While food allergy is fairly uncommon, less than one per cent of the population suffer from them, food intolerances are more common. Dr Sarah Brewer clarifies the difference between food allergies and intolerances and, outlines the two most common causes - gluten and lactose
- Lactose intolerance
- Gluten intolerance
- A gluten-free diet
- Irritable Bowel Syndrome
- IBS and food intolerance
Food allergies explained
A food allergy is very different to a food intolerance. A food allergy is when an abnormal immune response triggers a potentially serious chain of immune reactions. Food allergies involve the production of histamine and a form of antibody called IgE, and can cause sudden, severe reactions such as the development of a red, itchy rash, swelling (commonly of the tongue) and constriction of the airways, which can be life-threatening.
Lactose intolerance
Lactose intolerance is relatively common and is due to a metabolic deficiency of an enzyme, lactase, that is needed to digest lactose before it can be absorbed. Lactase is released from the lining of the small intestine and breaks lactose down into two sugars, glucose and galactose, which are immediately absorbed into the blood stream. Lactase deficiency leads to symptoms that can include:
- bloating and wind
- audible bowel sounds (borborygmi)
- abdominal pain
- diarrhoea
Lactase deficiency can be present from birth (primary lactase deficiency) or can result temporarily after a bout of gastro-enteritis (secondary lactase deficiency).
Lactose deficiency is sometimes diagnosed by taking a lactose tolerance test. A solution containing 50 grams of lactose sugar is drunk and blood samples taken at intervals over the next two hours. A more reliable test is to measure breath hydrogen levels after a known amount of lactose is consumed. In normal conditions, the hydrogen content of the breath does not increase as all lactose is absorbed. If there is a deficiency of lactase however, the sugar reaches the colon where it is fermented by bowel bacteria to produce an increase in breath hydrogen content after 90 minutes. Alternatively, a small bowel sample (jejunal biopsy) can be taken which will confirm the lack of lactase enzyme.
Treatment involves following a lactose elimination diet in which soya or low lactose milk products used in place of cows' milk products.
Lactose content of different milks
Lactose (g) per glass
Yoghurt made from cows' milk has a low lactose content as bacterial fermentation breaks the lactose down.
Gluten intolerance
Gluten is a protein found in several cereals including wheat, rye and barley. Gluten sensitivity causes coeliac condition (gluten sensitive enteropathy), which can develop at any age. It is relatively common, affecting around one person in 2,000 - in Ireland, the incidence is one person in 300. The condition is commonly diagnosed in the third to fourth decade and affects more females than males.
Symptoms of coeliac disease vary. Some sufferers develop few problems and are unaware of their condition. Other sufferers develop a variety of symptoms that can creep up over months or years, and can include:
- tiredness
- generalised feelings of being unwell
- breathlessness
- abdominal pain
- bloating and wind
- diarrhoea
- vomiting
- passing pale, bulky, offensive, fatty stools that float (steatorrhoea)
- weight loss
- some sufferers are prone to mouth ulcers and sores at the corner of their mouth
- there may be skin changes including pigmentation, scaliness, easy bruising and a rash known as dermatitis herpetiformis
The symptoms of coeliac disease are due to abnormal changes in the lower part of the small intestine, the jejunum. These are brought on by exposure to dietary gluten and resolve when following a gluten-free diet. The condition seems to be a hypersensitivity to gliadin, a small protein (polypeptide) in gluten. This may be a direct toxic effect or be triggered by an over-zealous immune system - possibly brought on in susceptible people by exposure to a particular virus (Adenovirus 12).
The diagnosis is made most accurately by taking a biopsy of the small intestine (patients swallow a special capsule containing a small cutting device activated by remote control under X-ray vision). In coeliac condition, this will show abnormal smoothness of the jejeunal lining, in place of the normal tiny finger-like projections (villi). Signs of inflammation are also present. The biopsy is usually repeated up to three times - once when eating gluten, when following a gluten-free diet and when a gluten challenge is given to confirm the diagnosis. More recently, antibody testing is used to detect IgA antibodies associated with the condition, such as antigliadin antibody (AGA) and endomysial antibody (EMA).
Treating gluten intolerance
Treatment is with a gluten-free diet, which produces a rapid improvement within a few weeks. This diet must be followed for life - which may prove difficult in the long-term. Sufferers can obtain gluten-free products on prescription from the doctor and have to replace cereal-containing foods such as bread and cakes with gluten free versions. They must also check food labels carefully to look for hidden gluten in products such as soups, stock cubes and dessert mixes etc. Vitamin and mineral supplements are important to guard against nutrient deficiency.
