Condition - So what are food allergies and intolerances?
Food Allergy and Intolerance Week starts on 23rd January this year. According to the NHS, between one and two in every 100 people in the UK have a genuine food allergy, but many more people have a food intolerance. But what’s the difference?
A food allergy is when the immune system generates an adverse reaction to specific proteins found in food. The symptoms of a food allergy typically develop within a few minutes to an hour after you have eaten the food. Specialised cells called antibodies are produced by our immune systems, which help to identify potential threats to your body, such as bacteria and viruses, and signal your immune system to release chemicals to kill the threat and prevent the spread of infection. In food allergies, a type of antibody known as immunoglobulin E (IgE) falsely targets a certain protein found in food as a hazard to your body. The next time you eat that food, the IgE antibodies trigger the release of a number of chemicals, of which the most important is histamine.
The most common signs of an allergic reaction, such as localised itching, burning and swelling, are caused by histamine. Other typical symptoms of a food allergy include nausea, vomiting, cramping and diarrhoea. Anaphylaxis, a life-threatening allergic reaction that can cause breathing trouble and dangerously low blood pressure, is caused when the immune system goes into ‘overdrive’ and releases massive amounts of histamine into your blood. Anaphylaxis is a medical emergency and, without prompt treatment, it can lead to coma and possibly death.
In children, the foods that most commonly cause an allergic reaction are milk, soya, peanuts, eggs and wheat. The majority of children will grow out of their food allergies by the time they start school. Peanut allergies, however, are usually more persistent. An estimated 80% of children with peanut allergies remain allergic to peanuts for the rest of their life.
In adults, the foods that most commonly cause an allergic reaction are fish, shellfish, nuts and peanuts. Food allergies that develop during, or persist into, adulthood are likely to be lifelong allergies and the offending food has to be avoided entirely.
Food allergy can be diagnosed by means of skin-prick tests to various foods or by a RAST (radioallergosorbent test) on a blood sample.
Food intolerance reactions are of slower onset than allergic reactions, don't involve the immune system and aren't usually life-threatening. Food intolerances, however, may cause unpleasant symptoms, including nausea, bloating, abdominal pain and diarrhoea.
Almost any food can cause a reaction, but foods eaten most regularly are often the main suspects; these may include wheat and dairy products, closely followed by other gluten grains, eggs and yeast. Symptoms may be delayed for hours or even days after eating the food, making it very difficult to pinpoint the offending food.
Food intolerances can occur due to lack of specific chemicals or enzymes needed to digest food, e.g. lactose intolerance is a common food intolerance that affects at least one out of ten people. Lactase is an enzyme that is in the lining of the gut. Lactase breaks down lactose, a sugar found in milk and most milk products. If there is not enough lactase in the gut to digest lactose, it is used by bacteria to form gas, which causes bloating, abdominal pain and sometimes diarrhoea. Another common example is a deficiency of an enzyme called alcohol dehydrogenase. Drinking even small amounts of alcohol can make affected people feel unwell.
Some people have adverse reactions to chemical preservatives and additives in food and drinks, such as sulphites, benzoates, salicylates, monosodium glutamate, caffeine, aspartame and tartrazine. Benzoates and salicylates occur naturally in many different foods, including fruits, juices, vegetables, spices, herbs, nuts, tea, wines and coffee. Sulphites are used to preserve dried fruit, canned goods and wine and can trigger asthma attacks in sensitive people.
The easiest test for food intolerance is to remove the food from your diet, see if symptoms improve and then try reintroducing the food. If symptoms return, an intolerance is likely. Alternatively, a blood test can be done. If a food intolerance is confirmed, the food should be avoided for at least three months and then gradually reintroduced. The good news is that there are many tasty substitutes to the common food intolerance culprits. For example, coconut butter can be used as a dairy-free spread and supermarkets now are very good at providing ‘free from’ ranges. Lactose intolerance can be tested for more thoroughly using a lactose tolerance test; a digestive enzyme that includes lactase may be helpful to take.
Often, what people think may be food intolerance can be linked to a poor digestive system. Low digestive enzymes and beneficial bacteria can cause symptoms similar to food intolerance such as wind, bloating and diarrhoea, so nutritionists often recommend that people with these symptoms try taking one or both of these to support healthy digestion. A multivitamin and mineral supplement can also help to ensure that you are not lacking vital nutrients, and aid optimal gut health.