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  • Marie Belzile-Davidson, MS, Dietetic Intern

Food Allergies vs. Sensitivities vs. Intolerances

Ever wonder what the differences are between a food allergy, a food sensitivity, and a food intolerance? All three of these are food reactions, they all cause physical symptoms, and they have similar names. Confusing, right?

We are going to break these down one by one because they are quite unique. Knowing the difference between an allergy, sensitivity, and intolerance can help you best navigate your health care if you suspect you have one or all three of these food reactions.

Food Allergy

A food allergy is an adverse reaction due to exposure to a specific food (or a component within a food) that triggers an immune response. It can be IgE-mediated or non-IgE-mediated. Non-IgE mediated allergies are a newer discovery in the world of food allergies. This immune response typically causes sudden symptoms. These symptoms can vary from one person to another and at best are unpleasant but can be life-threatening. Some include rashes, facial swelling, fainting, and difficulty breathing. It does not take a large amount of the allergen for the body to unleash its immune response. In fact, extremely sensitive individuals can have an allergic reaction to just trace amounts of the specific food or food component.

So how common are food allergies? Based on a study in 2017, about 4% of American adults have a true food allergy. Food allergies were once thought to only develop in early childhood. While food allergies still mainly affect children, we now know that food allergies can show up at any point in our lives. There is currently a large increase in the number of adult and elderly people diagnosed with food allergies, especially in Western countries. The reason(s) why is not well known yet but there is evidence suggesting that lifestyle and environmental changes may play a role.

Many foods can trigger allergic reactions in individuals. In fact, there are over 160 foods that are known to be allergens to some individuals. However, the list of common food allergens is quite small. These common allergens can vary from country to country so let's focus on the United States. You may have heard of the "Big 8" (soon to be the "Big 9" in January of 2023). These are the top sources of food allergies in our country and require special handling in food processing and labeling on packaged foods. They are milk, eggs, soy, wheat, peanuts, tree nuts, fish, shellfish and crustaceans, and the newest addition - sesame.

When it comes to diagnosing a food allergy, there are several tests and tools an allergist may use. If you have read our blogs before, you know that nutrition is highly individualized because we are all so unique. That means, one health care approach for one person is not necessarily the best option for another. Allergists may use prick tests, IgE blood tests, clinical history, elimination diets, and/or oral food challenges to diagnose a food allergy.

Food allergies can follow someone through their entire life or can sometimes go away. The general approach to treating a food allergy is to completely eliminate that food from the individual's diet. There are innovative therapies and immunotherapies that may help individuals with food allergies lessen the severity of their allergic response. This is definitely an area to keep an eye on for up-and-coming research and findings. However, there is no "cure" for a food allergy at this time. Adrenaline shots (commonly known as EpiPens) are an emergency treatment that can help prevent a fatal outcome from a severe reaction if someone with a food allergy accidentally consumes an allergen.

Food Sensitivity

A food sensitivity is similar to an allergy in the sense that it is also immune-mediated. Food allergies and sensitivities also share some similar symptoms. However, with sensitivities, the onset of symptoms is typically delayed, the symptoms may last longer, and there is no IgE antibody response. The types and severity of symptoms felt from a food sensitivity can also vary based on how much of the food (or food component) you were exposed to and how frequently you were exposed to it. Food sensitivity symptoms can be disruptive and unpleasant but are typically not life-threatening. Some symptoms include stomach pain, rashes, brain fog, and joint pain.

It is important to note that at this time, a food sensitivity is not an official medical diagnosis (a food allergy is) and there is no officially agreed upon medical definition of a food sensitivity. What? So are food sensitivities even real then? Sometimes the term "food sensitivity" is used interchangeably with "food intolerance" but as you will read about in a minute, food intolerances do not involve the immune system, food sensitivities do. Here's the simple answer for now (remember, science is always evolving as new research is conducted): people can and do experience sensitivities to foods in ways that are not allergic reactions nor intolerances. There are approaches within functional nutrition to address the root cause of these sensitivities to help lessen or alleviate the symptoms. But! We have much left to research and learn on this topic and there is no absolute way to know whether or not you have a food sensitivity.

