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Is it something you ate? Food intolerance: causes and diagnosis

Food intolerance is an increasingly common self-diagnosis, but the symptoms often have other causes.

Egg with a sad face drawn on it to symbolise food intolerance
Keep a food diary to eliminate foods which can cause upset

The number of people who believe they are suffering from food intolerance is growing, yet the condition is notoriously hard to diagnose accurately. It is not the same thing as an allergy and the symptoms are vague and easily put down to other causes such as irritable bowel syndrome. They can be many and varied, ranging from migraine, bloating, diarrhoea, and lethargy to just feeling generally unwell.

According to one survey, conducted for a company that sells food intolerance tests, it is possible that around 45 per cent of people over the age of 50 have the condition, but the problem for GPs is that food intolerance is harder to pin down than a food allergy. Eat a food you are allergic to and the chances are you will see the tell-tale rash, swelling or running nose of an allergic response within a few minutes. When you’ve eaten something to which you’re intolerant, you may not see any reaction for hours, even days, by which time you will have eaten other foods and the link to the culprit food will be harder to establish. It’s also possible you may be intolerant to more than one food.

Because food intolerance is so hard to pin down accurately, it often misdiagnosed and mistreated. As Professor Nick Read, a consultant gastroenterologist, explains: “Modern medicine is not good at treating unexplained illness. Doctors often struggle to know what to recommend, when they can’t make a definitive diagnosis.” For this reason, the true number of food intolerance sufferers is hard to establish, although Allergy UK, which now runs a food intolerance awareness service (FIA), estimates that it probably runs to several millions.

Causes of food intolerance

Eating too much of the same type of food, eating in a hurry, or living a stressful lifestyle are all thought to be contributory factors. Sometimes there is an identifiable physical cause; lactose intolerant people, for example, lack the enzymes needed to absorb a protein found in dairy food, and suffer digestive problems as a result. According to Allergy UK, symptoms may also be a reaction to natural food chemicals such as caffeine, or to additives, such as monosodium glutamate (MSG). As dietician Jacqui Lowdon says: “There are a wide variety of possible offending foods. Pinpointing the exact cause can be difficult.”

Getting treated for food intolerance

A few GPs do have a special interest in food intolerance, or may be able to refer you to a dietician, who is the person best qualified to advise on special diets for medical conditions. Keeping a food diary of everything that you eat or drink over two to three weeks will help your GP to decide whether you do have a food intolerance.

The current gold standard treatment is the elimination and challenge diet, which involves avoiding foods for between five to 10 days and then re-introducing the foods one at a time to identify the culprit ingredient. However, the results are difficult to analyse and, as Professor Nick Read points out, it’s very easy to omit too many foods from your diet and risk becoming malnourished. The more foods you cut out, the more likely you also are to become intolerant to those that are left in your diet, so you should never try an exclusion diet without expert advice.

Self help for food intolerance

If you don't feel you have received adequate treatment on the NHS, private help for diet and nutritional problems is available but is complicated by the variety of professional titles. It is worth remembering that dieticians are the only professionals qualified to advise on special diets for medical conditions, and they are the only specialists in this field to be regulated by Government. Their qualifications can be checked at the Health Professions Council website. Expect to pay between £65 - £105 for a first consultation with a private practitioner.

A nutritionist is only qualified to advise generally on food and healthy eating. They also do not have to be registered to practise, although they may be, with bodies such as the Nutritional Therapy Council, or the Nutrition Society

Be very cautious about spending money on any tests you see advertised. The official Government advice is that there is no one reliable test for all intolerances. Allergy UK, which evaluates products designed for allergy and intolerance sufferers, goes further, saying that some blood tests, vega electro acupuncture tests (which involve electrodes placed over an acupuncture point in the toe), applied kinesiology (which examines muscle response to a suspected intolerance) and hair sample testing are unproven. If you do decide to buy a test, look out for a CE mark on the pack, as this means the test has been passed by UK medicine and healthcare product regulators as safe and fit for purpose


The opinions expressed are those of the author and are not held by Saga unless specifically stated. The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.