What’s the Difference Between a Food Allergy, a Food Sensitivity and a Food Intolerance?

Many of my clients with IBS, SIBO or IBD present with symptoms related to the foods they are eating.  It can be confusing to sort out whether the symptom is related to a food allergy, a food sensitivity or a food intolerance. 

It’s not always obvious because many of the symptoms can be the same.  You can have digestive discomfort with any of these conditions.

So how can you tell if your symptoms are from a food allergy, a food sensitivity or a food intolerance?  It takes detective work on behalf of both my clients and myself.  I tell my clients that if they are diligent in tracking their food in their food journal, we have a better chance to uncover the true cause of their symptoms.

So what are we looking for?  Below is an overview of each condition, the symptoms and how they are diagnosed.

Food Allergies – Involves the Immune System

Part of the reason for the confusion surrounding food allergies is that the term “food allergy” is used widely to refer to both a food allergy and a food sensitivity but it’s an important distinction.

A true food allergy is a reaction mediated by your immune system in response to an allergen.  Think of the immune system as a company with an organization chart that has several departments in charge of different functions.  One of those departments is the IgE branch and it governs allergies.

An allergen is perceived as an “invader” and the immune system mounts an attack by releasing inflammatory biochemicals that can cause a crazy set of symptoms.  You may recognize some of these symptoms as typical of allergies such as hives and sneezing but food allergies can cause one or more symptoms across the entire body.  The symptoms usually present fairly quickly (within minutes) after eating the allergenic food.  In some cases, a food allergy can be life threatening.

Food Allergy Symptoms

Runny nose

Throat tightening

Eczema, rashes & hives

Diarrhea, constipation, nausea, vomiting, bloating, acid reflux

Migraines & headaches


Brain fog

Frequent urination

Muscle aches


When a client presents with one or more allergic symptoms that occur soon after eating, I may suspect a food allergy.

How Are Food Allergies Diagnosed?

Allergists typically use skin prick/scratch tests or IgE blood tests to diagnose food allergies. Allergy tests can produce false positives so an allergist will also take into account whether you have any reactions to the foods that resulted in a positive result. 

What Are the Most Common Food Allergens?

The most common food allergens include:



Peanuts & Tree Nuts



Fish & Shellfish


Food Sensitivities

Food sensitivities can also present with similar symptoms as food allergies but they are not life threatening.  Food sensitivities involve different “departments” of the immune system including IgG, white blood cells and other molecules.  Symptoms can appear within a few hours or a few days. 

Food Sensitivity Symptoms – Another Type of Immune Reaction

Eczema & rashes

Diarrhea, constipation, nausea, vomiting, bloating, acid reflux

Migraines & headaches


Brain fog

Joint pain

How Are Food Sensitivities Diagnosed?

There are a plethora of food sensitivity tests on the market including those that measure IgG antibodies.  One of the biggest issues with IgG food sensitivity tests is that they are not reliable since healthy individuals produce IgG antibodies to foods. The presence of IgG antibodies doesn’t necessarily mean you have a food sensitivity.  A positive result may occur because you have eaten that particular food. 

True story: A client visited three different doctors and each had ordered a different food sensitivity test.  They all showed sensitivities to different foods.  There was not one common positive result among them. 

The only way to confirm a food that has tested positive on a food sensitivity test is to eliminate it for a period of time and then reintroduce it.   If your symptoms resolved when the food was eliminated and then reappeared when reintroduced then you confirmed the food sensitivity.  You may even be able to eat the reactive food again after it’s been eliminated for a longer period of time.

What is a Food Intolerance?

Unlike food allergies and food sensitivities that involve the immune system, a food intolerance involves the digestive system.  Food may be difficult to digest due to lack of enzymes or the biochemicals necessary to digest food.

Symptoms of Food Intolerances

Diarrhea, constipation, nausea, vomiting, bloating, acid reflux

Migraines & headaches

Brain fog

Joint pain


What Are Common Food Intolerances?

  • Lactose intolerance – The ability to digest dairy is limited due to limited production of the enzyme lactase, which digests lactose.  Approximately 65% of the world’s population has some degree of lactose intolerance. 
  • FODMAPS – These are poorly absorbed carbohydrates (including lactose), which can be found in numerous foods including some fruits, vegetables, grains, nuts, sweeteners and legumes.  Many of those with IBS and SIBO have issues digesting high-FODMAP foods.
  • Histamine intolerance – Histamine is a biochemical naturally present in the body and in food.  High histamine foods include fermented foods, cured meats, aged cheese, nuts, and citrus.  Histamine levels in our body can increase from eating high histamine foods, taking certain medications and by having a digestive condition like SIBO.  When the body lacks the DAO enzyme in amounts needed to degrade and clear histamine from the body this results in a build-up of histamine levels, which can cause a reaction.

How Food Intolerances Are Diagnosed

Some food intolerances can be diagnosed by a breath test.  I offer lactose, fructose and sucrose intolerance breath tests through Aerodiagnostics. 

Other intolerances are diagnosed by using a well-designed elimination diet. This is considered to be the gold standard in diagnosing a food intolerance or sensitivity.  Essentially, you eliminate suspect foods for a period of time and then reintroduce them to determine if it causes symptoms.  For severe symptoms of lactose, fructose or sucrose intolerance, you may want to consider the breath tests.

Where to Start

If you suspect you have a food allergy, a food sensitivity or a food intolerance, where do you even begin? 

1.     Start by keeping a food journal. 

2.     Track what you are eating, note the symptoms and when they first begin.  

3.     Sharing that data with a doctor and/or nutritionist will help determine the appropriate next steps and how to get relief ASAP.

Ready to figure out which foods are causing your symptoms and most importantly why?

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