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Medical News Today: Are food allergies overdiagnosed?

The millions of dieters out there will know only too well the struggles of maintaining a healthful food intake. But for people with severe food allergies, food choice depends on more than losing a few pounds. It can be a matter of life or death. In recent years, however, studies have indicated that food allergies are being overdiagnosed and overreported, and that many people may be needlessly avoiding certain foods.
[A food allergy sign]
It is estimated that around 15 million children and adults in the U.S. have a food allergy.

There has been a significant rise in the number of people affected by food allergies over the past 20 years.

According to figures from the Centers for Disease Control and Prevention (CDC), between 1997 and 2011, the prevalence of food allergies among adults in the United States rose by 50 percent. Among children, food allergy prevalence is estimated to have increased by 18 percent between 1997 and 2007.

Today, it is believed that as many as 15 million children and adults in the U.S. have food allergies.

Some experts speculate that a combination of environmental, genetic, and lifestyle factors are to blame for the rise in food allergies.

However, another theory is that there has been no increase in the prevalence of food allergies themselves. Instead, experts point the finger at overdiagnosis and overreporting of food allergies, fueled by inaccurate testing methods and misconceptions of what a food allergy really is.

We take a look at both sides of the story.

Food allergy vs. food intolerance

Talking to Medical News Today, allergist Dr. David Stukus, a spokesperson for the American College of Allergy, Asthma, and Immunology (ACAAI), said that confusion remains about the difference between food allergy and food intolerance.

A food allergy is a condition whereby the immune system overreacts to components in certain foods, triggering an allergic reaction.

According to the ACAAI, there are eight foods that make up around 90 percent of all food allergies. These are eggs, milk, peanuts, tree nuts, fish, shellfish, wheat, and soy.

Food allergy symptoms range from mild to severe. They may include wheezing, coughing, shortness of breath, itching, vomiting, stomach cramps, swelling of the tongue, and dizziness.

In rare cases, anaphylaxis may occur. This is a potentially life-threatening reaction whereby symptoms arise in more than one area of the body simultaneously.

“Therefore, it is extremely important to identify if someone has a food allergy so they can be counseled on proper avoidance measures and have an epinephrine autoinjector prescribed,” Dr. Stukus told MNT.

While food intolerance can trigger some of the same symptoms as a food allergy, it is not as severe. Food intolerance is caused by a reaction in the gastrointestinal tract as opposed to an immune system response, causing symptoms such as bloating, abdominal pain, and diarrhea.

“These symptoms may come and go over time and may be related to how much of a given food is ingested. Food intolerances are not immediately life-threatening,” said Dr. Stukus.

What is driving food allergies?

The precise causes of food allergies are unclear, but a number of theories have been proposed.

Dr. Stukus suggests that guidelines recommending against the introduction of allergenic foods – such as peanuts – to children until the age of 2 or 3 years may be behind the reported increase in food allergies.

[A caution sign representing a peanut allergy]
Some experts speculate that environmental factors – such as lack of early-life exposure to microbes – may be behind the rise in food allergies.

This theory is based on recent research indicating that introducing peanuts to children before the age of 12 months may reduce the later development of peanut allergy.

Another proposed contributor to food allergies relates to the “hygiene hypothesis.” This is the idea that lack of exposure to a variety of pathogens early in life may dampen immune system response in later life, leaving us more susceptible to allergies.

“There are other factors shown to be associated, but not necessarily causing a rise in food allergies,” Dr. Stukus told us, “including increased use of antibiotics in children, increased use of antibacterial soaps/sanitizers, birth by cesarean section, and differences in our microbiomes.”

A study published last year, for example, found that children with greater exposure to antibiotics – which are known to affect the balance of gut bacteria – were more likely to develop food allergies.

While these factors could well be fueling a rise in food allergies, some experts believe that the high numbers are more likely to be down to overdiagnosis, largely driven by inaccurate testing.

Skin prick tests ‘inaccurate’ for food allergy diagnosis

To make a food allergy diagnosis, allergists normally begin by asking about a patient’s history of allergy symptoms, followed by a skin prick test and/or a blood test.

