Updated 24 May 2017

Understanding food intolerance

Calling food intolerance a scientific void ignores existing scientific evidence, claims Food Intolerance Network co-founder Dr Howard Dengate.

Calling food intolerance a scientific void ignores existing scientific evidence, claims Food Intolerance Network co-founder Dr Howard Dengate.

While there is a need for more clinical studies to be published, the risk is that the food industry will miss out on opportunities for new markets if they avoid the issue.

The confusion about food intolerance can be clarified by an understanding of three key concepts, which would allow consumers and the food industry to move forward.

Firstly, it is essential to understand the differences between food allergy and food intolerance.

True food allergy is comparatively rare, affecting perhaps eight percent of children and four percent of adults. It is a quick immune system-mediated reaction to the proteins in a few foods such as milk or nuts and can be confirmed by a laboratory test.

Food intolerance, on the other hand, is common, reactions are dose-related and there's typically a delayed response to artificial or natural chemicals in foods. Many foods may be involved with a bewildering range of symptoms. As there are no scientifically proven laboratory tests, diagnosis is through the use of an elimination diet with challenges.

Elimination diet effective
The Food Intolerance Network considers that the most scientifically valid and effective diet is a low-chemical elimination diet based on Feingold and developed further by researchers at the Royal Prince Alfred Hospital in Sydney, Australia.

This diet uses foods low in salicylates, amines and natural flavour enhancers and avoids some fifty additives known to cause problems. Unequivocal challenges can then be achieved against a stable baseline.

The second key concept regarding food intolerance is that most consumers who are affected by food chemicals are unaware of the cause of their symptoms because of the 30-minute rule.

Research shows that consumers will make the connection between what they eat and how they feel only if the reaction occurs within 30 minutes. As true food allergies such as a reaction to peanuts are generally a quick response, they are relatively easy to identify.

However, most intolerance reactions can be delayed for hours, even days, or build up slowly. If a child has a bad day on Monday, few parents think, that's because we had takeaways on the weekend. Yet, that's the way it happens.

In a study of an entire class of six-year-olds in the UK in 2003, nearly sixty percent of parents reported that their children's behaviour and sleeping improved after two weeks on a diet avoiding 39 common additives. Most of these parents were previously unaware of the effects of additives on their children.

Thirdly, the manifestations of food intolerance can extend into every area of health and behaviour, which is what makes research so difficult.

Five categories of symptoms
There are five main categories of food intolerance symptoms. It is common to find that members of a family can all be affected in different ways:

  • hives, eczema, other itchy skin rashes;
  • stuffy or runny nose, asthma, frequent colds or ear infections;
  • frequent mouth ulcers, reflux, bloating, stomach aches, constipation and/or diarrhoea, bedwetting, urinary urgency;
  • migraines or headaches;
  • impairment of concentration, anxiety, depression, lethargy, irritability, restlessness, oppositional defiance, difficulty falling asleep, night waking, restless legs.

Consumers often have no idea how much better they or their children can feel until they try the elimination diet. In a typical experience, after starting on their new food programme, one mother wrote about her son: "He has been a lot calmer the last few days and polite and wanting to help - it's been a real change."

Sales growth in UK
As a result of consumer concerns, the UK free-from food market, including dairy-, gluten- and wheat-free products, has already enjoyed sales growth of over 300 percent since 2000 and is set to double, according to market analyst Mintel.

Consumers with food intolerance are also likely to choose products that are free from the following additives: artificial colours, natural colour annatto (E160b), sorbates, benzoates, sulphites, propionates, nitrates, nitrites, synthetic antioxidants, MSG and the nucleotide group of flavour enhancers.

As well, current plans for genetically modified crops with higher salicylate levels will create huge problems for food-intolerant consumers, in the same way that the widespread use of vacuum-packed meat with higher levels of biogenic amines is leading us to seek independent butchers who sell fresher meat.

Scientific references concerning food intolerance at show that there is plenty of science, but not enough knowledge of this growing problem. Correctly understanding the three concepts above will allow regulators and industry to better grapple with the issues. - (Decision News Media, August 2006)

Read more:
What is food intolerance?
Allergic to food additives?


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Dr Morris is the Principal Allergist at the Cape Town and Johannesburg Allergy Clinics with postgraduate diplomas in Allergology, Dermatology, Paediatrics and Family Medicine dealing with both adult and childhood allergies.

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