A nutritionist explains food allergies and intolerances
The two are often confused, but while allergies and intolerance can both make you feel bad, effective treatment relies on you knowing the difference.
My clients often come to me with symptoms they associate with the foods they're eating. Hives, digestive discomfort, post-nasal drip---these can all raise concerns about possible food allergies or intolerances. While people may use the terms interchangeably, they are pretty different, and it's vital to distinguish the two to deal with any symptoms you may see from your diet. Here, we look at the key differences and explore strategies to manage them effectively.
Food allergies: immune system activation
A food allergy occurs when the body identifies a particular food as harmful, triggering an adverse immune system reaction. This response is most often mediated by Immunoglobulin E (IgE) antibodies, which attach to immune cells such as mast cells and basophils, concentrated in areas like the skin, respiratory system, and gastrointestinal tract. When the body encounters the allergen again, these IgE-primed cells release inflammatory chemicals such as histamine, which contributes to the symptoms of an allergic reaction such as hives, itching, and swelling. Reactions can vary widely; in some cases, they may be mild and manageable with antihistamines, while in others, symptoms can escalate if untreated. In severe cases, anaphylaxis can occur, requiring immediate intervention with an epinephrine injection followed by medical care, as it can lead to shock, throat swelling, and potentially fatal breathing obstruction.
The eight most common food allergens in the United States are fish, shellfish, milk, eggs, soy, wheat, tree nuts, and peanuts. The FDA requires food manufacturers to identify these as ingredients under the Food Allergen Labeling and Consumer Protection Act of 2004 (FALCPA). Sesame was recently added as a ninth.
Food intolerances: digestive or enzyme-related issues
Food intolerances, unlike allergies, don't involve the immune system. Instead, they usually stem from the body's inability to properly break down certain foods due to enzyme deficiencies or digestive issues. Symptoms of food intolerances are generally milder than allergic reactions and primarily manifest as digestive discomfort (e.g., bloating, gas, diarrhea, abdominal pain, nausea), although they can also include headaches, congestion, fatigue, and skin issues.
One common example of an intolerance is lactose malabsorption. Approximately 68% of the world's population produces a lower level of the enzyme lactase, which breaks down lactose (the sugar found in milk) into its component sugars, glucose and galactose. Gut bacteria ferment this undigested lactose in the small intestine, producing gas, bloating, and diarrhea. (Lactose intolerance describes when fermenting occurs in the colon instead of the intestines, though the effect is similar.)
Histamine intolerance is another example, where the body can't properly break down histamine due to reduced activity of the enzyme diamine oxidase (DAO). Histamine is found naturally in foods like aged cheeses, cured meats, and fermented vegetables. Certain foods, such as tomatoes, chocolate, avocados, spinach, and eggplant, also trigger the body to release histamine. For histamine-intolerant people, eating too many of these foods may lead to symptoms both within and beyond the digestive system, including headaches, skin rashes, and congestion.
Key differences between food allergies and intolerances
Although some characteristics of food allergies and intolerances may overlap, there are essential differences in the mechanisms behind these reactions and how they affect the body. Understanding these distinctions is important for diagnosis and treatment.
Immune system vs. digestive issues
Food allergies involve the immune system's response to specific proteins in food, whereas intolerances are caused by digestive issues, enzyme deficiencies, or chemical sensitivities.
Severity of reactions
Allergic reactions can range from mild to life-threatening, with some allergies resulting in anaphylaxis, which can be fatal if not treated immediately. This potential for severe reactions means that food allergies require strictly avoiding the allergen and emergency preparedness, including access to an epinephrine auto-injector (EpiPen). Food intolerances, by contrast, typically lead to discomfort rather than danger.
Time of onset
Allergic reactions usually occur within minutes to an hour after consuming the allergen. Intolerance symptoms, however, may take hours or even days to show up, which can make identifying trigger foods more challenging.
Diagnosis and medical evaluation
Proper diagnosis is essential to distinguish between food allergies and intolerances, as management of each requires a different approach.
