Saturday, February 27, 2016

"Was It Something I Ate?" Asthma and Food Allergies

Food allergies are on people’s minds and in the news. Along with other diseases such as allergic asthma, eczema (aka “atopic dermatitis”), and allergic rhinitis and conjunctivitis (aka “hay fever”), food allergies are common (affecting about 7% of children in the United States) and seem to be on the rise. What are food allergies and how can they relate to asthma? Answering these questions is the goal of this first of a three-part blog entry.
Part 1:
Just what are food allergies? Getting the terms straight.
Studies show that a lot more people think they have food allergies than actually do, but that’s not necessarily because people overcall problems. Rather, it has to do with how the term “food allergy” is defined by western medicine as opposed to its common usage.
In medical parlance, when something unpleasant or harmful happens to a person after eating a particular food, it is referred to as an “adverse food reaction” (AFR). AFR is a broad category, and true food allergy is but one subset of the big AFR group. That is, all food allergies are AFRs, but there are real AFRs that are not allergic reactions. In our more relaxed, common way of speaking, however, we often use the words “food allergy” when we are referring to any kind of AFR.

Here’s an analogy that might help. Consider the set of AFRs to be like the set of motor vehicles. This big group of motor vehicles includes cars, trucks, vans, motorcycles, and mopeds. Maybe it even includes construction vehicles like steamrollers or water craft like speed boats. Now imagine a subgroup of motor vehicles, say trucks. Clearly all trucks are motor vehicles (that is, they belong to that larger set). But there are also motor vehicles that are not trucks (for example, mopeds and steamrollers). So the large category of AFRs is like the large category of motor vehicles, and the subset of true food allergies is analogous to the subset of trucks. The problem arises when someone says “I have a truck” when what that person really meant was “I have a motor vehicle,” because in a colloquial way of speaking we are less rigorous with our terms. That’s why a lot of people report having a food allergy – what they are really saying is “I have an adverse food reaction," and only some of them have a true allergy according to the strict definition.

This is where the analogy above breaks down. Most people who have a motor vehicle can instantly tell whether it is a truck or not – just look at it and one can answer the question, “Is this motor vehicle in the truck family?” Most of us carry around some criteria for answering that question – a truck is the sort of motor vehicle that has at least four wheels, a truck bed, one of a few body shapes, etc.  But how does someone know if his or her AFR is in the family of true food allergies? What are the criteria for that? Turns out it’s not so easy (or impossible) to tell if an AFR is a true food allergy without considering the classic symptoms. And while we’re at it, what does food allergy have to do with asthma anyway?
What are the symptoms of a true food allergy?
After that overly long introduction, it’s time to get down to the real stuff. If food allergies are a subgroup of AFR, exactly what qualifies an AFR to be called accurately a true food allergy? How can we decide if a person is really allergic to a food?
True food allergies are reactions caused by part of the immune system responding to the presence of one or more particular foods taken into the body. These reactions typically occur within a few minutes to a few hours of ingestion of the trigger food(s). So right off the bat, if a person complains of a food allergy causing symptoms a week after he (one time) ate some particular food, we can tell him that he may have had an AFR, but he probably does not have a real allergy to that food
Almost all allergic reactions to a food somehow involve the skin or the moist linings of the body such as the mouth (those moist linings are referred to as “mucous membranes,” “mucosal surfaces,” or “mucosae” for short) with symptoms like itching, flushing, hives, or swelling. Since the food allergen causing the reaction is typically eaten, a lot of food allergic patients have nausea, vomiting, cramping abdominal pain, or diarrhea. When more severe, people may become lightheaded or even faint.
But this blog post wouldn’t be complete if it didn’t mention asthma. People, especially those with known asthma, who experience an allergic reaction to a food can rapidly develop shortness of breath, wheezing, cough, and chest tightness – the classic symptoms of asthma. So while respiratory infections, cold air, exercise, and airborne allergens are among the “most likely suspects” in an asthma attack, add food allergens to the list in some people.