Food Allergies vs. Food Intolerances: Know the Facts

Food Allergies vs. Food Intolerances: Know the Facts

By Rebecca Ditkoff, MPH RD CDN

Let’s clear something up—food allergies and food intolerances are not the same thing. These terms are often used interchangeably, but it’s important to note that there are several differences between the two. Food allergies involve the immune system and may be life-threatening. Meanwhile, food intolerances involve the digestive system, and although debilitating in some cases, are not life-threatening.

Food allergy: A food allergy is an immune system response that occurs when the body believes a particular food is a harmful substance. In response, immunoglobulin E (IgE) antibodies are released, along with chemicals such as histamine, which leads to an allergic reaction. 

Food intolerance: A food intolerance is defined as an undesirable reaction to a food that is not immune-mediated.

Defining the differences

Common food sources: Top 8 Allergens: milk, eggs, wheat, fish, shellfish, tree nuts, peanuts, soy.

Cause: Caused by an immune response to a protein found in the allergen.

Prevalence: Occurs in approximately 1-3% of adults and less than 10% of children (Turnbull J.L., Adams H.N., Gorard D.A. Review article: The diagnosis and management of food allergy and food intolerances. Aliment. Pharmacol. Ther. 2015;41:3–25. doi: 10.1111/apt.12984)

Symptoms: Symptoms are immediate and can present themselves after just a small exposure to an allergen. Symptoms may include: hives; eczema; itchy or tingling mouth; swelling of the lips, tongue, face or throat; shortness of breath; vomiting, diarrhea, or abdominal pain; weak pulse/drop in blood pressure, and in severe cases anaphylaxis.

Common food sources: Sugar compounds such as monosaccharides or disaccharides (i.e fructose, sucrose, lactose and maltose); FODMAPs (an acronym for fermentable carbohydrates which are often a culprit for digestive issues in those with IBS); Caffeine; Chemicals such as Sulfites (found in wine, aged cheeses and dried fruits) and Salicylates (found in certain foods such as some fruits, vegetables, and nuts), and Histamine (found in fermented foods and beverages).

Cause: Not immune-mediated. Occurs for various (i.e enzyme deficiency, irritable bowel syndrome) and sometimes unknown reasons.

Prevalence: Occurs in 20% of the population.

Symptoms: Symptoms generally come on gradually (can take up to 48 hours) and may only happen if you eat certain types of food or eat past your tolerance threshold. Symptoms may include: abdominal pain, bloating, gas, nausea, vomiting, diarrhea, skin rashes, migraine, cough, and fatigue.

Diagnosing Allergies

People that have symptoms consistent with food allergies should always be evaluated by a qualified medical professional, such as a board-certified allergist. Skin prick tests remain the "gold standard" for detection of allergen-specific IgE, in addition to testing serum-specific IgE levels. However, these tests only correlate with the likelihood of a clinically relevant reaction to food and do not correlate with the intensity of the reaction.

Diagnosing Food Intolerances

A food intolerance is sometimes a bit more challenging to pinpoint since you may be able to eat small amounts of a food you’re intolerant to without any issues, whereas with a food allergy, consuming only a small amount can trigger an allergic response. Additionally, aside from enzyme-related intolerances (such as lactose, fructose, sucrose, and maltose), which can be measured using a breath test or by a disaccharidase assay via a small bowel biopsy, intolerances do not have a single diagnostic test to confirm a diagnosis. Although alternative health care providers and online marketers often try to sell “IgG food sensitivity tests”, these are not accurate or science-based and therefore are a waste of money and time. IgG is a memory antibody, which means that it just demonstrates a memory of encountering a food component. This leads to a frequency of false positives and confusion for the patient, potentially affecting their relationship with food and leading to unnecessary restrictions.

The Role of Food Diaries and Elimination Diets

Therefore, without valid testing, the best way to identify food intolerances is to use a trial and error approach. Keeping a detailed food and symptom diary is a great place to start. This includes writing down what you eat for every meal (including all ingredients and portions) and then listing any symptoms that occur, using the Likert scale of 1-10 for intensity. Next, a strategic short-term removal of food components followed by re-introduction to assess symptom response may be required. It is important not to self-diagnose as this can lead to unnecessary restrictions. Therefore, this process is best done with the help of a Registered Dietitian who specializes in elimination diets and can help ensure you don’t over-restrict your diet, while maintaining adequate nutrition.

What about gluten?

Gluten is the protein found in wheat, rye, and barley. As noted above, wheat is classified as one of the top 8 allergens. It gets a bit confusing when it comes to Celiac disease, since this disorder is actually different from a wheat allergy, which is an IgE immune-mediated response. Instead, Celiac disease is an autoimmune disorder in which the body attacks itself (specifically the small intestine) when gluten is ingested. Therefore, it is not technically classified as an allergy even though it ends up being managed like one since even trace amounts can damage the small intestine and lead to digestive symptoms. Gastroenterologists can diagnose celiac disease with a blood test and confirm the diagnosis with a biopsy of the small intestine.

Non-celiac gluten sensitivity (NCGS) is a similar condition, though a somewhat controversial one given its causes are not fully understood. NCGS is considered an intolerance and lacks a single test for diagnosis. Instead, it is identified by first ruling out a wheat allergy and celiac disease.


Find a substitution. If the food you’re allergic to or can’t tolerate provides a vital source of nutrients, it is important you find an adequate replacement. For example, when cutting out gluten, you may not be getting adequate B vitamins. Therefore, it is important to substitute for gluten-free grains that are a good source of B vitamins, including millet (one of the main ingredients in Hilary’s veggie burgers), buckwheat, and sorghum.

Adjust serving sizes. This is not possible for allergies since a small amount can cause a reaction, but for those with food intolerances, you can sometimes still enjoy your favorite foods by reducing the amount. For example, if you have lactose intolerance, you may find you can still tolerate a little bit of milk in coffee.

Using enzyme tablets or drops. Although these don’t always work for everyone, tablets or drops containing replacement enzymes may help with difficult digestion. Over-the-counter examples include Lactaid and Fructaid, while you can get Sucraid with a prescription. All of these can be taken just before a meal or a snack.


Whether you or someone you know has food allergies or intolerances, it is important to note that with proper management, they can be well controlled, in a way that is safe and nourishing for the body.

Hilary’s products are proud to be free of the 12 top allergens as well as many of the common causes of food intolerances. You can learn more about Hilary's commitment to create 'free-from' food options here



Rebecca Ditkoff, MPH, RDN, CDN  is a Registered Dietitian specializing in digestive health and disordered eating. Her non-diet approach to nutrition is rooted in the theories of Intuitive Eating and Health at Every Size (HAES) in which she emphasizes self-care over rigid diet rules and restriction . She is the founder of  Nutrition by RD, a brand dedicated to helping people improve their relationship with food and their bodies. Rebecca also runs a virtual nutrition counseling practice from New York, NY where she works with clients one-on-one providing personalized nutrition counseling. She has been featured in a number of publications including: Women’s Health, Prevention, Forbes, Real Simple, The Huffington Post, and many more. Rebecca enjoys traveling, live music, daily trips to the dog park with her Chihuahua-mix named Winnie, and experimenting with new recipes in the kitchen.