Peanut Allergies, Soybeans, and Legumes

Soybeans and other legumes likely are fine, but watch out for lupin

Jar of nuts

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If you're allergic to peanuts, which are a legume, you probably don't need to avoid most other legumes such as soybeans, peas, and beans. Generally speaking, you can confidently add soy and other beans to your diet.

However, your allergist may advise you differently depending on your individual test results and family medical history. In addition, there's one legume—lupin—that you most likely should avoid, since there's a high likelihood of a reaction to lupin in people who are allergic to peanuts.

Are Peanuts Nuts?

Walnuts, pecans, cashews, hazelnuts, and almonds all grow on trees and are classified as tree nuts. Many people believe that peanuts are also a nut—after all, they have the word "nut" in their name. However, that's not correct.

Peanuts are in fact a member of a plant family called legumes. In general, legume pods grow underground and contain edible seeds. Other members of the legume family include peas, beans, and soybeans.

Though peanuts and tree nuts have many botanical differences, they are often grouped together because of their similar nutrition profiles and dietary uses. They also share some allergen proteins in common, which is why people are often allergic to both.

While peanut allergy and tree nut allergy are two different allergies, some people are allergic to both. This is due to a phenomenon known as cross-reactivity.

Even though peanuts are more closely related botanically to legumes than they are to tree nuts, people with peanut allergies are at greater-than-normal risk of tree nut allergy. For this reason, many people with peanut allergies are advised to avoid tree nuts as a precaution.

Potential Legume Allergies

There is not a high level of cross-reactivity between peanuts and other legumes like beans, peas, and soybeans. Overall, your risk of being allergic to other legumes, such as soybeans, does not increase simply because you are allergic to peanuts.

If you have a peanut allergy, your allergist may have you take a skin prick test to see how your body reacts when exposed to allergen proteins that are found in other legumes. Often, the test will yield a positive result for legumes that you have never had any trouble eating before.

In one study, 35% of people with a peanut allergy tested positively for allergy to other legumes. However, just 5% of people had allergic symptoms upon exposure to those legumes. As a next step, your allergist may conduct an oral food challenge to narrow down which legumes, if any, you should avoid eating.

Lupin May Cause a Reaction

One type of legume, lupin, may pose higher risks than other legumes for those who have peanut allergy. Lupin (also known as lupine) is a legume that's common in Europe, where it's used as flour in baked goods.

Lupin is becoming more common in the U.S., where lupin flour is used occasionally in gluten-free pasta and baked goods. Other products that may contain lupin are:

  • Alternative meat products, such as vegetarian sausage
  • Dairy-free ice cream or products that substitute lupin for soy or cow's milk
  • Deep-fried vegetables, such as onion rings or fried pickles
  • Lupin hummus
  • Tempe, crumb, or lupin flakes
  • Pre-packaged foods

Studies have shown that up to half of people with peanut allergies experience an allergic reaction when they consume lupin.Therefore, you should talk to your doctor before trying lupin, and watch for it on food labels. You may also see it labelled as lupin flour, lupinus, lupine, lupini, or lupine beans.

When to Call a Doctor

Symptoms of anaphylaxis can begin within seconds to minutes of eating a food. Breathing difficulties, trouble swallowing or speaking, swelling of the tongue, a tight chest, and dizziness are all symptoms of anaphylaxis and should be treated as a medical emergency.

Soy Allergies

For adults, soy allergy as an isolated allergy is not common, nor is soy-related anaphylaxis. More often, soy allergy is detected in infants and is typically outgrown by the time children are 10 years old.

The allergen triggers in soy and peanuts are not related, and having an allergy to soy does not increase your risk of having a peanut or tree nut allergy. Keep in mind that it's common for people who have a peanut allergy to test positive for soy allergy as well, but this does indicate that they will have allergic symptoms when exposed to soy.

Soy Formula and Peanut Allergies

It's not clear whether drinking formula made from soy milk might contribute to peanut allergy. 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.

In a study involving 13,971 children, a total of 49 children had a history of peanut allergy, which doctors confirmed 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.

However, another study published in the Journal of Clinical Allergy and Immunology suggested that the milk allergies that prompted parents to switch to soy-based 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.

In 2020, the U.S. Department of Agriculture (USDA) and Health and Human Services (HHS) released dietary recommendations for infants and children under the age of 2. According to the guidelines, to decrease the risk that an infant will develop a peanut allergy, the infant should be introduced to potentially allergenic foods, such as soy, beginning at 6 months old.

A Word From Verywell

For the time being, the question of whether or not 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​ babies at high risk for developing food allergies be exclusively breast-fed for at least four months and up to six months. If that's not possible, pediatricians recommend using hypoallergenic infant formula, not soy formulas, for babies at risk for or with a history of food allergies.

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