The articles are definitely NOT for any public use whatever, nor intended in any way to be taken as advice for any medical or health condition.
One of the areas of clinical nutrition which family physicians find most vexing is the patient with a possible food allergy. A wide range of symptoms have been listed as possible consequences of food allergy - many of them common and non-specific. Often the situation is compounded by the fact that the possibility of food allergy has been raised by the patient themselves or some alternative therapist. With little or no training in this subject, what is the poor family physician to do?
The first thing for family physicians to realise about food allergy is that it consists of two distinct categories.
In the first category are those conditions where there is a clear cut, immunologically mediated allergic reaction to a specific food allergen. A good example of this condition is the patient with immediate hypersensitivity to a specific food, such as crustaceous seafood. Typical symptoms might be rash, swollen lips and respiratory distress, and the time frame is usually short - half an hour or less after eating the food. This reaction is consistently reproducible, associated with diagnostic changes in immunoglobin levels related to the particular allergen and relatively uncommon.
Less dramatic but still within the clear cut food allergic category are `true' cows milk allergy, most often seen in children, where it can produce a variety of symptoms including diarrhoea and abdominal pain, and coeliac disease. In the latter case, for example, the immunological basis is demonstrable by the finding of elevated gliadin antibody in the patient's serum. (For more information on coeliac disease, there are a number of Internet resources available )
However, this category of food allergy only accounts for a small proportion of patients' concerns in this area. The larger portion is taken up with the much vaguer notion that individual foods or food groups might be responsible for a whole host of symptoms and conditions, ranging from asthma and eczema to tiredness, recurrent mouth ulcers, headaches and pruritus. Initially, these sorts of claims, often accompanied by vivid anecdotal experience, were strongly rejected by the medical profession as being unscientific and the realm of alternative medicine.
In fact the belief that food allergy is both common and capable of causing a great variety of symptoms has been increasingly adopted as a tenet of alternative medical practice since the 1980s. A branch of allergy practice called environmental medicine has sprung up to incorporate this free ranging concept of foods together with many other potentially hostile environmental substances as being important causes of disease. Some practitioners of this environmental medicine employ a number of diagnostic tests, such as white cell reactivity, which are not widely accepted within orthodox medicine.
Yet, after beginning with a fairly negative response to this sort of concept of food allergy, orthodox medicine has gradually acknowledged a steadily growing body of evidence which demonstrates that foods can indeed some of these symptoms. For example, rigorously conducted studies of children with asthma, as well as those with eczema and recurrent headaches, have shown that a significant proportion of such children have a reproducible positive response to elimination of certain foods, and relapse on reintroduction of those foods. In some cases the reintroduction was in double-blinded capsule form.
It has become apparent that there is a second and distinct form of food allergy, which is actually not an allergy at all in the classical sense of a well defined immunological response. Instead, these reactions to foods have been labelled food sensitivity. Some people appear to react adversely to certain foods, by a mechanism which is not clearly understood, but which may well account for many of the anecdotal food-symptom connections that patients have been reporting to us all these years.
Such reactions do not necessarily appear immediately after consuming the offending food. Indeed they may not occur by any means on every occasion that the food is eaten. In some cases the reaction will be dose related, and hence will not be seen until a threshold total dose of food has been consumed. In other cases, the person's overall health may affect their reactivity, so that they may be more sensitive when generally run down etc. This category of `food allergy' is less likely to follow any familial pattern than the classical immune-based food allergy.
Even though orthodox medicine has become more accepting of this diagnosis, there is still dispute as to which foods are most commonly implicated. The most common ones so far reported in the published literature have been dairy produce, eggs, wheat, nuts and some food additives, such as certain colouring compounds. But in other research conducted in Australia it was found that naturally occurring salicylates were more common culprits. They have been linked with a range of non-specific symptoms, such as headaches and recurrent mouth ulcers (salicylates are found in a diverse list of foods, including many fruits).
Bearing this background in mind, the following is a practical stepped approach which can be applied by any family physician in dealing with possible food allergy:
Even so, try to pin the history down to specifics: what foods cause what symptoms? What is the time-dose relationship? Are there any other salient aspects of the patient's general condition?
A modest set of laboratory tests may be helpful, directed as much towards eliminating other systemic causes of the patient's symptoms as at identifying food allergic causes (e.g. FBC, LFT etc.) Food IGE RAST testing is often performed, but it still remains unclear what objective value this has, both for negative and positive results. The family physician needs to avoid putting too much wait on diagnostic tests in the diagnosis of food allergy.
If the above approach does not work, the time may then be ripe to proceed to the next step of an diagnostic elimination diet. This will be dealt with in the following article.
