As many as 20% of the population are affected by food intolerances on a daily basis. Are you or a family member one of them? Here we look at the main food intolerances, the symptoms and what you can do about them if you are affected. Knowledge is power, so read on!

Adverse food reactions are defined as any abnormal reaction following the ingestion of food. The

different adverse reactions are described as

  • food hypersensitivity, including food intolerance and food allergy, or
  • food aversion, which is a psychological avoidance of food due to conditioning to avoid adverse



Here we are discussing food intolerance, the definition of  which is a non-immunological response initiated

by a food or food component at a dose that should be normally tolerated;  food intolerances account for most adverse food responses.

Food allergy, on the other hand, is an abnormal immune response to a food protein mediated by immunoglobulin E

(IgE), non-IgE or mixed IgE/non-IgE immunological mechanisms.

The prevalence of food allergy varies affecting 1–2% of adults and less than 10% of children.

In contrast, food intolerance is estimated to affect up to 20% of the population.


Naturally occurring and present in a wide variety of foods are fermentable carbohydrates

termed ‘FODMAPs’ (denoting fermentable oligo- di- mono-saccharides and polyols). This group

of carbohydrates has been identified to trigger symptoms in patients with functional GI symptoms such as in irritable bowel syndrome (IBS).

The low FODMAP diet reduces intake of carbohydrate subgroups including

(i) excess fructose present in foods such as honey, apples and mangoes,

(ii) lactose present in milk and yoghurt (in the presence of lactase deficiency),

(iii) polyols (largely comprised of sorbitol and mannitol) present in avocado and pears,

iv) fructans present in wheat, onion and garlic, and

(v) galacto-oligosaccharides present in legumes and nuts.

Consumption of a high FODMAP diet in sensitive individuals is thought to be associated with

lower Gastrointestinal tract (GIT) symptoms of

  • abdominal pain,
  • bloating,
  • flatulence, and
  • altered bowel habits.

Randomized controlled trials using a low FODMAP diet have noted improvement in overall abdominal symptoms,

pain, bloating, and bowel habit.

Improvement in symptoms with the use of the low FODMAP diet in cohorts of IBS patients have been shown to vary

between 50–80% improvement, so well worth trying.

FODMAPs cause a problem firstly because , short-chain poorly absorbed carbohydrates present in the small intestine

have an osmotic effect, increasing water delivery to the small bowel.

Secondly, the delivery of rapidly fermentable carbohydrates to the colon leads to fermentation by colonic bacteria resulting in increased gas production.

Short-term studies have suggested a low FODMAP diet may result in reductions in overall bacterial abundance, so well worth taking probiotics if you engage with this diet.


The two parts of wheat relevant for discussion for food intolerance are the protein and carbohydrate

fractions. Gluten is the main storage protein of wheat grains and is a complex mixture of hundreds of

related but distinct proteins, mainly gliadin and glutenin. Similar storage proteins exist in rye, barley

and oats, and are collectively referred to as “gluten”. Gluten contributes to the dough quality and

is predominantly found in sources such as pasta, cake, pastries and biscuits, but can also be used as

a binding and extending agent in processed foods.

Other low molecular weight proteins found in wheat and related cereals are called amylase/trypsin inhibitors (ATIs). Although these contribute less than 4% of the total protein content, they can still cause problems.

Another part of the protein component is wheat germ lectin agglutinin known for their binding action to expressed sugars.

Gluten is associated with GIT symptoms including

  • abdominal pain,
  • bloating and
  • bowel habit abnormalities, so-called ‘non-coeliac gluten/wheat sensitivity’ (NCG/WS).

In addition to the GI tract response, there are various systemic manifestations reported to be associated

with wheat intake, including disorders of the neuropsychiatric area such as

  • “foggy brain”,
  • headache,
  • fatigue
  • dermatological and
  • musculoskeletal symptoms (i.e. leg or arm numbness).

Amylase/trypsin inhibitors (ATIs) in wheat activate innate immune cells via stimulation of toll-like receptor 4, which then induce the release of pro-inflammatory cytokines and chemokines, leading to an unbalanced inflammatory immune response.

Wheat lectin agglutinin has shown that it can increase intestinal permeability by its epithelial damaging and immune effects. This increase in gut wall hyper permeability or “leaky gut” can increase cause foggy brain and joint and muscles aches, as well as exacerbate food intolerances.

Management of wheat intolerance, particularly for GIT symptoms,

may be best tackled by implementing the low FODMAP diet, and not just a gluten free diet. This is because

of the coexistence of fructans and gluten in wheat.

Histamine intolerance

Histamine is a biogenic amine that is present in the body but also in many foods.

Foods containing histamine.

Meat – Sausages of any kind, salami, air-dried and corked meat, ham, etc.

Fish – Dried or preserved fish, such as herring, tuna, mackerel, sardines and anchovies,

seafood, fish sauces.

Cheese – All types of hard, soft and processed cheese

Vegetables – Eggplant, avocado, sauerkraut, spinach, tomatoes incl. tomato juice/ketchup

Drinks and liquids – Vinegar or alcohol of all kinds, mainly red wine, beers, champagne, whisky and cognac; alcohol in general reduces degradation of histamine and increases the permeability of the intestine and can therefore worsen the symptoms of histamine intolerance.

