Food intolerances are sometimes given short shrift, being dismissed as picky eating, hypochondria or faddishness – particularly as more celebrities announce that they are wheat intolerant, like Rachel Weisz, or dairy intolerant, like Victoria Beckham and Orlando Bloom.
A survey last week found that 12 million people in Britain believe they have a food intolerance, although less than a quarter of them have been formally diagnosed. Previous studies have put the real number of sufferers as low as 2 per cent of the population. But while many people wrongly believe they are sensitive to certain foods, there are also millions of us who have genuine food intolerances – but don't know it.
The charity Allergy UK claims that 45 per cent of Britons suffer from some kind of food intolerance, but experts remain sceptical. "I would be very surprised if the figure was as high as 45 per cent," says Ruth Towell, who is chair of the food allergy and intolerance group and a senior research dietician at St Thomas's Hospital. "Working out the prevalence of food intolerance is very difficult. Diagnosing an allergy is usually straightforward, but often people will prefer to blame certain health problems on a food intolerance rather than a bad diet or an unhealthy lifestyle, which can produce the same symptoms."
Patrick Holford, co-author of Hidden Food Allergies, says: "The figure for how many people have a food intolerance is not going to be very low; I would estimate that one in three people suffers from one." So how can you tell if you've got a food intolerance – and what can you do about it?
Intolerances and allergies
The first issue is distinguishing an intolerance from an allergy. An allergic reaction happens rapidly, and can be triggered by even the tiniest amount of allergen. In an allergic reaction, the immune system produces IgE antibodies, our defence against foreign substances our bodies perceive as harmful. This can result in rashes, swelling or breathing difficulties and, in extreme cases, anaphylactic shock, resulting in death.
An intolerance is defined as a temporary adverse reaction that does not involve the immune system. Reactions are likely to be less severe and can take up to three days to appear and last for weeks. In most cases, a significant amount of the trigger food must be ingested. "Someone might have four tablespoons of milk and be fine," says Towell, "but then have a fifth and feel terrible."
Whereas allergies produce IgE antibodies, some experts believe that food intolerance involve antibodies called IgGs. "The IgG antibody is the new kid on the block," says Holford. "It is often regarded as suspect; there is a lot of debate as to whether it is or isn't important." What everyone agrees on is that a food intolerance can be highly inconvenient for the sufferer. "Both people with a food intolerance and an allergy will be avoiding certain food," says Towell. "So both conditions will have an impact on their quality of life."
Food intolerances occur when people lack certain enzymes, which turn proteins into amino acids. Without them, proteins go straight into the bloodstream, leading to a range of chronic minor complaints. Traditionally, these have been considered idiopathic, meaning that there is no one specific cause. But food intolerances are now being blamed for a range of small but annoying health problems, which can be divided into five categories:
* Respiratory – rhinitis, sinusitis and asthma
* Musculoskeletal – arthritis, aching and weakness
* Gastrointestinal – vomiting, bloating, cramping, gas, nausea, diarrhoea and colic
* Central nervous system – migraine, headache, mood swings, depression and hyperactivity
* Dermatalogical – hives, eczema and other rashes
There is a strong genetic pattern to food intolerances. For example, lactose intolerance is most common in people of African, Asian, Jewish or Hispanic descent; it only affects about 15 per cent of northern Europeans. Coeliac disease is more common in Finland, where rye, barley and oats, rather than wheat, were traditionally eaten.
In many cases, intolerance to milk and eggs in early childhood can disappear by the age of five. In other cases, intolerances can develop in later life. No one is quite sure why; some believe one factor is stress, such as divorce, moving house or a bereavement or following illnesses such as septicaemia, glandular fever, a giardia infection or dysentery.
Some experts believe that food intolerance can be a result of over-exposure to foods that should form only a small part of our diets. Holford believes that "leaky gut syndrome" is often to blame. "The best way to develop a food allergy or intolerance is to drink lots of alcohol, which irritates the gut, take some paracetamol, get a gut infection, take some antibiotics and then eat cheese on toast. Do that often enough and I guarantee you'll develop a wheat or lactose intolerance."
