Allergy vs. Intolerance

Dietitians are detective by nature.  We examine health problems in the context of food and we determine appropriate dietary changes.  Sometimes, individuals don't react to medical interventions but respond to dietary changes, which is why our job can be so exciting.  Wasn't it Hippocrates that said "Let food be thy medicine and medicine be thy food?"  But it can't always be that clear, which is why determining if a gluten-free diet is right for you might be difficult.  You might be gluten-sensitive, which means your body reacts to gluten in a negative way, but you are not allergic to gluten.  So what is the difference between an allergy and an intolerance?

A food allergy is an exaggerated response by your body's immune system to a food you have consumed. Normally, when your body detects a foreign invader, such as a virus, bacteria, and even an specific type of food, it signals your immune system (white blood cells, chemicals, proteins, and enzymes) to defend against the invader.  Your white blood cells produce what are called antibodies, which attach to the invaders (referred to as antigens) so that they can be destroyed.  But when you have a food allergy this does not happen.  When you consume the dangerous food item, you experience an immediate-onset allergy.  First, your body produces IgE, when is a food-specific antibody called immunoglobulin E.  This is a type of protein.  One side of the IgE antibody senses the food invader and binds to it in an attempt to destroy the particle.  The other side of the IgE antibody attaches to what is called a mast cell, which is an immune cell loaded with histamine.  Mast cells are present in all body tissues, but most are found in your nose, throat, lungs, skin and GI tract.  Therefore, the next time you eat the dangerous food, the IgE antibodies instantly attach themselves to that food, which causes a histamine reaction and other allergy-related chemicals to be released from the mast cell.  Examples of histamine reactions include hives, diarrhea, gastric symptoms, etc.  Sometimes reactions may be severe, such as anaphylaxis in which an individuals breathing can completely obstructed and they can die.  

You might think you have a food allergy when in fact you have food immune reactivity (FIR).  FIR is food intolerance, which is a delayed reaction to eating a certain food.  Examples of FIR include wheat, barley, rye, dairy products, tomato, potato, eggplant, peppers and soy products. The symptoms of FIR are at times similar to those you might experience with an allergic reaction, but the cause is not always immediately identified. Reactions are typically delayed by sometimes hours to days.  FIR does not involve IgE reactions, so histamines are not released and therefore prescribing an antihistamine would not be effective. In FIR, specifically gluten-sensitivity, the body may produce antibodies called antigliadin IgA antibody, anti-tissue transglutaminase antibody, and anti-endomysial antibody.  These antibodies do not trigger histamines, but they can cause chronic inflammation and can eventually lead to the complete flattening of the intestinal villi, which are finger-like projections in the intestines that absorb nutrients.  This then becomes Celiac Disease.  Long-term effects of FIR can include permanent organ damage, tissue damage, and a hyper-activated immune system which can result in inflammation.  

The only treatment for both FIR and a food allergy is complete elimination of the "food invader" from your diet.  If you have not been diagnosed with having a food allergy you might still be sensitive to a certain food.  When eliminating that food from your diet, you might experience an improvement in the way you feel.  Sometimes it's not always black and white, but let your food be your medicine and experiment!