A gluten-free diet allows you to eat
- Special gluten-free bread, crispbread and pasta
- Gluten-free flour, soya flour, potato flour, pea flour, rice flour
- Soya bran, rice bran
- Gluten-free biscuits, cakes
- Gluten-free breakfast cereals
- Rice, tapioca, sago, arrowroot, buckwheat, millet, maize, corn
- Fresh or frozen meat, poultry, offal
- Plain fish (fresh or frozen)
- Eggs, plain cheese
- Milk, cream, butter, margarine and oils
- Vegetables and potatoes
- Fruit and nuts
- Tea, coffee, fruit juice
- Sugar, jam, marmalade, honey, jelly
- Herbs, spices, mustard, vinegar, salt, pepper
- Wine, beer, spirits etc
Forbidden foods include
Irritable Bowel Syndrome
IgE antibodies are linked with severe food allergies and IgA antibodies are linked with coeliac condition. Researchers now increasingly feel that another type of antibody, IgG, causes food intolerances that might lead to long-term health problems such as irritable bowel syndrome.
Irritable bowel syndrome (IBS) is the most common problem to affect the gut. At least one-third of the population are affected at some time during their life, even if only mildly. It usually develops between the ages of 15 and 40 but can come on at any age. As many bowel problems cause similar symptoms initially, IBS is not a diagnosis you should make yourself - always seek medical advice.
IBS is a problem of bowel function and the diagnosis is made on the basis of symptoms alone. For your doctor to diagnose irritable bowel syndrome, you must have had at least 12 weeks, (which need not be consecutive) in the preceding 12 months of abdominal discomfort or pain that has two of the following three features:
- Pain is relieved by opening your bowels; and/or
- Its onset is associated with a change in frequency of stools; and/or
- There is a change in form (appearance) of the stools.
The following symptoms also support the diagnosis of IBS:
- Fewer than three bowel movements a week
- More than three bowel movements a day
- Hard or lumpy stools
- Loose (mushy) or watery stools
- Straining during a bowel movement
- Urgency (having to rush to have a bowel movement)
- Feeling of incomplete bowel movement
- Passing mucus (white material) during a bowel movement
- Abdominal fullness, bloating or swelling.
Typically, motions are small, frequent, pencil-like, or resemble rabbit droppings, but some people experience mainly diarrhoea (symptoms 2, 4 or 6 above) while others experience mainly constipation (symptoms 1, 3 or 5). Some people experience both types of symptom at different times.
If your doctor diagnoses IBS, he or she is likely to recommend painkillers (eg paracetamol, ibuprofen, codeine phosphate) or medication that reduces intestinal spasm (eg peppermint oil, alverine citrate, mebeverine). Laxatives and anti-diarrhoeal medication is also used where necessary.
IBS and Food Intolerance
People with IBS often notice that certain foods tend to bring on their symptoms.
Anti-food IgG antibodies can be detected in a pin-prick sample of blood using an immune ELISA test. The test exposes blood to up to 113 different food antigens and the strength of any antigen-IgG reactions is measured using fluorescence. This shows how much antibody has reacted with each food, which in turn gives an indication of the severity of the food intolerance. Once the results are known, you are advised to avoid eating the foods to which you are intolerant and, in most cases, symptoms will improve significantly. Interestingly, once you have avoided foods to which you are intolerant, the immune system seems to reset itself, the specific IgG levels come down and may stay down. Many people have managed to re-introduce problem foods a year or two after their symptoms have gone without further ill effects.
An independent, blinded audit on behalf of Allergy UK showed that around 52 per cent who rigorously altered their diet experienced quite significant reduction in long-term symptoms following the test. Over 70 per cent of people who benefited from the test, reported continued health improvements one year later. A copy of the report is available here.
A clinical study carried out by the University of York investigated the effectiveness of a three-month exclusion diet, based on the YorkTest FoodScan test, in 150 people with irritable bowel syndrome. The study was a double-blind, randomised controlled trial which is one of the most rigorous forms of research. Volunteers were randomised to receive either a diet excluding all foods to which they had IgG antibodies, or a sham diet excluding the same number of foods but not those to which they were sensitive. Symptom severity and quality of life were recorded at the beginning and at the end of the three month trial. The results showed that the true diet was significantly better than the sham diet in reducing symptom severity scores. Response to the diet was significantly affected by how well people stuck to the diet, and the number of foods to which they were sensitive. When these factors were accounted for effectiveness of the diet was even greater. Reintroduction of the offending foods also led to a greater return of symptoms in the true diet group. The researchers concluded that a clinically significant improvement can be achieved in some patients with IBS using a food elimination diet based on IgG food antibodies.
Food intolerance testing is now available from a number of pharmacies and health food shops. You can order a test kit through Lloyds pharmacies, for example, and will receive a kit through the post to obtain a pin-prick sample of blood which is then sent back to York Nutritional Laboratory.
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