So which foods are most likely to trigger symptoms of food intolerance such as gut problems, headaches, rashes, hives or fatigue?
If you guessed wheat or dairy you'd be right - but only to a point. For around 50 to 70 per cent of people with food intolerance the triggers are natural plant chemicals often found in foods that are hard to pick a fight with - like fresh vegetables and fruit. The most common culprits are salicylates found in tomatoes, blueberries, almonds, pineapple and herbs and spices, for instance. Other natural chemicals are amines found in avocado and bananas, and glutamate found in mushrooms,
These are all healthy foods but for some sensitive people - around 10 per cent of us - the natural chemicals that help give them the flavours we love can also provoke a reaction, explains Dr Anne Swain, head dietitian at the Allergy Unit at Sydney's Royal Prince Alfred Hospital. These same plant chemicals are often in more processed foods too - amines, for instance, a product of fermentation and protein breakdown - also turn up in foods like cheese, chocolate, yeast extract and wine.
"The tastier a food is, the richer it's likely to be in these food chemicals," she adds. "I often think of food intolerance as a disease of affluence because we can often afford more naturally flavoursome foods," she says.
That doesn't mean that food additives like preservatives, colourings and flavourings aren't triggers for food intolerance too but the problem is just as likely to be a naturally occurring chemical - although people who react to natural food chemicals may often react to additives too, she adds.
But we do like to blame wheat and dairy.
"Dietitians say more people are going on wheat free or dairy free diets but these foods aren't always the real triggers," says Anne Swain. "People may feel better when they avoid these foods but it may be because when they avoid them the change of diet also cuts back on other foods that happen to contain chemicals like salicylates and amines."
If you're avoiding dairy then you're also avoiding amines in cheese - but it may not be dairy food itself that's the problem, but amines. People who avoid wheat also avoid pizza, pasta and toast but in avoiding them they're also reducing foods that often accompany them and which may contain salicylates, amines or glutamate - like tomatoes and cheese on pasta and pizza or yeast spread on toast.
The lesson from this, says Swain, is that if you think certain foods are causing real problems, it's best to try and identify the real culprit rather than unnecessarily avoid foods - such as wholegrain bread or yoghurt for instance - that have benefits.
"It's also important to rule out other conditions that could be causing the symptoms too - symptoms like gut problems, rashes, constipation, headache and fatigue can have a lot of other causes," she points out.
Still, nailing down the true trigger of a food intolerance isn't easy. While there are tests that can help diagnose food allergies, there's no simple test to find the culprits in food intolerance.
Unlike food allergy which is caused by the immune system overreacting to certain proteins in foods, food intolerance is a very different problem triggered when some food chemicals irritate nerve endings in different parts of the body, Anne Swain explains.
"People with food intolerances probably have a genetic predisposition too but the intolerance may be amplified at any age by hormonal changes, stress or an infection that can change the way the body reacts to food chemicals," she says.
"The best way to find the triggers is with a diagnostic elimination diet which avoids all suspect foods for three to four weeks, followed by a process of introducing foods gradually over a period of weeks to see which ones provoke a reaction.
"Fully complying with this diet can be hard at times which may be why many people opt for tests that are simpler but aren't reliable such as IgG food antibody testing, a blood test. It's an expensive test and a lot of people with suspected food intolerance do it but it tends to show what you've eaten recently - not what you're sensitive to."
But it's worth sticking with the elimination diet, she adds - it's helped many people identify their problem foods and end up successfully managing their symptoms.
For more information about food intolerance see the RPA Allergy Unit website
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