Food Allergy and Food Intolerance… what is the difference.
One in five individuals in Australia have at least one allergy, which places Australia with one of the highest prevalence’s of allergy amongst the developed world (1). If the present trend continues it is estimated that there will be a 70% increase in the number of Australians with allergies by 2050, which correlates to 7.7 million people (1).
The high and ever increasing prevalence of food allergy and atopic disease has researchers identifying genetic predisposition as a risk factor, where in children with neither parent having an allergy, the child will have a 20% chance of having one allergy disorder (2). If one parent has an allergy disorder the risk increases to ≈ 40%. If both parents have allergy disorders then the risk increases to 60 – 70%. In addition to genetics some studies reveal the importance of the impact of environmental influences (2).
Researches from the John Hopkins Children Centre believe there is a trend toward more severe and more persistent allergies (3). However it should be noted that the severity of allergy presentation in a family history is not a good predictive guide as to how sensitive a child may be (4). In many cases when the presentation of allergy or food intolerance in the parent is only mild the possibility of allergy or food intolerance being related to a child’s symptoms can be overlooked (4).
The allergen pathway commences before the child is born, with allergens crossing the placenta, programming the immune system down the allergy pathway (4). This impact commences about halfway through the pregnancy, which is the time a mother could start focusing on minimising allergen exposure via modifying the maternal diet and minimising environmental factors (4).
The modification of the maternal diet encompasses a varied diet based on the Australian Dietary Guidelines (4). It discourages bingeing on any food in the second half of the pregnancy and during breastfeeding (4). There should be the total avoidance of egg, seed, peanut and nut (from the household) (4). There are precautions to take with respect to milk and dairy foods, and also fish and other seafood, and a minimisation of one’s intake of soybeans and other legumes (4). With respect to meats, allergies can occur, with pork allergy tending to be more likely to occur when eaten with fat (4).
It is recommended that lean meats are consumed. Wheat, oats, barley and buckwheat can all cause allergy and tend to only cause symptoms in highly allergic infants (4). In relation to vegetables, potato allergy is commonly seen in the highly allergic child, however in general there is no reason to modify vegetable intake during pregnancy (4). This may, however, be necessary during breastfeeding as some infants may react to tomato and spicy foods (5). Of the fruits the avoidance of the citrus family is recommended, with the reactions occurring to fruit often being related to a food intolerance rather than an allergy (5). Kiwifruit is the most allergenic fruit with the possibility of allergy development in the highly sensitive child (4).
The environmental measures include the total avoidance of cigarette smoke, ensuring houses are well ventilated, particularly kitchens where there are gas cook tops, and taking dust mite allergen precautions and pet precautions, particularly with respect to cats, rabbits, guineas pigs and mice (4). There should be total latex avoidance, in particular powdered latex products that cause the allergy to develop (4).
The allergen pathway highlights the possibility of the presentation of allergy related symptoms early in life, with researchers identifying that 2.2% – 5.5% of infants have food hypersensitivity during the first year of life (5). In the presentation of allergy in children we usually find that they are allergic to two or three different foods, with the most common being peanut, egg, milk, other nuts, seafood and sesame. Wheat, soy and rice can also cause allergies (5).
We should also consider the possibility of food intolerances. There is often confusion about the difference between allergy and intolerance and the terms are sometimes used in place of one another. There is a difference between food allergy and intolerance both in the types of foods and the way they affect individuals.
The immunological basis to Food Allergy
In the normal process of digestion food proteins are broken down in to smaller proteins (peptides) by enzymes in the stomach and the small intestine (7). These smaller particles are prevented from entering the tissues of the small intestine by physiological and immunological barriers (7).
However, on occasions, small proteins (peptides) are absorbed through the gastrointestinal tract, which initiates an immunological response (7). Whether this initiates an allergic (Ig-E mediated) or intolerant response (Non Ig-E mediated) is dependent on the genetics of the individual, the characteristics of the food protein and the microenvironment. It is the interaction of these components, which leads to the development of a Food Allergy or Food Intolerance (7).
The classic allergic response manifest as urticaria (hives), angioedema and anaphylaxis; the more delayed allergic response may manifest as inflammation in the colon or skin or enterocolitis or eczema respectively (7).
Classic IgE – immunological mediated allergic response…. How does it start?
