Allergy vs. Intolerance – What’s the difference?

So many people use these two words very loosely, but there is a fundamental difference between an allergy and an intolerance. So here’s what you need to know about them.

Food Allergies:

Food allergies can create a specific immediate antigen-antibody response. This means that certain food molecules are perceived by the body to be invaders and the body responds by producing antibodies (also known as immunoglobulins) to fight the intruders.

In the case of allergies, these antibodies are IgE antibodies that stimulate certain cells to release histamine, an inflammatory compound. In some cases, an allergic reaction can be life-threatening, like the anaphylactic choking reaction to eating peanuts in people allergic to peanuts.

Other food allergy symptoms can include swelling of the eyes and lips. Technically speaking, it is possible to have an allergy to any food. But the most common allergens include milk, gluten, wheat, nuts, eggs, mustard, sesame, soya and shellfish.

If you have a food allergy, you tend to know about it! A blood test will tell you for sure: a food allergy will show up as IgE markers.

Food Intolerances:

Food intolerances are far more common than food allergies, affecting as many as 20% of adults. Although they aren’t life-threatening, food intolerances can impact your quality of life in a big way.

The gold standard for diagnosing food intolerances is a guided exclusion diet, followed by a controlled reintroduction. Despite the many marketing claims out there, there is no valid test for a food intolerance (with lactose being the exception). Some of the common invalid tests to watch out for include IgG tests, hair analysis and muscle analysis.

The most common IgG test involves exposing a sample of your body to different foods and measuring the resulting IgG antibody. The test claims this is the marker of “intolerance”. But it’s not.

Unlike IgE, which are valid for diagnosing food allergies, most of us will actually develop IgG antibodies to food during our lifetime, despite not getting symptoms – this can be explained by the fact that IgG is actually an indicator of repeated exposure, not intolerance.

Some of the most common reported food intolerances are caused by lactose (milk sugars), wheat and gluten.


Lactose is a unique carbohydrate only found in milk from mammals. Lactose is made up to two sugars – glucose and galactose. In order for lactose to be absorbed from the intestine into the bloodstream it needs to be broken down into the two sugars by an enzyme called lactase, which is found in the lining of the small intestine.

Many adults don’t make enough lactase and therefore the lactose isn’t absorbed properly.


Wheat is often the first thing to be excluded when people suspect a food intolerance. Wheat is made up of components including gluten, wheatgerm agglutinin, amylase trypsin inhibitors and fructans, that may trigger people’s symptoms. So basically, a reaction to wheat might not always be a reaction to gluten.


Gluten is a family of proteins found in grains like wheat, rye, spelt and barley. There are many people who do not test positive for celiac disease, but still react negatively to gluten. This condition is called non-celiac gluten sensitivity.

However, a damaged microbiome and permeable intestinal barrier can allow pathogens and other toxins to enter the bloodstream. This can create an inflammatory reaction, which may be mistaken for a food intolerance response.

In some cases, the response might even not be inflammatory, it might just be a response to your gut’s inability to break down the compounds in certain foods!

Luckily, we don’t really have to get caught up in the details because we know that the best way to deal with these issues (other than celiac and allergies) is to heal a damaged gut lining and rebuild your gut microbiome!

Coeliac disease:

While we’re here, I thought it best to discuss coeliac disease, also known as Celiac disease. CD is a serious autoimmune disease. When people with CD eat gluten their body mounts an immune response that attacks the small intestine. These attacks lead to damage on the villi, small fingerlike projections that line the small intestine, that promote nutrient absorption. When the villi get damaged, nutrients cannot be absorbed properly into the body.

For most people, the best way to test for celiac disease is with the Tissue Transglutaminase IgA antibody, plus an IgA antibody blood test. This is known as a tTG-IgA test.

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