Does your skin balloon if you eat shellfish? Or perhaps you feel bloated and uncomfortable after eating too much bread.

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Many people are sensitive to foods like nuts, shellfish and cereals containing gluten. Symptoms of food reactions can include stomach upsets, skin rashes and breathing problems. Some severe reactions can even be life threatening.
Food reactions are generally classified as either allergies or intolerances. While there is evidence that both are on the increase, it’s important to understand the difference between the various types of food reactions and to avoid self-diagnosing.
Symptoms of food reactions can also be caused by other conditions, so medical diagnosis is a must. This may involve being referred to an allergy specialist or gastroenterologist for appropriate testing, depending on the symptoms.
Understanding the difference between food intolerance and food allergy is a very important step in diagnosis as it will determine the best approach for dealing with the problem. Essentially, food allergy is defined as an immune response while food intolerance is a chemical reaction.


Food allergy
Allergies are the body’s immune overreaction to a specific component of a food – usually protein. In other words, your immune system mistakenly identifies a certain food or substance as harmful.
When the immune system overreacts, immunoglobulin E (IgE) antibodies are produced against substances or allergens in the environment that are otherwise harmless – pollens, house dust, animal hair and specific food proteins. IgE antibodies to specific allergens can be detected by skin prick tests or radioallergosorbent tests (RAST).
According to the Allergy Unit at Sydney’s Royal Prince Alfred Hospital, the prevalence of food allergies varies with age but is most common in infants and children, usually beginning in the first 12 months.
The most common symptom is atopic eczema, which is an intensely itchy chronic skin rash. Other reactions include hives, stomach cramps and nausea. Some reactions may progress to life-threatening anaphylaxis, tissue swelling, breathing difficulty or collapse, which require emergency treatment.
The most common food allergies are to eggs, milk, peanuts, tree nuts and seafood. Wheat and soy can also cause allergies but they are less severe and don’t last as long. Most children tend to grow out of egg and milk allergies, but allergies to nuts and seafood often continue into adulthood. According to The Australian Society of Clinical Immunology and Allergy (ASCIA), food allergy occurs in one in 20 children and about one in 100 adults.

Food intolerance
Food intolerances don’t involve the immune system at all. They are triggered by various natural food chemicals or additives that irritate the nervous system of sensitive people. Symptoms vary from person to person; however, the most common include recurrent hives, swelling, stomach and bowel irritation, and headaches. Some people feel moody or experience flu-like symptoms.
Food intolerance reactions are usually related to the amount of food consumed. They may not occur until a certain amount of food is eaten, which is usually referred to as the ‘chemical threshold’.
Different foods can contain the same chemical or substance that causes the intolerance, but in small amounts. This chemical can accumulate in the body over time and when the threshold is finally exceeded, cause a reaction. Usually the last food eaten is blamed for the reaction but it’s usually the combination of a number of foods that causes the reaction.

Natural versus chemical

Contrary to the belief that only added or ‘artificial’ food chemicals cause reactions or intolerances, there are many natural food components or chemicals that cause food intolerances. The natural chemicals most likely to cause reactions in sensitive individuals are salicylates, amines and glutamate – for example, monosodium glutamate (MSG).
Food additives are added to enhance the flavour, appearance and shelf life of foods. Your body cannot tell the difference between natural food chemicals and artificial food chemicals in processed foods. MSG is popular flavour enhancer used in savoury snack foods, soups, sauces and Asian foods. Foods rich in glutamates or the natural chemical include cheese, tomatoes and mushrooms. Those who are sensitive to the chemical glutamate may react equally to high intakes of MSG and natural glutamate.

Coeliac disease
Coeliac disease is caused by an immune reaction to gluten, a protein found in certain grains including wheat, barley and rye. The condition involves inflammation and damage to the lining of the small intestine, which can impair nutrient absorption.
Symptoms can include mouth ulcers, fatigue, bloating, cramps, diarrhoea and skin rash. Some people have no symptoms at all while others develop health conditions due to nutrient deficiencies such as anaemia and osteoporosis.
Blood tests are usually performed to detect antibodies, followed by an endoscopy and small bowel biopsy. However, for these tests to be reliable you have to include gluten in your diet regularly. Tests can become negative within a few weeks with gluten avoidance.
Some people experience symptoms after consuming gluten without having coeliac disease – such people are described as ‘non-coeliac gluten intolerant’ and they feel better when they avoid gluten. The current treatment for coeliac disease is life-long avoidance of gluten.

Irritable bowel syndrome (IBS)
IBS is a common condition characterised by gastrointestinal symptoms. The most common symptoms include lower abdominal pain, bloating, wind, diarrhoea and constipation.
A large number of dietary triggers have been associated with IBS, including fatty foods, alcohol and caffeine. Recent research conducted by Monash University’s Department of Medicine focused on the dietary sugars fermentable oligosaccharides, di-saccharides, monosaccharides and polyols (FODMAPS).
In a recent newspaper article, senior lecturer at Monash University Dr Sue Shepherd says that some sensitive people experience ferment in the gut, which causes bloating and wind. She also cites a 2005 study at Monash University that found IBS symptoms were improved by avoiding or reducing foods high in these saccharides. Examples include wheat, rye, cow’s milk, apples, pears, stone fruit, watermelon, cabbage, broccoli, onions, mushrooms and legumes.

Elimination diets
Unlike allergies there are no skin or blood tests that can help diagnose food intolerances. It is also not possible to tell from a person’s symptoms to which chemicals they are sensitive. Food intolerances are usually diagnosed via an elimination diet where a low chemical diet is followed for a period of time to allow symptoms to reduce before challenge foods are reintroduced one at a time.
The Allergy Unit at the Royal Prince Alfred Hospital has produced elimination diet guidelines, which are available to the public.
So it’s important to investigate whether feeling queasy or bloated after a meal is the result of a mild intolerance or full-blown allergy. You may be surprised to learn that an allergy you’ve suffered from since childhood is merely an intolerance that may allow you to enjoy small portions from time to time – it’s simply a matter of separating allergy from intolerance.