeared.

The Bottom Line on Peanuts, Soy and Other Legumes

For the time being, the research question on whether babies and children at risk for peanut allergy should consume soy is not completely resolved, and parents should follow their pediatricians' recommendations on feeding their infants.

In general, the American Academy of Pediatrics recommends that hypoallergenic infant formula, not soy formulas, be used for babies with a history of food allergies.

Sources:

Koplin, Jennifer, et al. "Soy Consumption is Not a Risk Factor for Peanut Sensitization." Journal of Allergy and Clinical Immunology. June 2008 121(6): 1455-59.

Lack G et al. Factors associated with the development of peanut allergy in childhood. New England Journal of Medicine. 2003 Mar 13;348(11):977-85.

Sicherer, Scott H. and Hugh A. Sampson. "Peanut Allergy: Emerging Concepts and Approaches for an Apparent Epidemic." Journal of Allergy and Clinical Immunology. Sept. 2007 120(3): 491-503.

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