Over the last 10 years or so, the occurrence of allergy in general has dramatically increased, to the point where the World Health Organisation (WHO) has declared it to be one of the epidemics of the 21st century. Although we know that there has been an increased prevalence in developed countries, we also believe that increased awareness will provide better knowledge and understanding of allergy symptoms.

What is food allergy?

A true allergy is a reproducible reaction to a food that has an immunological basis. The term “allergy” is derived from the Greek, allon argon, which means “to react differently” (which is what happens when people are allergic). Food allergy is an over-reaction of the body’s immune system to a specific component in a food, usually the protein component, whereby a natural, normally harmless and tolerated food is perceived as a dangerous invader and induces an over-reaction. In most individuals, the immune system in the digestive tract fights against harmful organisms, while recognising that foods are harmless. This ability to differentiate is an expression of oral tolerance to foods. In a minority of people, the finely balanced mechanism does not work optimally. Their immune defences over-respond, resulting in sensitisation and ultimately, with repeated exposure, a development of an allergy to the food in question. The symptoms range from gastrointestinal (eg diarrhoea and vomiting) and dermatological (eczema and urticaria) to respiratory (eg asthma and rhinitis) symptoms.

What is food intolerance?

Food intolerance can be due to enzyme deficiencies, and other mechanisms that mimic true allergic reactions. Food intolerance is referred to as a non-allergic food hypersensitivity and is a reproducible adverse reaction to food. It should not be confused with a true food allergy, because it is not caused by an immune reaction but by a range of other factors, such as an enzyme deficiency. Intolerances may also result from food poisoning with pathogenic bacteria or can be due to metabolites formed in the body that induce an intolerance reaction such as Chinese restaurant syndrome. (Symptoms are usually more gastrointestinal, for example, with lactose intolerance.) Lactose intolerance is the inability to digest significant amounts of lactose, the major sugar found in milk. Lactose intolerance is caused by a shortage of the enzyme lactase, which is produced by cells that line the small intestine. People who do not have enough lactase to digest the amount of lactose they consume may experience symptoms such as nausea, bloating, gas and diarrhoea.

Which foods can cause an allergic reaction?

Very simply, an allergy (or an allergic disease) is a hypersensitive over-reaction of the body to foreign matter in the environment. An allergic reaction is almost exclusively caused by a protein when a specific sequence of amino acids in a protein is recognised by the antibody Immunoglobulin E (Ig E); this then triggers the physiological chain of actions that set off an allergic response.

What are the most common types of food that cause an allergic reaction?

Although an individual could be allergic to any food, such as fruits, vegetables and meats, there are foods that account for 90 per cent of all food-allergic reactions:

• Cereals containing gluten (i.e. wheat, rye, barley, oats, spelt, kamut or their hybridised strains)
• Crustaceans
• Molluscs
• Eggs
• Fish
• Peanuts
• Soybeans
• Milk
• Nuts (i.e. almond, hazelnut, walnut, cashew, pecan nut, Brazil nut, pistachio nut, Macadamia nut and Queensland nut)
• Lupin
• Celery
• Sesame
• Mustard

Who is ‘at risk’ of developing an allergy?

Many factors can influence susceptibility to allergy symptoms. When we say at risk, we refer to young infants who are particularly susceptible to food allergies, possibly because of the immaturity of their digestive tract and/or immune system. Genetic predisposition inherited from the parents, plays a major role in the development of atopic disease, however, simple mathematical calculations demonstrate that comparable absolute numbers of those considered at high and low risk of allergies will develop symptoms during their life. Statistics show that when neither parent is allergic, the risk for a child to develop an allergy is about 15 per cent. This doubles when one parent is allergic, is quadrupled if both parents are allergic and is even higher when both parents present the same allergy symptoms. The first 6 months of life are the dangerous period for sensitisation to food allergens. Foods should be introduced one at a time in small amounts.

Allergy prevention

Primary prevention is to induce immunological oral intolerance in early infancy. In practice, two different approaches are needed, depending on the immune status of the infant; whether he or she has previously come into contact with and reacted to an allergen or not. Primary prevention attempts to prevent the initial onset of sensitisation and symptoms in subjects at-risk but as yet unsensitised. One of the main aims of primary prevention of food allergy is to induce immunological oral tolerance to food proteins in early infancy, mainly to cows’ milk proteins. Secondary prevention targets individuals already sensitised to keep them symptom free, (this refers to the treatment of an already allergic individual). This includes preventing further allergic disease in an infant who is already sensitised to a specific allergen, e.g. pollen, dust mite, etc.

Source: Nestle UK