The most effective way to cure a food intolerance is to cut that food out of your diet. This sounds simple, but identifying which food is the trigger, or even if food is the trigger, is not a simple process. In many cases a food intolerance will be obvious, in which case an exclusion diet (where you cut that food out of your diet for four to six weeks and see if the symptoms disappear) will confirm it. Problems arise when a trigger substance is so specific – a particular additive, for example, used in a range of food and drink – that to identify it on your own would be difficult.
If the trigger food isn't obvious, there are several blood-test kits on the market, most of which involve sending away a blood sample or attending a clinic. There is even a test that can be performed entirely at home: the Food Detective Food Intolerance Self-Test, which is available from larger chemists for around £50.
But the only test that has shown positive results after a clinical trial and is approved by Allergy UK is YorkTest. This works by measuring the amount of IgG antibodies in your blood, which the manufacturers say are produced when you are intolerant to a food.
Not everyone believes that this is an effective way to test for food intolerance. "The British Dietetic Association's problem with York Test Laboratories is twofold," says Towell. "The first is that we don't agree that the presence of IgG antibodies in the blood is always a sign that there is an intolerance to a food. The second is the lack of support for patients. YorkTest will send you back a list of foods that you have to avoid.
"Just giving someone a list of 20 foods to avoid is a nonsense. We believe that the best thing to do if you think you have a food intolerance is to see a dietician. They will ask you to keep a food and symptoms diary and from that, they will try to establish a pattern."
Your GP can refer you to a dietician.
"I think the BDA are possibly a bit behind on the importance of the IgG antibody," adds Holford. "I agree that it is not the only way to diagnose a food intolerance, but some people simply take the test, avoid the identified foods and move on."
Intolerance – or just a bad diet?
Adverse reactions to dairy products are caused by intolerance to lactose, the sugar in milk. This stems from a metabolic deficiency of lactase, an enzyme released from the lining of the small intestine. Lactase is required to break down lactose into glucose and galactose, so that they can be absorbed into the bloodstream. The intolerance can lead to bloating, nausea, diarrhoea and flatulence. Some sufferers do produce small amounts of lactase, so they can tolerate some milk or other dairy products. For others, however, even a small amount of milk can cause a severe reaction. Some nutritionists identify dairy products as a contributing factor in eczema and asthma. Studies have shown that it may also aggravate acne. But medical advice should always be sought before cutting major food groups out of your diet.
Sensitivity to wheat could have a variety of causes, and indeed, it is possible to be allergic to wheat. Symptoms might include sneezing, rashes, running nose, coughing, digestive problems and general aches and pains. Another common cause is coeliac disease. This is a rare sensitivity to the protein gluten, which exists in many cereals. In people with coeliac disease, gluten triggers antibodies that attack the body's own tissues. The result is gastric problems, restricted growth, headaches, fatigue and joint pains. Not all sufferers exhibit all of the above symptoms and many are unaware that they suffer from the condition until tested. The recommended treatment is a gluten-free diet.
Less is known about wheat intolerance, though many people identify wheat as a trigger for symptoms including fatigue, breathlessness, general malaise, bloating, wind, abdominal pain, diarrhoea, vomiting, weight loss and skin problems. One solution might be a wheat-free diet, though many experts say this is unnecessary and that wheat only appears to cause symptoms because it is hard to digest in the large amounts that exist in the Western diet.
According to orthodox medicine, true yeast intolerance is rare. It is only likely to affect people whose immune systems are severely compromised by another medical condition. Many alternative practitioners, however, say yeast intolerance is behind bloating, wind, diarrhoea and headaches as well as mouth ulcers, thrush, sweet cravings and mood swings. This intolerance stems from an overproduction of yeast, or candida. This can occur when a person is stressed or their immunity is low, but some nutritionists believe yeast intolerance can also be triggered by the Pill, poor diet, repeated courses of antibiotics and hormonal changes.
Common 'trigger foods'
These are the most 21 most commonly reported trigger foods, according to Cambridge Nutritional Sciences, which provides a service diagnosing intolerances:
Dairy; wheat; oats; maize; rice; white fish; shellfish; nuts; peas; kidney beans; haricot beans; eggs; chicken; pork ; beef; tomato; berries; potatoes; soya; cabbage; broccoli