Histamine intolerance can have an effect on many body systems, and not just the GIT. The symptom of Histamine intolerance include:

Skin Itching – sudden reddening of the skin (flush symptoms) on the face and/or body, very rarely hives, angioedema (different to urticaria) and other exanthemas

Digestion – Nausea, vomiting, diarrhea, abdominal pain

Circulation – Tachycardia, drop in blood pressure, dizziness

Respiratory – Chronic nasal flow, sneezing attacks

Neurological – Headaches, migraines

Gynecological – Menstrual cramps

Histamine intolerance results from an imbalance of accumulated or ingested histamine and the

reduced ability to degrade histamine. In healthy individuals, amine oxidases can quickly detoxify

histamine ingested with food, while people with low amine oxidase activity run the risk of histamine toxicity. Diamine oxidase (DAO) is the main enzyme for the metabolism of ingested histamine.

Histamine produced in the body seems to have less effect on histamine intolerance, except in situations such as mastocytosis when an increased number of mast cells are activated to spontaneously release histamine  in the body.

Before diagnosing histamine intolerance, other food intolerances, GI disease, IgE-mediated food allergies and underlying mastocytosis should be excluded first. If histamine intolerance is still suspected, avoidance of histamine-rich foods for 3 to 4 weeks is recommended..

A low histamine diet is the first priority in management and as a supporting measure, the enzyme DAO can be taken orally approximately one hour before histamine-rich food is consumed.


Food Additives

Thousands of different food additives are used throughout the food industry for various functions,

especially to preserve food and improve taste or appearance. They are generally synthetic and natural

substances that cannot be consumed alone as food themselves. Food additives are classified based

on their function and property including

  • preservatives,
  • flavors,
  • emulsifiers,
  • thickeners,
  • humectants,
  • firming agents and
  • flavor enhancers.

A small number of additives have been implicated in IgE-mediated or other immunological or non-immunological adverse reactions.

Here are some examples of foods containing natural and added food chemicals thought to induce gastrointestinal and extra-intestinal symptoms in gastrointestinal conditions.


Natural food chemicals:

Amines – Cheese, chocolate, banana, ham, fish

Glutamate – Tomato

Salicylates – Apples, tomatoes


Added food chemicals:

Antioxidants – Oils, margarine

Benzoates – Soft drinks, cordials

Colours – Confectionary, jelly

Monosodium glutamate (MSG) – Chinese take-away, packaged foods

Nitrates – Deli meats

Propionates – Breads

Sorbic acid – Processed cheese slices

Sorbates –  Soft drink, cordials, dried fruit


The prevalence of self-reported symptoms to food additives has been found to be 0.01–0.23% in

adults, and  as high as 2–7% prevalence in children with atopic dermatitis.

Food additives and chemicals are thought to contribute to both GIT symptoms similar to IBS, as well as extra-intestinal symptoms including

  • urticaria,
  • headache,
  • eczema,
  • rhinitis,
  • nasal congestion, or post nasal drip.

We know that these chemicals cause real world problems.

  • One study of patients with a dual diagnosis of fibromyalgia and IBS, showed that a 4-week dietary exclusion of glutamate reduced more than 30% of symptoms in the vast majority of the patients.
  • The prevalence of GI symptoms following consumption of higher doses of salicylates from aspirin and other non-steroidal anti-inflammatorydrugs has been suggested to be between 10-20% in those with asthma,
  • Specific mechanisms have been proposed to link asthmatic reactions to sulphites. with mode of exposure likely to be an important factor with inhalation of sulphur dioxide and the warm acidic environment of the mouth possibly triggering respiratory symptoms.
  • Additionally, it has been proposed that the parasympathetic system may be involved whereby inadequate sulphite oxidase results in accumulation of sulphite, causing  bronchoconstriction.
  • More recently, evidence has shown two commonly used emulsifiers, carboxymethylcellulose and polysorbate-80, can induce low grade inflammation and obesity/metabolic syndrome, and may impair the epithelial barrier.
  • Similarly, nanoparticles such as titanium dioxide,a substance added to foods as a whitening agent, has been shown to alter nutrient absorption and disrupt the epithelial barrier impairing gut homeostasis.
  • It has been proposed that food chemicals may induce a non-specific antigen-induced pseudo-allergic hypersensitivity.

Sucrose and Starch

When there is an absence or reduction in sucrase and isomaltase enzymes, dietary carbohydrates such as sucrose and starches may result in symptoms due to the inability or reduced ability for absorption.

In such a sucrase-isomaltase deficiency, sucrose and starches in the lumen act as FODMAPs resulting in symptoms of diarrhoea, bloating and abdominal pain, with symptom severity dependent on residual sucrase and isomaltase activity.

Such a Sucrase-isomaltase deficiency may occur either due to genetic variants, or as a secondary or acquired event.

Dietary treatment may include restriction of sugars and starch. An alternative or adjunct therapy would be the use of enzyme replacement therapy with sacrosidase, such as Sucraid, which has shown good effect in small studies.