Can't eat wheat products? Feel a bit off after drinking milk? Do additives bring you out in a rash? For some people, food allergies or intolerances make healthy eating a real challenge. Dietitian, Matt O'Neill puts the record straight about adverse reactions to food and shares some good advice fitness professionals should give.

The most common misconception about food allergies is that they are quite common. Sometimes its claimed humans weren't meant to eat wheat products or drink cows milk. Yet the vast majority of the population thrives on these nutritious foods. It's more the case that a small percentage of people experience bad reactions and have to be careful of what they eat. From 1-4% of the population are genuine food allergy sufferers and perhaps up to 20% experience some degree of food intolerance. And there is an important difference between an allergy and intolerance.

Food allergy

Food allergies can be severe enough to cause death. For example, an adverse reaction to even the smallest trace of peanuts in a meal, can cause anaphylactic shock, which is a sudden and potentially fatal allergic reaction. Initial symptoms usually involve extreme swelling of the mouth and throat, then the respiratory and circulatory systems can shut down.

The common culprits for allergies include peanuts and other nuts, fish, shellfish, egg white and cows milk protein. These foods often have to be avoided for life and sufferers should never assume that a substance they haven't tried for a while will be safe to eat. Allergy suffers are often vigilant label readers and quickly become aware of foods to be avoided.

Characteristics of food allergies

• Uncommon
• Generally experienced for life
• Generally one or two specific foods
• React to the smallest amount in foods
• Severe life threatening reactions
• Easier to diagnose because usually acute reaction to a single food

These don't tend to be as severe as a genuine food allergy, rather they cause a range of adverse reactions in different people including an itchy skin rash, headache, irritability, hyperactivity, bowel pain or respiratory problems.

Food intolerances are generally dose-related which means that some people may be intolerant to certain substances in food but never eat enough to trigger a reaction. People who know they are intolerant therefore often set themselves limits as to how much of certain foods they can eat.

Characteristics of food intolerances

• Common
• May grow out of it
• May react to a chemical or ingredient present in a range of foods
• Severity of a reaction is dose-related
• Range of responses from mild irritation to severe discomfort
• Harder to diagnose because many foods many contribute to the reaction

Lactose - a small percentage of people are unable to properly digest the simple carbohydrate in milk due to a lack of the enzyme lactase in the small intestine. Lactose makes its way to the large intestine where it reacts with the bacteria present, and causes and range of symptoms including diarrhoea, flatulence and pain.

If you are lactose intolerant, you may be able to stay below your threshold for a reaction by limiting milk. Cheese and yoghurt, in which the lactose is fermented or used up by the bacteria in production have much less lactose.

Gluten - similarly, some people are unable to digest the protein in wheat, so they need to choose wheat-free substitutes like rice flour and corn starch. People who suffer celiac disease (the condition of gluten intolerance) gain some assistance from the increasing number of wheat-free foods on supermarket shelves.

Food additives -- one example, is sulphur dioxide. This chemical is released by sulphite preservatives often added to dried fruit, and can cause breathing difficulties such as wheezing, or trigger attacks in people who have asthma.

Some naturally occurring substances can cause just as many problems as food additives. Salicylates (found in acidic fruit), amines (in cheese, tomato and chocolate, among other foods) and glutamates (found in soy sauce and mushrooms, for example) can all have an adverse affect on people who are sensitive to these.

The best advice

If you think you react badly to certain foods or your clients report adverse reactions, its important not to try and self-diagnose or treat yourself. The potential causes are complicated and incorrectly eliminating foods can end up restricting your diet unnecessarily.

Speak with a doctor, or a dietitian who specialises in adverse food reactions. Their knowledge of related medical issues and food combinations can take some of the guesswork out of building a diet to beat bad reactions.

(C) Matt O'Neill 2003

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Useful links:

FoodStandards.gov.uk - More on specific food allergies & intolerances