Although the terms “food allergy” and “food intolerance” are often used interchangeably, they’re actually quite different. Let’s see how.
A food allergy is an abnormal reaction of the immune system to a particular food. Symptoms appear quickly, sometimes within seconds or minutes. In the sensitization stage, the immune system encounters an allergen for the first time. Recognizing it as a potentially harmful foreign invader, the body produces antibodies. When the antibodies re-encounter the allergen in the reaction stage, they trigger cells to release inflammatory mediators such as histamine. As most food allergies are modulated by immunoglobulin-E (IgE) antibodies, one way to test for allergies is by measuring levels of specific IgE antibodies in the blood.
Allergy symptoms can be mild (an itchy nose or throat) or severe (nausea, vomiting, a drop in blood pressure, and difficulty breathing). Anaphylaxis refers to a serious and potentially life-threatening allergic reaction. Individuals with known allergies often carry an injectable syringe of epinephrine (adrenaline) commonly known as an EpiPen. Epinephrine can help combat these dangerous symptoms by decreasing swelling, constricting blood vessels to raise blood pressure, and relaxing lung muscles to aid breathing.
Ninety percent of food allergies are caused by eight foods: wheat, soy, milk, eggs, fish, shellfish, peanuts, and tree nuts. Pre-packaged foods that contain these allergens must be labeled by law.
Food intolerances can be caused by a variety of factors such as an enzyme deficiency. Lactose intolerant individuals don’t have enough of the lactase enzyme, which is needed to break lactose down into its component parts glucose and galactose. Lactose reaches the colon intact and is fermented by gut bacteria, leading to unpleasant symptoms such as bloating, gas, and diarrhea. Another example is histamine intolerance. Histamine builds up in the body when there are low levels of an enzyme called diamine oxidase (DAO). As mentioned previously, histamine plays a role in allergic reactions by acting as an inflammatory mediator (e.g. causing symptoms such as sneezing, itching, and eye watering that are meant to help you get the offending substance out of your body). Too much histamine can cause symptoms that mimic an allergic reaction. However, histamine intolerance is not an allergy in and of itself because it is not driven by an antibody reaction.
Unlike allergies, there is no blood test for food intolerances. Many food intolerance symptoms mimic indigestion, which may also be caused by stress, gut microbiome alterations, or poor food timing (e.g. eating a large meal late at night). Pay attention to your body and practice mindful eating to determine which foods and eating patterns make you feel best. A registered dietitian nutritionist can help you with a formal elimination diet to identify your triggers and re-introduce foods safely.