The difference between a food allergy and food intolerance

Updated: Mar 30

I hear so many people use the word food intolerance and food allergy interchangeably, without understand they are totally different things!


I want to give you the breakdown of how they differ and provide you with some things you can do to help manage and potentially overcome these issues.

What is a food allergy and food intolerance?

  • Food allergy describe an adverse immune response to food, specifically the proteins within (1).

  • Food intolerance is defined here as an adverse reaction to a food chemical for which no immune response (2).


What causes food allergies vs food intolerances?

Food allergies

Food allergy rates vary by age, local diet, and many other factors. Some of the most common food proteins that cause allergic responses include egg, milk, peanut, tree nuts, sesame, fish, crustaceans, wheat and soy.


Your gastrointestinal tract wall is the largest surface area in the human body that separates the internal sterile environment from the external world. In addition to processing food, the gut wall protects us from harmful pathogens through:

  • physiological means mucus layers to trap particles, bacteria, and viruses, special secretions, enzymes, bile salts, and extremes of pH, and

  • immunologic component consisting of innate and adaptive immune cells and factors, which also provide an active barrier to foreign antigens.

However, as infants the efficiency and function of this wall is not optimal due to of the developmental immaturity of the gut barrier and immune system. Consequently this alteration can lead to allergies through an increase IgE sensitization due to increased exposure to intact food proteins such as those mentioned above. The immune system when in contact with these proteins triggers TH2 immune cells to produce an inflammatory immune response.


There are other immune responses to food, such as IgG, IgM and IgA, which in healthy people generally have low concentrations of food-specific IgG, IgM, and IgA antibodies in their serum. IgG antibodies naturally increase in the first months after the introduction of a food and then generally decrease. However, for some people such as those with coeliac disease, inflammatory bowel disease or a IgE food allergy, they may have high levels of food-specific IgG and IgM antibodies (1).


Food intolerance

Food intolerances are not caused by one thing, rather they can have a number of origins including:

  1. Functional origin such as an enzyme deficiency e.g. lactase enzyme causing an issue with lactose.

  2. Structural origin due to anatomical and morphological changes in the gastrointestinal tract. This results secondarily in food-associated symptoms. Diverticulitis and Small Intestinal Bacterial Overgrowth (SIBO) are examples of this.

  3. Toxic reactions are due to the actions of toxins, which may be of bacterial, plant, or fungal origin, e.g. arising from food contamination.

  4. Non-toxic reactions are divided into two further principal mechanisms: immunologically (however slight difference in response and therefore not a allergy) and non-immunologically mediated reactions, e.g. salicylates, biogenic amines (such as histamine), sulfites (present in wine and medications) and sodium glutamate (flavor enhancer) (3).



What are the symptoms of a food allergy vs food intolerance?

These are both nonexhaustive lists of the variety of ways an intolerance and allergy can present. The list is potentially endless, which can make it very difficult to understand and identify. However some key symptoms have been listed:

IgE Food allergy

  • Infantile eczema (particularly facial)

  • Acute reactions: rash around mouth, urticaria, angioedema, vomiting, breathing difficulty, anaphylaxis

Food intolerance

  • Episodic/recurrent/chronic, hives/swellings, stomach/bowel irritation, headaches/migraine, fatigue/aches/pains, mouth ulcers and sinus congestion/polyps

  • In children: irritable behaviour (‘colic’, ’screaming’, disturbed sleep, leg aches and pains, ADHD), reflux (from birth), eczema/itchy rashes and nappy rash (2).



How do you test for food allergies and food intolerances?

Food allergy testing and identification can involve the following:

Allergy test results cannot be used on their own and must be considered together with your clinical history:

  • Skin prick tests (SPT), and/or allergen specific IgE (formerly known as RAST) (2).

  • Blood tests for allergen specific IgE (also IgG, IgA responses)

  • Patch testing

  • Oral allergen challenge testing which should only be done under the supervision of a clinical immunology/allergy specialist

Not recommended usually, because they are not specific to food allergies includes:

  • Total IgG testing and eosinophil counts

Alternative methods include:

  • Cytotoxic food testing, kinesiology, vega testing, electrodermal testing, pulse testing, reflexology and hair analysis (4)

Food intolerance testing a complex can involve

  • Pathology serum analysis, diagnostic imaging techniques, endoscopic examinations and histological analyses to understand the presence of causes such as chronic inflammatory bowel disease and coeliac disease etc

  • Breath testing can identify enzyme deficiencies and bacterial overgrowths

  • Other options include hair testing, however this isn't as widely accepted.


How to treat food allergies and intolerances.

The treatment for allergies and intolerances are different and are down to the individual, however there are a few things you can do whilst you are seeking professional support.

1. Allergies and intolerances

Avoid the casual food or foods.

  • Anaphylaxis to a food means long term avoidance. This is a non-negotiable requirement and primary treatment.

  • IgE, IgG, IgA and IgM allergies benefit from removal of foods as it is also their primary treatment. Some people have the potential to for the food to be reintroduced at some stage after the gut and immune system have received professional support. This is a very individual outcome and depends on the type of allergy involved.

  • Intolerances also benefit from removal of foods, but is many cases is not treatment, rather it is symptom support. Addressing the underlying cause in many people can result establishing tolerance to these foods.

When avoiding foods be mindful to:

  1. Pay careful attention to label reading

  2. Take care in when eating out

  3. Avoid cross-contact of foods with an allergen during meal preparation

  4. Be aware of language used to describe food example milk and casein (casein being the protein of milk)

2. Allergies. Natural or if needed pharmaceutical antihistamines may support. Natural options include quercetin, vitamin C and zinc* (please check with a professional before starting these)

3. Intolerances. Digestive enzymes and betaine hydrochloride* (stomach acid) support can be beneficial when it is from a functional origin. You may even from these 8 tips beneficial If it is structural origin, such as diverticulitis or SIBO, toxic or non-toxic origin, these required professional support.


* Please check with your practitioner before commencing.



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