Food allergy and intolerance

Food allergies

Recent research shows 39% of children and 30% of the adult population experience at least one atopic (classic allergic) symptom, with allergy accounting for 6% of visits to GP surgeries, this appears an increasing problem.

Of these allergic events, it is estimated around half are due to food allergies. In addition to this 45% of the UK population have at least one significant masked food allergy and 70% of the world’s population are lactose intolerant, including virtually all Asians and around 12% of the UK’s population. 1% of the UK population also suffer celiac disease which is the most sinister form of gluten intolerance.

Despite a clear and seemingly increasing incidence of food allergy and intolerance it remains relatively under-diagnosed and massively under treated. In part this would appear to be due to the complex nature of food allergy and intolerance and limited medical recognition of and treatment for these conditions.

Adverse food reactions

These include classic or atopic allergies, which are the ones typically recognised by GPs, and tested using skin-prick testing where a sample of the suspected allergen is inserted under the skin and the reaction measured by the extent of the ‘nettle rash’ which forms. This reaction is mediated by immune cells called type E immunoglobulins (IgE).

In addition to this, many people suffer immunoglobulin G type reactions (IgG) which, although it is a different form of food allergy is described by the medical professions as food intolerance, to distinguish it from the classic allergic reaction. The reason for this is that classic (IgE) reaction is considered sinister and potentially life threatening and masked (IgG) reactions are not as serious and are never life threatening.

In addition to allergies many people experience other intolerances to food, including lactose (milk sugar) and gluten intolerance (including celiac disease) which are due to the deficiency of an enzyme, lactase in the case of lactose and glutease in the case of gluten.

Lactose is found in milk and other dairy foods and a deficiency of lactase manifests as a failure to digest milk sugar and produces digestive and gut symptoms, such as bloating, gas, constipation, diarrhoea and abdominal pain with the consumption of dairy produce.

Gluten is a spongy protein found in wheat, barley, rye and oats. Gluten intolerance typically causes failure to digest these foods and can lead to similar symptoms as lactose intolerance. In severe forms of gluten intolerance the gluten damages the absorptive part of the gut and leads to multiple nutrition deficiency with associated fatigue and malaise. In severe cases this can be fatal and Gluten intolerance has been shown to increase the risk of developing bowel cancer.

Food allergy and intolerance testing

All of the above forms of food allergy and intolerance can be tested for, with varying degrees of success. Many people, however, have adverse reactions to foods for which there are no medically recognised tests. These include reactions to chemicals produced in foods by bacterial action called vasoactive amines, such as tyramine.

In some people a sudden increase in these vasoactive amines can lead to diarrhoea, abdominal pain, migraines and skin flushing. The balance of organisms residing in the gut impact enormously our ability to digest and utilise nutrients and either a lack or excess of some organisms can lead to specific patterns of food intolerance.

For example excess gas and bloating, often with indigestion, constipation and/or diarrhoea, and in some people fatigue, autointoxication and brain fog with the consumption of carbohydrates suggests an excess of yeasts, a poor ability to digest tough celluloses such as inulin, found in onions, cabbage, celeriac, leeks and pulses, causing gas and bloating suggests a lack of fermentative bacteria.

Poor digestion of protein rich foods such as meat and fish could be a sign of hypochlorhydria (lack of hydrochloric acid) or, more unusually, a lack of putrefactive bacteria.

Food sensitive or intolerant

Many people are simply sensitive to foods or do not tolerate certain foods well. This appears to be due to a lack of enzymes required to either digest or metabolise the food. An example of this is the variance in people’s tolerance of alcohol. This is dependant on levels of key enzymes such as, alcohol dehydrogenase in the liver which determines the speed which alcohol is broken down.

There are a host of enzymes in our liver which largely determine the rate at which we detoxify chemicals in our food and indeed, other substances such as drugs. For example, some people handle caffeine better than others, some need more of drugs such as paracetamol to have a pain killing effect and some people are more at risk from the toxic effects of substances such as, benzopyrenes in red meat and oestrogens, an excess of which can increase the risk of bowel and breast cancers respectively. Some people are simply sensitive to chemicals in foods such as salicylates, solanins, azo dyes, sulphites and benzoates.