The skin prick test involves placing a tiny amount of a suspected food allergen on the forearm or back using a small needle or plastic probe, and monitoring the reaction.

[Skin prick tests]
Skin prick tests are notoriously inaccurate for the diagnosis of food allergy, experts say.

A blood test for food allergy involves collecting a blood sample and measuring the levels of immunoglobulin E (IgE) antibodies for certain foods. High IgE levels for a particular food indicate an allergy.

However, many experts have voiced concerns about the inaccuracy of skin prick and blood tests, noting that they are contributing to food allergy overdiagnosis and causing individuals to needlessly avoid certain foods.

This concern was exacerbated by a recent study, which found that patients who were diagnosed with tree nut allergy based on skin prick tests had no reaction to tree nuts when eaten.

“The skin test is only reliable perhaps 60 percent of the time; many endorse serologic testing as well to increase the sensitivity and specificity of food allergy testing,” Dr. Jonathan Bernstein, a member of the The American Academy of Allergy, Asthma & Immunology (AAAAI), told MNT.

“However, allergy is defined as sensitization with clinical symptoms related to exposure. Many just assume allergy based on a diagnostic test.”

“Skin prick tests for foods have always been associated with very high negative predictive values but poor positive predictive values,” added Dr. Stukus. “We definitely need improved accuracy in our food allergy tests, which is currently under development and/or being studied for validation.”

Oral food challenges ‘should be in routine use’

Talking to MNT, Dr. Bernstein said that he believes oral food challenges should be in more widespread use for the diagnosis of food allergies.

Deemed the “gold standard” for food allergy diagnosis, an oral food challenge involves the patient consuming the suspected allergy-causing foods in varying doses under medical supervision. If the food triggers a reaction, an allergy can be confirmed.

At present, oral food challenges are generally only administered if skin prick and blood tests are inconclusive. Many doctors and allergists shy away from routine use of oral food challenges, fueled by the fear that a patient will have a severe allergic reaction.

However, Dr. Stukus told MNT that “oral food challenges are very safe when performed by board certified allergists who have the experience and skills to treat allergic reactions, should one occur.”

He added that in order to help avoid overdiagnosis of food allergies, we should consider moving away from skin prick and blood tests and moving toward greater use of oral food challenges.

Many people are overdiagnosed when IgE tests are applied broadly, or as screening tools. People should only be tested for food allergies when their history supports the right symptoms, timing of onset in relation to ingestion of a food, and duration of symptoms. If someone is eating a food without any symptoms, they are not allergic to that food.

If someone has a ‘positive’ IgE test, it does not mean they are necessarily allergic and they should not be told to remove food from their diet based upon testing alone.”

Dr. David Stukus

Assume you have a food allergy? You might be wrong

It makes perfect sense to avoid eating a particular food if you have been diagnosed with an allergy to that food, but studies have shown that many of us simply “assume” that we have food allergies.

A 2015 report from the U.S. Food and Drug Administration (FDA) found that between 2001 and 2010, there was a significant increase in the number of adults in the U.S. who reported having food allergies – from 9.1 percent to 13 percent – despite never receiving a medical diagnosis.

[A woman refusing peanuts]
Researchers suggest that many people ‘assume’ that they have food allergies, without receiving a medical diagnosis.

What is more, a study reported by MNT last year found that many parents of children with food allergies presume they are also affected, but only 28 percent actually tested positive for food allergies.

As the authors of the FDA report note, cutting out otherwise healthful foods from the diet may have negative implications.

“[…] since restricting foods and food choices can be detrimental to quality of life and overall health, more focused educational efforts are needed to encourage proper food allergy diagnosis in adults and reverse a potentially adverse health trend,” they write.

It is true that people with a family history of food allergies might be at higher risk themselves, but it is important to get a medical diagnosis before eliminating any food groups.

As the ACAAI advise: “If you suspect a food allergy, see an allergist, who will take your family and medical history, decide which tests to perform (if any) and use this information to determine if a food allergy exists.”

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