Hold on, if there is no medical consensus on how to define a food sensitivity and it is not an official medical diagnosis, do these at-home food sensitivity tests we see all over social media and television ads actually work? These at-home tests are quite unreliable and there is no evidence to support that dietary changes should be made based on their results. These tests typically look for the presence of IgG antibodies from your immune system but that is just one antibody - there are many more that can be involved in a reaction to a food sensitivity. Also, the presence of IgG antibodies is not specific to food sensitivities.

There are some tests available to licensed health care providers (like Registered Dietitians) that are much more specific and look at many more components than those other at-home test kits. These tests can tip health care providers off that some food(s) may be aggravating your body and immune system in some way. However, food sensitivities are likely a symptom of some other underlying issue like gut inflammation or intestinal permeability (leaky gut).

How are food sensitivities treated? They can be addressed by looking for the root cause and treating that through diet and lifestyle changes. For example, maybe you are experiencing leaky gut (more on that here). This means food particles that you typically would have no immune response to can travel outside of your intestines (where they do not belong) and trigger your immune system as a potential "invader." This sensitivity may be lessened or resolved by addressing and correcting the underlying issue of leaky gut.

Food Intolerance

A food intolerance, unlike an allergy or sensitivity, is not immune-mediated. It can be occur for a variety of reasons. One is enzymatic insufficiency. This is when your body does not have enough of or completely lacks the enzyme(s) needed to break down a particular food or a particular part of food. A food intolerance can also be due to some other non-specific gastrointestinal functions.

Let's take lactose intolerance and intolerance to FODMAPs as examples: lactose is a sugar found within milk (and therefore other dairy products like butter, cheese, yogurt, etc.). Lactose is broken down by the enzyme lactase, which is made by your small intestine. Normally, lactose is broken down/digested in the small intestine. If your small intestine does not make enough or any lactase, then lactose travels intact to the large intestine, where your gut bacteria have a field day breaking it down. This is where those pesky lactose intolerance symptoms of gas, bloating, and diarrhea come from. Let's look at FODMAPs: these are specific types of fermentable carbohydrates that can also cause gas, bloating, and diarrhea. If someone is intolerant to FODMAPs it may not necessarily be because they are lacking specific enzymes but rather, could be due to some dysbiosis in their gut microbiota and/or another gastrointestinal function. To summarize, we feel discomfort from foods we may have intolerances to because our digestive system cannot properly break them down for one reason or another.

Food intolerances are also much more common than allergies, affecting about 15-20% of the population. The symptoms someone experiences from a food intolerance can vary from food to food and person to person. It can also depend on how much of a certain food someone has eaten. Going back to our lactose intolerance example - someone with this intolerance may be able to eat a small piece of cheese and experience mild or no symptoms. If they ate a cheese-loaded lasagna, on the other hand, that may be a different story.

Since food intolerance symptoms can vary from person to person, can be based on the amount of food eaten, can be caused by countless foods, and can be due to a variety of mechanisms, diagnosing a food intolerance is not straightforward. There are some tests to evaluate specific intolerances, such as fructose and lactose intolerance, but those are just two of many potential food intolerances. Identifying a food intolerance usually relies on a detailed medical history, keeping track of symptom patterns with specific foods, and potentially eliminating the suspected culprit(s) for a period of time and then reintroducing them under the guidance of a licensed health care provider.

Because food interlaces vary so widely, the treatment approach will look different from person to person, based on what food is involved and the mechanism responsible for the intolerance.

Putting It All Together

While food allergies are a little more straightforward, the same cannot be said for food sensitivities and intolerances. The truth is, all of these adverse food reactions are nuanced in their own ways. The major takeaways we hope you have gathered today are:

  • Adverse food reactions can be quite serious and difficult to diagnose (do not waste your money on those at-home IgG food sensitivity kits!) so it is important to seek out a licensed health care provider to help you navigate the situation in a way that is best for you.

  • The answer to treating food sensitivities and food intolerances is not simply avoiding those foods for the rest of your life! These reactions may be linked to other underlying conditions that should be addressed. On top of that, unnecessarily eliminating foods long-term can increase your risk of nutrient deficiencies, which can cause a whole slew of health complications.


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