All of these adverse food reactions can now be measured empirically to a lesser or greater extent. An increasing array of functional tests enable assessment of these reactions, although the ‘gold standard’ remains a clinical process known as an ‘elimination and challenge’ test.

This describes the process whereby a suspected offending food(s) is eliminated from the diet, usually for a minimum of 3 weeks, and then reintroduced in a controlled challenge tests. A positive test would involve the marked reduction in key symptoms during the elimination phase and then a return of these symptoms (usually with a vengeance) on reintroduction. This is a low cost but comparatively ‘long winded’ alternative to empirical testing and whilst it does not determine the nature of an adverse food reaction, is effective at establishing the offending food(s).

Types of food intolerance

  • Classic Allergy – Typically manifests as itching, swelling and soreness and often of the lips, mouth or throat and can be extremely dangerous. It can also cause other histamine reactions including indigestion, diarrhoea, asthma, eczema, joint pain and urticaria (nettle rash). Symptoms develop within 20 minutes of exposure and can be cumulative. Testing includes skin prick testing and blood testing, neither of which is essentially conclusive if the reaction is localised.
  • Masked Allergy – Can manifest as a wide variety of symptoms which include gas, bloating, constipation and/or diarrhoea, abdominal pain, migraine, sinusitis, sore throat, excess mucous, acne, eczema, headache, low mood, low energy, cravings, low immunity, muscle pain and joint pain among others. Symptoms can take up to 72 hours after exposure to manifest, hence the cause is often masked. The effects are often cumulative and compound as many people react to several foods. Testing includes a blood test which has 85% accuracy.
  • Lactose Intolerance – Manifests as gas, bloating, abdominal pain, constipation and diarrhoea with the consumption of dairy produce. Symptoms are often dose dependant with greater reactions taking place to the greater sources of lactose, therefore the reaction to milk and cream is usually greater than to cheese, yoghurt, butter and ghee. Lactose intolerance can be tested using a breath hydrogen test and more effectively using the elimination and challenge process.
  • Gluten Intolerance –  The symptoms are similar to those associated with lactose intolerance. In coelic disease the condition is also associated with lassitude, weight loss and general malaise. The symptoms can also be dose dependant with typically greater reactions to wheat than to barley, rye and oats. Coeliac disease along with gluten intolerance can be tested for in the blood and again are identifiable with the elimination and challenge process.
  • Intolerance of vasoactive amines – This typically manifests as diarrhoea, migraine, abdominal pain and skin flushing with specific fermented foods, including coffee, vinegar, some alcoholic beverages, some forms of fish and some beans. This might seem an inconsistent reaction as the levels of vasoactive amines vary in foods. A new test has recently been developed to test this reaction but is not yet widely available.
  • Yeast overgrowth – This typically manifests as bloating and gas and might include constipation, diarrhoea, indigestion, abdominal pain and in some fatigue, autointoxication, lapses in memory and concentration, all with the consumption of sugar, carbohydrate and yeasty foods. This can be identified using a stool test.
  • Dysbiosis (bacterial imbalance) – This typically manifests as indigestion, gas and bloating with fibre rich vegetables, although unusually it can cause difficulty digesting other foods. This can again be identified with use of a stool test.
  • Food sensitivities – These can manifest as digestive dysfunction, including gas, bloating, indigestion and diarrhoea but can also cause a raft of additional symptoms, including soreness, joint pain and rashes. In mild forms, these might simply cause a prolonged ‘toxic’ reaction to caffeine and alcohol. A new range of functional tests is enabling better detection of these conditions, although elimination and challenge testing remains the most effective way of detecting these sensitivities.

Please note the above is not designed to replace thorough assessment of your symptoms by a health practitioner and it is strongly recommended you seek medical advice if you have a severe or disturbing reaction to food. It is also important you continue to avoid those foods to which you have a known adverse reaction.

About The Author

Peter Cox is a Clinical Nutritionist located in Westminster, London. He typically sees clients from the surrounding areas of Kensington, Camden Town and Paddington.

For more advice about Food allergy and intolerance please contact Peter at or on 07788 447843.

Find out more about Peter’s work by visiting his GoToSee profile page here


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