Many parents worry that their child could have a serious reaction to something they eat. Can you recognize the symptoms of a food allergy? What’s the difference between an allergy and an intolerance? As with many health issues, the Internet is rife with conflicting information, and there are plenty of sites selling unproven tests and treatments. In this article, I answer the most common questions about food allergy, intolerance, and sensitivity to clear up the confusion and help you protect your loved ones.
What’s the difference between allergy, intolerance, and sensitivity?
A food allergy is an immune system response. It occurs when your body mistakenly identifies a food as harmful and, in its defense, triggers an allergic reaction that can range from mild to severe. The reaction is reproducible – meaning it happens every time the offending food is eaten – and fast, occurring within minutes to a few hours.
Food intolerance is a digestive system response. It happens when your body can’t properly digest something, often due to the lack of a needed enzyme. Food intolerance symptoms may occur many hours or even a couple of days after eating the food, and can be variable based on a number of factors. The most common example of food intolerance is lactose intolerance.
The symptoms of food sensitivity tend to be vague and variable. Reported symptoms of food sensitivity include headache, fatigue, brain fog, or pain. Food sensitivities often can’t be diagnosed with a lab test. As a result, they may be the target of unsupported, often expensive tests and treatments. It’s not that the issue doesn’t exist; rather, it’s an individual experience that is difficult to diagnose or prove.
The most common symptoms of a food allergy include tingling or itching in the mouth, hives, swelling of the face or sometimes elsewhere. There may also be abdominal pain, diarrhea, and vomiting.
In severe cases, anaphylaxis occurs. This is a severe allergic reaction that needs immediate medical attention. The symptoms of anaphylaxis include difficulty breathing, rapid heart rate, lightheadedness, a drop in blood pressure, loss of consciousness, and sometimes death. This is why people with severe allergies need to carry an autoinjector – a device that injects a dose of epinephrine, which halts the progression of anaphylaxis to give the paramedics time to arrive.
You can become allergic to any type of food – even foods that you’ve eaten many times throughout your life. However, food allergies often start in childhood and there are nine foods that cause the majority of allergic reactions: eggs, milk, peanuts, tree nuts, soy, wheat, fish, shellfish, and sesame. People often outgrow allergies to eggs and dairy, but allergy to peanuts, tree nuts, and shellfish are usually lifelong.
What Happens When You Have a Food Allergy?
The immune system is complex with many interconnected components. White blood cells circulate throughout the body and monitor for invaders. When a foreign molecule is encountered, the white cells make immunoglobulins (Ig) which bind to the threatening substance and mark it for destruction. Plasma cells are white blood cells that secrete IgE, the main immunoglobulin involved in an allergic reaction. If you’re allergic to peanuts, the IgE recognizes and binds to the peanut protein and signals other white cells (mast cells and basophils) to release a bunch of chemicals like histamine that cause the symptoms of an allergic reaction.
How is food allergy diagnosed?
There are two common tests: A blood test to measure IgE levels against specific foods, and a skin scratch test in which the allergist places a droplet containing the food protein on the skin and makes a small scratch. If IgE to that food is present, it will stimulate the release of histamine causing a welt to develop at the site of the scratch.
Intolerance is the inability to digest a food or group of foods, frequently due to lack of the enzyme needed to break that food down. The most common symptoms are stomach pain, bloating, gas, heartburn, and diarrhea. Unlike allergic reactions, the symptoms can occur days after eating the food and may be variable based on factors like how much of the food was ingested, and how the food was made.
Lactose intolerance is the most common example. If you develop gas, bloating, and diarrhea after eating dairy, you may not make the enzyme lactase, which breaks down lactose, the main sugar in milk. Some people can make low levels of lactase and can tolerate some dairy, but will have symptoms if they overdo it. Others can tolerate fermented dairy like yogurt and kefir. Lactose intolerance is treated by avoiding dairy or by taking a lactase supplement.
Food sensitivity is less well defined than intolerance, but may share similar symptoms. A number of substances found in foods have been implicated in food sensitivity including gluten, histamine, salicylates, glutamate, various food additives, and FODMAPs.
FODMAPs are fermentable short-chain carbohydrates that may play a role in irritable bowel syndrome. The list of high FODMAP foods is long and includes everything from milk and ice cream to beans, lentils, apples, pears, peaches, wheat products, and various vegetables such as asparagus and onions. Many FODMAP foods are healthy and a low FODMAP diet can be restrictive, not only impacting quality of life, but also potentially leading to nutritional deficiencies. It is meant to be a short-term diet done under the close supervision of a qualified dietitian with gradual reintroduction of food over time.
Gluten sensitivity is not the same thing as Celiac disease. Non-celiac gluten sensitivity (NCGS) has similar gut symptoms, but people also report fatigue, headache, brain fog, and numbness or joint pain. There are no tests to diagnose NCGS and the evidence supporting this as a real disorder is mixed. Unlike FODMAPS, many of the triggering foods are unhealthy and ultra-processed, so it’s difficult to tease out what’s really causing the symptoms. The bottom line here is, if you feel bad when you eat gluten-containing foods, then don’t eat them, but be sure to replace them with healthy whole plant-based food.
A warning about IgG tests
When it comes to food sensitivity, the wellness industry is full of people touting tests and treatments that are not backed by science. A good example is the wide availability of IgG tests claiming to diagnose food allergies. Recall that food allergies are mediated by IgE. IgG is the most common antibody found in the blood and its main job is to help the immune system fight off infection by bacteria and viruses. When your immune system is exposed to proteins from digested food, it may make IgG specific to that food, but that doesn’t mean you’re allergic to the food. In fact, higher levels of IgG to foods have been shown in studies to protect against an allergic reaction. Once you have IgG for a food, you will have that antibody for life. Interestingly, when people grow out of allergies, say to eggs, the IgE level will decline and disappear, but the IgG level will actually go up. So, don’t be fooled by someone claiming that they can diagnose hidden food allergies with an IgG test – It’s not only a waste of money, but you’re also wasting time and potentially delaying the diagnosis and treatment of the real cause of your symptoms.
To summarize: food allergies are an immune system reaction that occurs in the immediate period after eating the triggering food. It occurs every time you eat that food with the same or similar symptoms. Food intolerance occurs when you can’t digest a certain component of food – such as lactose in milk – because you lack the necessary enzymes. The symptoms are primarily GI discomfort, and they can vary and occur hours or days after eating the food. Food sensitivity may involve inconsistent, non-specific symptoms and don’t have a cause that can be diagnosed based on test results.
If you’re worried that your child may have had a reaction to something they ate, be sure to stop offering that food and talk to your pediatrician. Having to restrict common foods from the diet can be anxiety-provoking and can affect quality of life, so it’s important to get an accurate diagnosis whenever possible.