Food allergy and food intolerance

Food intolerances are different to food allergies. An allergy elicits an acute, almost immediate reaction; the worst of which is anaphylaxis. Food intolerance is less severe and notoriously difficult to test. Intolerance is usually because the body is lacking an enzyme that is needed to properly digest and eliminate a food or substance. Symptoms may be delayed and might include bloating, headaches or skin rashes. Skin prick testing and laboratory blood tests are available but the most effective, accepted and accurate way of identifying problem foods is via an elimination diet.


Elimination diet

Vegetables in box

An elimination diet is a free, non-invasive way of working out if you have a food sensitivity. You don’t need any pills or potions, just a fair amount of will power. Compliance and commitment are key to getting results. However, an elimination diet should be followed for the shortest time possible to bring about symptom improvements.Before you embark on an elimination diet, arm yourself with all the information you might need. Consult a qualified health professional to ensure your nutritional requirements are met and to address any other considerations. For example, where testing for coeliac disease is recommended, do not eliminate any foods from your diet until the tests have been completed.

Start by removing suspected foods and food groups – dairy, eggs, caffeine and alcohol (to name a few) for 6-8 weeks. A useful practical tool is to create a comprehensive list of ‘foods to exclude’ and ‘foods to include’ and to keep a food diary of how you feel, your symptoms and their severity etc.

After the period of elimination, reintroduce one food at a time from the exclusion list in normal amounts. Test the food on its own on an empty stomach. If symptoms return within 48 hours, then you probably have your answer. Leave at least two days between testing different foods. If there is no reaction after four days, bring the food carefully back into your diet. If you do experience a reaction, wait until you feel well again before continuing the reintroduction and avoid the culprit food for three months before re testing.

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If you suspect you have an allergy or intolerance or if you are breastfeeding, pregnant or taking any medication, you should consult with your doctor before making any dietary adjustments.

Common intolerances



Fructose is a natural sugar found in fruits, honey and some syrups. If you suspect you have a sensitivity to fructose, you should also try to avoid sucrose (table sugar), high fructose corn syrup, fruit and fruit juices, sorbitol and sweetened juices. Common signs of fructose intolerance include abdominal pain, gas and bloating and diarrhoea. The FODMAP diet is a new approach to managing IBS which may be effective in this circumstance.



Wheat is one of the most commonly cited foods for causing digestive upsets including abdominal bloating. When trying to decipher wheat intolerance, it is important to eliminate flour and flour based products entirely as well as other foods which may contain wheat or wheat-derived ingredients. Wheat intolerance varies between individuals with some people able to tolerate alternative grains. If you suspect you have wheat intolerance, try eliminating wheat entirely. You may find that you can tolerate small amounts of older varieties of grains such as spelt or kamut which are higher in fibre, lower in gluten and more nutritious.


Gluten is the glue-like protein found in many grains but especially in wheat, rye and barley. Its elasticity makes it a key part of many bakes. Some people are intolerant to the gluten in all of these grains, others just find wheat the trigger. A diet high in refined carbohydrates can contain significant quantities of gluten, which can effectively ‘glue up’ the digestive system. If you have discovered you cannot tolerate any gluten containing grains, try rice, corn and potato flours. However, before you embark on any elimination diet, be sure to consult your GP. It is essential that if you suspect gluten to be a problem that you make no changes to your diet until you have completed all of the appropriate medical tests to determine what the problem may be. This is because if you eliminate gluten before tests are completed for coeliac disease then you risk a false negative result.

Sugar in hands

Glucose intolerance is the umbrella term given to metabolic conditions which cause elevated blood glucose levels. If you have impaired glucose tolerance (IGT) or impaired fasting glucose (IFG), your body is not using glucose (sugar) properly. This may result in higher than normal blood sugar levels – a condition known as hyperglycemia. Diagnosis of either IGT or IFG requires medical guidance and is through blood test. Symptoms include excessive thirst, dry mouth, fatigue, blurred vision and frequent urination. It is important to seek medical advice if you suspect you have an intolerance to glucose.

Pouring milk into glass

All animal milks contain a sugar called lactose. We make an enzyme in our gut called lactase to digest the lactose in milk. Without lactase, the sugar is left to ferment in the gut and causes symptoms such as bloating, wind and diarrhoea. Many adults do not produce enough lactase, so suffer from what is known as lactose intolerance (essentially a lactase deficiency). Those who are intolerant to lactose you may be able to tolerate a little butter, cheese or yogurt before symptoms arise. Others choose to avoid dairy products completely.

Glass of wine

Alcohol intolerance may be caused by alcohol or the food the alcohol is made from (e.g. grapes from wine, grains from whisky). Alcohol can affect the integrity of the gut which may explain why some people experience digestive discomfort to food when it is coupled with drinking alcohol. Red wine is a common trigger, followed by whisky and beer. Alcohol intolerance can cause unpleasant symptoms such as nasal congestion and skin flushing. Once again, intolerance is linked to an enzyme deficiency making it hard for the body to break down alcohol. Intolerance may also be due to other ingredients commonly found in alcoholic beverages (especially beer and wine) including sulphites, preservatives or chemicals.

Glass of beer

Histamine occurs naturally in certain foods. We produce an enzyme called diamine oxidase to help break down the histamine in certain foods. Like with many intolerances, some people do not produce enough of this enzyme and consequently when they eat histamine containing foods they suffer symptoms such as headaches, skin rashes, itching, diarrhoea and abdominal pain. Foods that are particularly high in histamine include: wine, beer, cider, pickled foods, cheese, tofu, soya sauce, processed meats, smoked fish and chocolate. More information on histamine intolerance can be found at

Loaf of bread

Yeast is present in a variety of foods, commonly bread, baked products and alcoholic beverages. Yeast intolerance has a wide range of symptoms including flatulence, bad breath, fatigue, irritability, cravings for sugary foods, stomach cramps, bad skin and indigestion. If you suspect you are intolerant to yeast try following a yeast free diet (through elimination) for a few weeks. If there is a significant improvement then you have found your culprit!

For more information on food intolerances visit

This article was last reviewed on 24 January 2019.

Kerry Torrens is a qualified Nutritionist (MBANT) with a post graduate diploma in Personalised Nutrition & Nutritional Therapy. She is a member of the British Association for Nutrition and Lifestyle Medicine (BANT) and a member of the Guild of Food Writers. Over the last 15 years she has been a contributing author to a number of nutritional and cookery publications including BBC Good Food.

Jo Lewin is a registered nutritionist (RNutr) with the Association for Nutrition with a specialism in public health. Follow her on Twitter @nutri_jo.


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