Peanut and Other Legume Allergies

If you are allergic to peanuts, you may have heard that you should avoid other legumes. What should you do? Having a peanut allergy is already challenging enough. Do you really need to determine if the food you eat may contain all other legumes in addition to peanuts?

In order to understand this question, it's important to talk about peanuts and similar foods. Peanuts are a legume similar to other legumes which grow underground such as soybeans, lentils, peas, and beans. They are different than tree nuts, such as cashews, almonds, and walnuts which grow on trees. Intuitively you would think that other legumes should be avoided but tree nuts should be okay, but this is false. While having a co-existing allergy to another legume is similar to the risk of having any type of food allergy along with a peanut allergy, roughly 20% to 60% of people with a peanut allergy also have a tree nut allergy (depending on the study).

If you are wondering whether you need to avoid other legumes with peanut allergy, the answer is "maybe, but no less than you worry about any coexisting food allergies." In fact, most people with peanut allergy are able to eat other legumes without a problem (with the exception of lupine).

Then why are so many people told to avoid legumes? The answer is cross-sensitization.

Allergy tests often show a positive result to more than one legume. This is a result of cross-sensitization, meaning that the similar proteins found in legumes bind to the same allergic antibodies directed against peanut proteins.

Studies vary on how often someone who has a peanut allergy has tested positive for other bean allergies using a blood or prick test — some say 35% to all beans, others say up to 60% are sensitized to soy allergies specifically. Cross-reactivity is also seen with other legumes, in which you will see a reaction. Yet when other legumes are eaten by people who are allergic to peanuts, only 5% react (with the exception of lupin). This is the same percentage of people you would expect to have another food allergy such as a milk allergy. The only way to know if you have a true allergy to another legume is through an oral food challenge (see below.)

The one exception to the above rule is for lupin. Lupin is a legume commonly ground into flour or eaten whole in European countries. There is some level of cross-reactivity between peanuts and legumes, since studies have shown that 11% to 63% of people with peanut allergy experience allergic reactions after eating lupin. Lupin is becoming much more of a problem for those with food allergies.

It's uncommon to find lupin in the grocery store in the U.S., but it is fairly common in some European countries. Those who live outside the U.S. or who travel to Europe should keep this in mind. Apparently, the use of lupin (for example, as a substitute for wheat) is becoming more common in the U.S. as well, especially in packaged foods.

If you are told that you have positive allergy tests to multiple legumes, you should check with your doctor before eating any of these foods. While cross-reactivity rates among legumes are low, your doctor will likely perform an oral food challenge to the legume that you are interested in eating to ensure that you are not allergic.

In an oral food challenge, you eat the questionable food, but with medical supervision. Unfortunately, there is not a reliable way to answer this question with a simple blood test or scratch test.

You may wonder exactly which foods are considered legumes. Foods classified as legumes (and hence having a protein profile which could cross-react with peanuts) include:

• Soy and soybeans
• Beans
• Peas
• Lentils
• Lupin

Peanut allergy has increased drastically over the past decade and now affects one to two percent of the population. Since this phenomena is occurring in the United States and other developed countries but is not seen in many places in the world, the way in which peanuts are processed may underlie some of this increase. Going with that concept, recent studies looking at boiled peanuts may offer an approach to overcoming the allergy according to some researchers. Certainly, you don't want to try this without close supervision by your physician, but this research offers hope that breakthroughs in the management of peanut allergy may be nearing. Until then, avoiding peanuts (and other foods which your allergist feels could be dangerous, (including, at times, legumes), is the only surefire approach to escape the serious reactions and even anaphylaxis which may occur with these allergies. Take a moment to review the peanut allergy diet guide to make sure there aren't any hidden peanut proteins in the foods you eat.