Diagnosing food allergies
Doctors commonly use skin prick tests and blood tests to diagnose allergies, with skin prick tests generally considered the first-line approach. In a skin prick test, a small amount of the suspected allergen is applied to the skin, which is then pricked to introduce it beneath the surface. If a reaction occurs, it suggests a potential allergy. Blood tests measure levels of IgE antibodies specific to particular allergens. However, they have been known to give false positives over half the time and are not recommended by organizations like the American Academy of Allergy, Asthma & Immunology, though they may be used to test a suspected or known allergen. In some cases, an oral food challenge may be used, where the individual consumes small amounts of the suspected allergen under medical supervision to observe any reaction. While highly accurate, this test is riskier and requires close monitoring.
Diagnosing food intolerances
The gold standard diagnostic test for food intolerances is often an elimination diet, where you remove common trigger foods from your diet and reintroduce them one at a time. If done correctly, this test isolates the effect of each food on the body. For lactose intolerance, doctors may use a hydrogen breath test; when undigested lactose ferments in the gut, it elevates hydrogen levels. Histamine intolerance can be more challenging to diagnose as no standardized tests exist. However, a trial of a low-histamine diet or DAO enzyme supplement will provide clues. For multiple intolerances, you may consider functional lab tests like the Mediator Release Test (MRT), which measures the release of non-IgE chemical mediators, such as histamine, prostaglandins, and cytokines, from white blood cells when exposed to specific foods or food chemicals. However, more research is needed to validate its effectiveness.
Managing food allergies vs. intolerances
You can manage both food allergies and intolerances effectively with diet and lifestyle:
Managing food allergies
People with food allergies must avoid their allergens altogether. For example, someone with a peanut allergy must restrict all forms of peanuts, such as peanut butter and peanut oil. They must also be careful about cross-contamination risks. Reading food labels, being vocal at restaurants, and educating family, friends, and colleagues about the allergy can all help keep them safe. While some people, particularly children, may naturally outgrow allergies to foods like milk, eggs, and soy, factors such as the severity of the allergy, how early it appeared, and how it's managed can influence whether it persists or resolves. The immune system may gradually build tolerance through controlled exposure, and emerging therapies aim to reduce sensitivity. However, anyone with a history of severe allergic reactions should always carry an EpiPen.
Managing food intolerances
People with food intolerances can sometimes tolerate small amounts of their trigger foods. They can also use supplements, such as lactase for lactose intolerance. Being mindful of portion sizes and selective with trigger foods is also helpful. For example, a histamine-intolerant person may be able to have a little bit of avocado on toast at breakfast but have more difficulty if they add an omelet with spinach and tomato.
Practical tips for managing food reactions in daily life
Read labels thoroughly
Allergens may be hidden or have alternative names. For example, wheat could be labeled as gluten or barley malt, and people with lactose intolerance should watch for lactose-containing foods like milk, cream, yogurt, and certain processed foods that use lactose as an ingredient. Becoming familiar with alternative names for trigger foods and getting in the habit of reading food labels can be helpful.
Educate friends and family
Inform people you frequently share meals with about your needs, such as avoiding certain ingredients or using separate utensils to provide cross-contamination. It will also likely increase support. Providing alternate recipe ideas or hosting a safe dinner are fun ways to make your restriction known and understood.
Carry safe snacks or alternatives
Carrying safe alternatives to social gatherings and events can decrease stress and risk. Options that many people can tolerate include fresh fruit like apples or bananas, plain rice cakes, seed-based snack bars, gluten-free crackers, and individual packets of nut or seed butters. These snacks are transportable and keep well, making them easy to stash in your backpack or purse.
Communicate with restaurant staff
Informing restaurant staff about dietary needs will significantly reduce the chances of an adverse reaction. Clearly explain any allergies or intolerances to the server and ask questions about food preparation, as cross-contamination can occur in kitchens. Calling ahead and speaking with the manager or chef can also be helpful.
Keep a food journal
A detailed diet journal is an excellent tool for identifying trigger foods. Keep track of what you ate, the date and time you ate it, and all symptoms, including when they appeared. Include details such as preparation methods and portion sizes. Tracking patterns over time helps highlight sensitivity patterns that may not be obvious with isolated meals. A food journal can also provide valuable insights to healthcare providers as they guide you in effective management strategies.
Conclusion
Food allergies can cause severe, life-threatening reactions and require strict avoidance of the allergen. Intolerances, on the other hand, can be handled more flexibly with strategies like portion control and digestive support. Recognizing the critical distinctions between food allergies and intolerances allows people to make informed choices that keep them safe and symptom-free. With the proper knowledge, it's possible to enjoy food without worrying about unexpected reactions.
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