The food protein enters the body via the gut or lung mucosa. Once inside the tissue, these proteins are then engulfed by specialised cells (deneretic cells) (7). This then stimulates B cells to produce Th2 cells (7) this results in a stimulation of cells, which results in the production of antibodies. These antibodies bind to mast cells in the tissue or basophils in the blood and stay in the tissue for months. This process is called sensitization (7). These antibodies are known as specific IgE antibodies. On a subsequent occasion when the body is then exposed to this food protein the protein binds to the antibody. This results in the breakdown of these cells and the subsequent release of histamine, prostaglandins, leukotrienes, platelet activation factors and bradikynin (7). These chemicals result in vascular dilation and hyperpermeability, which attract cells into the tissue, which results in inflammation (7). Skin Prick Tests (SPT) and Radioallergosorbent Test (RAST) are used to diagnose Ig E immune mediated food allergy.
Non – IgE – Immune mediated Food Allergy
The mechanism to non-IgE mediated food intolerant reaction is not always clear. There have been several research studies, which have investigated the Immunological basis of gastrointestinal non-IgE allergies. These have clearly identified the involvement of T- cells (Th1 and? Th2) and cells such as oeosinophils (7). The mechanism encompasses the initial exposure of the protein to the tissue, which results in the sensitization of the T- cell (7). Then, the subsequent exposure results in the release of inflammatory chemicals (cytokines), which lead to chronic inflammation (7). The presentation of non-immune mediated food allergy can present at all ages.
There are diagnostic difficulties associated with the diagnosis of non-IgE mediated food allergies. The diagnostic tools include biopsy and patch testing (7). Patch testing has a role in eosinophillic oesophagitis and atopic dermatitis, although we sometimes use it to help identify foods that may be causing bowel disturbance. When the food is placed in contact with the skin, the specialized cells in the skin pick up the food proteins and present it to the immune system. If the individual has sensitivity to that food, they will react with inflammation at the site of the food over the next 2-3 days. This gives us a window to what is happening in the gastrointestinal tract with foods.
Non allergic food hypersensitivity / food intolerance
A non-allergic food hypersensitivity is usually characterised by a delayed reaction, which can occur hours or even days after eating (7). The sensitivity to certain foods is defined as the inability to properly process and fully digest certain foods, leading to chronic symptoms. A food sensitivity / intolerance does not involve the immune system though rather involves the stimulation of nerve endings in tissues by a chemical component which may be naturally occurring, an additive, or a combination (6). These include amines, salicylates, glutamates, preservatives and colours. Symptoms of food intolerance are extensive and variable. They can be very similar to those of an allergic response. Symptoms of allergic reaction are usually sudden, while intolerance response may sometimes occur straight after ingesting a problem food or have a delayed response. Symptoms may take 12-24 hours to develop. The severity of symptoms can also depend on the quantity of the problem food ingested. They may not occur until a threshold amount is ingested.
Where to from here?
A child that continually screams when being breast fed, has unsettled sleep patterns, wakes moaning with writhing, has loose stools, is colicky, has slow weight gain, reflux, eczema, nappy rash, or displays irritable, impulsive or overactive behaviour, should prompt us to consider the possibility of food allergy/food intolerance.
An experienced dietician, while awaiting an appointment with an allergist, can undertake the initial investigation of a possible food allergy/food intolerance. Once identified then an appropriate management plan can be established. Continual guidance and support are key factors in the management of these conditions, through what can be a challenging time for children and their families.
1. Australasian Society of Clinical Immunology and Allergy, November 2007, Economic Impact of Allergies.
2. Professor Mimi Tang, SBS, TV Allergy program, October 2007, Allergic Reaction: Children and their allergies.
3. Dr Velencia Soutter, December 2007, email communication.
4. Royal Prince Alfred Allergy Resources, Food Allergy Prevention.
5. Scott H. Sicherer, MD, Donald Y.M. Leung, MD, PhD, June 2007, Food allergy, anaphylaxis, dermatology and drug allergy, Journal of Clinical Immunology, Advances in Asthma, Allergy and Immunology Series 2007, pp 1462 1469.
6. Dr Robert Loblay, SBS, TV Allergy program, October 2007, Allergic Reaction: Children and their allergies 7. Isabel Skypala and Carina Venter, Food Hypersensitivity, Diagnosing and Managing Food Allergies and Intolerances, Blackwell Publishing 2009.