Half of the people who think they have food allergies actually don't

Food allergies can be confusing to figure out. Once a food item has wrecked havoc on any part of your body, whether its an itchy rash or a bout of diarrhea, its easy to dismiss that reaction as an allergy. But how many of us actually have true food allergies? A recent study suggests that number is far less than what you might think.

Even though common wisdom holds that allergies of all kinds have been on the rise in recent years, researchers actually have very little data on allergies in adults since many of them never get diagnosed by a physician. Some studies have attempted to use hospitalization data as a proxy, but that only picks up people with sufficiently serious allergies to go to the ER for anaphylaxis. Another study used data from NHANES, a massive national survey study that occurs every few years, to look at actual blood test results.

This new study, out last week in the journal JAMA Network Open, took a far broader approach, and focused solely on food allergies: Researchers based out of Northwestern University surveyed some 40,443 American adults and asked them a series of questions designed to figure out how many people actually had food allergies versus how many just thought they did. What they found? Although one in five people surveyed reported having an allergy, only about one in 10 actually does.

To understand how they came to this conclusion, we first have to understand the difference between a true food allergy and a food intolerance, both of which can seem similar to the untrained eye.

Let’s start with an example pretty much everyone is familiar with: dairy. Most people know someone who’s lactose intolerant. These individuals lack the enzyme lactase (to varying degrees) that allows them to break down lactose, the sugar in milk. If they consume a large amount of lactose-containing dairy, the undigested lactose builds up in the gut causing uncomfortable symptoms like bloating and diarrhea until the stuff passes through the digestive tract. Though uncomfortable, that gastrointestinal distress is never life-threatening. As such, they can absolutely drink a milkshake (though they will likely pay for it later).

On the other hand, you probably don’t know someone with a milk allergy because that’s much less common. But if you do, you know they can't drink milkshakes. That’s because they have a true allergy, which means the root of the problem is not in their digestive systems, but rather in their immune systems. Allergists call these responses “IgE-mediated” because, well, they’re mediated by a protein called Immunoglobulin E. IgE is an antibody that your immune system produces whose job it is to identify intruders like parasites. People with allergies accidentally produce IgE molecules that identify harmless proteins like those in peanuts, shellfish, or milk as being dangerous. That means upon ingestion, IgE are like the alarm that kicks up a massive immune response, recruiting histamines and other immune cells that kill the invader. It's this overreaction that causes your throat to close or your blood pressure to drop precipitously, or any of the other allergic symptoms that transcend one bodily organ and extend into the respiratory system or perhaps the skin or cardiovascular system. This response can absolutely be life threatening.

Source: popsci.com

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