Ask the Allergist
What Is The Difference Between A Food Allergy And Intolerance?
What's the difference between a food allergy, intolerance, or sensitivity?
It's really important to clarify distinctions between a food allergy and intolerance and a sensitivity. And when I see patients in the office, I always spend time just defining what these are, because that really sets the stage for the role of testing, the need for elimination diets and management and prognosis.
Food allergies are caused by the immune system. There's immediate types of allergies, which are caused by the Immunoglobulin E antibody known as IgE, and this will cause rapid onset reproducible symptoms every time that food is eaten. So, if you're concerned about, say, a milk allergy, then you really should be having symptoms when you eat cheese, when you eat yogurt, ice cream, or drink milk. These symptoms can range in severity, as well as types of symptoms. We often will see combinations of big red itchy hives, swelling, rashes, itching. It can produce, vomiting, coughing, or anaphylaxis, which is a severe, rapidly progressive, systemic allergic reaction that involves more than one part of the body.
If you're eating a food and not experiencing those symptoms, it's very unlikely that you're allergic. There are more rare causes of delayed onset food allergy, one of which is called food protein-induced enterocolitis syndrome (FPIES). And this causes delayed onset profuse vomiting, like in the movie The Exorcist. So, this typically occurs in young infants between six and 12 months of age at first, and it can occur to a wide range of foods, including things like cow’s milk, or soy, or rice, or even grains, and vegetables. And the story typically goes, they eat the food. They're completely fine. Three hours later, they start to have profuse vomiting and sometimes diarrhea. This occurs in the absence of hives, and swelling, and anaphylaxis. There are no good diagnostic tests to diagnose that, but it's important to understand that the clinical history should be reproducible every time that food eaten.
Then we have non-allergic or non-immunologic symptoms due to food intolerances. So, this is not part of the immune system. This is difficulty with digestion. Food intolerances can come and go over time or it may vary based upon the type of food you eat or the amount of food you eat. The most common example would be lactose intolerance, where people lack the ability to digest this simple sugar called lactose, which is present in dairy products. If you eat dairy products, it passes through undigested. Causes a lot of discomfort. Can cause bloating, diarrhea, gassiness, and things like that. There are no easily available commercial tests to diagnose food intolerance. So often times, we'll take a clinical history. If it suggests specific food intolerances, we’ll recommend a 2-to-4-week strict elimination diet with careful observation, whether the symptoms that were previously attributed to that food resolve or not. If the symptoms don't resolve, it probably wasn't that food. If the symptoms do resolve, we recommend eating that food again to see if the symptoms come back again. This is the best way to really figure out whether somebody has a true food intolerance.
And then lastly, we have the term called food sensitivity. Well, unfortunately, there really is no consensus expert criteria for how to diagnose a food sensitivity. And unfortunately, if you spent any more than 30 seconds online, you'll see a lot of marketing behind food sensitivity tests and things like that. Well, often times they attribute all kinds of vague symptoms that had nothing to do with ingestion of specific foods to having a “food sensitivity.” And then they will sell very expensive at home food sensitivity test kits which aren't validated and really don't indicate anything other than food you've eaten in the past. So, when it comes to food sensitivity, you know, if you have concerns, please, please discuss with your personal doctor.
David Stukus, MD, is a Professor of Clinical Pediatrics in the Division of Allergy and Immunology, Director of the Food Allergy Treatment Center, and Associate Director of the Pediatric Allergy and Immunology Fellowship Program at Nationwide Children’s Hospital and The Ohio State University College of Medicine. He is board certified in allergy/immunology and pediatrics.
Dr. Stukus has devoted his career to communicating evidence-based medicine and best clinical practice to colleagues, medical professionals of all backgrounds, patients, and the general public. In addition to providing clinical care for children with all types of allergic conditions, he participates in clinical research, quality improvement, patient advocacy, and medical education.