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Harvard Commentaries
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Harvard Commentaries
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Food for Thought Food for Thought
 

Allergies: When Nuts Are Not Healthy


January 16, 2013


By Julie Redfern, R.D., L.D.N.
Brigham and Women's Hospital

We've been told that nuts are a "super food" of the decade. These little nuggets are rich in protein, fiber, folic acid and vitamin E. However, for some people they bring disaster. In the United States, 1.5 million people are severely allergic to peanuts alone. Half the people allergic to peanuts are also allergic to tree nuts. The number of children with peanut allergies has increased dramatically over the past couple decades. It may be hard to explain why, but this increase does parallel an increase in allergic diseases of childhood.

What Are Food Allergies?

Food allergies are immune system reactions to foods. Reactions can be mild to severe, in some cases causing life-threatening anaphylactic shock. These reactions are referred to as an "allergic cascade." First the allergic food, such as peanuts, enters the body by ingestion, inhalation or skin contact. The body senses the protein in peanuts as a foreign invader. In response to the threat, IgE antibodies are released into the bloodstream. The IgE triggers cells to release substances called histamines that cause allergy symptoms.

Multiple body systems can be involved in the allergic response. A typical reaction starts with hives — raised spots on the skin that turn red and itch. This may be followed by swelling in various parts of the body, including the breathing passages.

More severe reactions might cause difficulty in breathing, nausea, vomiting and abdominal pain. The most severe reaction, anaphylaxis, results in very low blood pressure (shock) that requires emergency treatment. Severely allergic individuals need to carry self-injectable adrenaline (an epinephrine shot such as the EpiPen) to slow down the cascade of symptoms.

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How Can You Tell If You're Truly Allergic?

Clinicians use four methods to help diagnose food allergies:

  • Skin test — The skin is pricked and a potential allergen is applied. This may involve risk.
  • RAST (Radioallergosorbent Test) — This blood test detects antibodies. It is less accurate than the skin test, but safer, and therefore recommended for young children and people with skin diseases such as eczema.
  • Oral food challenge — The patient tries several types of foods to see if a reaction occurs. Capsules are used to hide the identity of the foods. This is considered the most effective test, but time-consuming and may involve risk.
  • Elimination diet — Peanuts or other potential allergens are removed from the diet for several weeks, then slowly reintroduced.

Consult your physician if you think you may have a food allergy.

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Why Are Peanut Allergies Increasing?

While several theories abound, there is no conclusive explanation. Possible explanations include:

  • Early exposure when the immune system is immature
  • Roasting peanuts — Roasting makes peanuts more likely to cause allergic reactions because it changes the structure of the peanut protein and makes peanuts harder to digest.
  • Increased use of topical creams that contain peanut oil
  • Use of soy formulas — Both soy and peanuts are legumes, and people with peanut allergies can be allergic to other legumes. This is referred to as a cross-reaction.
  • Living in too sterile an environment — The hygiene theory holds that an excessively clean environment can affect our immune systems, making us more susceptible to allergic and autoimmune disorders. Research is needed to determine if the hygiene theory plays a role in nut allergies.

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Should Pregnant or Breastfeeding Women Limit Exposure?

Exposure to peanuts very early in life appears to increase the risk of developing allergy to peanuts. The Avon Longitudinal Study, a British study of 13,971 preschool children, was designed to collect information from early pregnancy throughout childhood regarding the incidence of peanut allergies. Results did not show any definitive evidence that peanuts in a pregnant woman's diet cause an increased sensitivity to peanuts for the fetus. Further tests showed no peanut-specific IgE detected in cord blood.

Instead, other explanations for peanut allergy have been proposed, including family history of peanut allergy, skin exposure to preparations containing peanut oil (especially if skin rashes or breaks in the skin are present), and early exposure to soy protein.

Women who are breastfeeding may want to avoid eating peanuts. Some studies have shown that peanut protein is secreted into breast milk, which may sensitize at-risk infants.

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How Can You Manage Nut Allergies?

Obviously, managing nut allergies will depend on how mild or severe the allergies are. Mild reactions that cause hives, sneezing, runny nose or gastrointestinal upset may improve with antihistamines. Bronchodilators may help relieve shortness of breath and wheezing. Epinephrine, a synthetic form of adrenaline, is a powerful bronchodilator, reserved for severe anaphylactic shock.

Peanuts are legumes, as are peas, beans and lentils. Tree nuts are large, edible seeds of trees, some of which include cashews, almonds, pecans, walnuts, beechnuts and pistachios. The most successful method of managing peanut or tree nut allergies is to avoid them, including hidden sources. Besides the obvious sources of peanuts, peanut protein can be found in hydrolyzed plant or vegetable protein; cereals; ice cream and other desserts; Chinese, Indonesian or Thai foods; salad dressings; curry and satay sauces, as well as topical creams and shampoos. This is not an all-inclusive list.

Always read packaging labels carefully for information on the ingredients. If you are unsure about the ingredients, the best bet is to contact the manufacturer. Highly allergic people need to avoid anything or anyone who comes in contact with peanuts.

When a peanut or nut allergy occurs in a child, it impacts the entire family and the extended community. Because severe reactions can be life-threatening, children with peanut allergies are faced with challenging food and social restrictions. Children who are highly allergic must avoid contact with or inhalation of any peanut products.

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What Foods Can Replace the Nutrition in Nuts?

When peanuts cannot be a part of your diet, the foods below will help you get the nutritional benefits they provide:

  • Green leafy vegetables, orange juice and fortified cereals — for folate
  • Olive oil, olives, canola oil and avocadoes — for healthy fats
  • Chicken, red meat, beans, eggs, cheese and milk — for protein
  • Whole grains, fresh fruits and vegetables — for fiber
  • Wheat germ, green leafy vegetables (spinach), vegetable oils and egg yolks — for vitamin E

For more information on food allergies, see the Food Allergy and Anaphylaxis Network (FAAN) website, www.foodallergy.org.

Julie Redfern, R.D., L.D.N., is a registered dietitian in the Nutrition Consultation Service at Brigham and Women's Hospital. She specializes in nutrition counseling for the Obstetrics and Gynecology Department. She is a graduate of the University of Vermont and completed her dietetic internship at the University of Cincinnati Medical Center.

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