Food allergies and intolerance

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18 Food allergies and intolerance

Greg Whelan, Patrick Allen

Case

A male aged 16 years presents complaining of abdominal bloating and diarrhoea for 1 month. This commenced following an outbreak of what was described as viral gastroenteritis in his boarding school. All the other pupils have completely recovered.

His symptoms occur soon after eating or drinking. Specific inquiry reveals that milk or milk products appear to exacerbate his symptoms of bloating and diarrhoea. He has lost approximately 2 kg weight.

Physical examination was normal.

A lactose tolerance test was positive. This was confirmed by a positive lactose breath hydrogen test.

Following a consultation with a dietician he commenced on a lactose-free diet using soy products to substitute for milk. He has remained symptom-free.

Introduction

Many patients who present with gastrointestinal symptoms—particularly abdominal pain, diarrhoea and abdominal distension—complain of food-induced symptoms and believe that they are ‘allergic to food’. In some of these individuals there is food intolerance secondary to an underlying disease such as lactose malabsorption. However, the majority of patients have a functional gastrointestinal disorder, in which the mechanism of the perceived food intolerance is obscure. Only a minority of the apparently food-intolerant individuals will subsequently be found to be truly reacting adversely to components of the food they eat and rarely will this reaction be of an immunological (allergic) nature.

Adverse food reaction can be broadly based into two categories. The first category is immunologically mediated adverse reactions to foods. These particular reactions are unrelated to any physiological effect of the food or food additive, and are mediated by immunoglobulin E (IgE) antibodies and others result from non-IgE-mediated mechanisms.

The second category is food intolerance. These reactions include any adverse physiological response to a food or food additive that is not immunologically mediated, such as lactose intolerance or pharmacologically related adverse food reactions.

The mainstay of management of food allergies and adverse reactions remains focused on avoidance of the allergenic or reactive foods. There have been recent multiple advances to various therapies that may eventually complement or even replace the main therapeutic approach, which is food avoidance.

A Clinical Approach

History and physical examination

The relationship of the gastrointestinal symptoms to meals needs to be determined. In true food allergy this commonly occurs soon after ingestion. Excessive bloating and diarrhoea suggests lactose intolerance. In functional gastrointestinal disorders, symptoms after meals are common but symptoms between meals are also frequent and often no food can be consistently blamed. The specific symptoms of irritable bowel syndrome should be sought (Ch 7). Individuals may react to the nutrients in food, such as protein, carbohydrate, fat, vitamins or minerals or to food additives. Foods that commonly cause reactions are summarised in Table 18.1.

Table 18.1 Main foods that commonly cause gastrointestinal disturbances

Food type Common examples of trigger foods
Cereal grains Wheat
Dairy products Milk, cheese
Fruit Citrus Fruit
Vegetables Onions, capsicum
Miscellaneous foods Coffee, eggs, chocolate

A physical examination is generally unhelpful, unless the patient is currently experiencing symptoms. Occasionally skin rashes or signs of asthma are detected. It may be helpful in excluding other disorders.

There are multiple approaches to elicit a history from individuals with adverse food reactions that are possibly due to an allergen.

The suggested approach is to elicit three main elements from the history:

1. symptoms associated with adverse food reaction such as nausea, bloating, vomiting, itch;
2. possible reactive or triggering foods—peanuts, for example;
3. possible contributing factors that may have exacerbated the adverse reaction such as associated with concomitant drug therapy or associated with exercise.

Note that allergic reactions to food have the potential for serious, even fatal, outcomes. Thus the highest priority is to elicit the symptoms of the allergic reaction if they can be identified.

What are the symptoms involved with the allergic reaction?

These can include the following common presentations:

• systemic symptoms—palpitations, dizziness, fainting and collapse;
• gastrointestinal symptoms—nausea, vomiting, diarrhoea and cramping abdominal pains;
• dermatological—urticaria, angio-oedema, flushing, swelling or itching a few minutes after food;
• respiratory symptoms—stridor, wheeze, cough and dyspnoea.

What was the onset of symptoms like? Was the onset acute or subacute?

How rapidly did the symptoms occur after the ingestion of the allergen? IgE allergic reactions can typically occur within minutes, whereas non-IgE (cell-mediated) reactions tend to develop more gradually over hours to days.

How severe was the allergic reaction on this occasion?

All of the symptoms experienced should be documented and their severity explored. Did the patient require hospital admission with severe cardiorespiratory symptoms? If this is the case, this is usually an acute IgE-mediated reaction.

Has this reaction occurred in the past? If so what was the severity grade then?

If the patient had anaphylaxis requiring intramuscular adrenaline and treatment in an intensive care unit, this is likely to be a severe IgE-mediated reaction. The patient’s medical records should be requested and reviewed to confirm symptoms such as wheezing, flushing, stridor and collapse as patients may not be fully aware of these events.

Identification of Food Allergens

It is important to accurately document the potential food allergens and their previous effects and reactions. Such documentation includes the following points:

• Develop a list of foods that may have caused the symptoms. Eggs, nuts and seafood are the usual suspects.
• Discuss the minimum quantity of food required to produce the symptoms.
• Explore the preparation of the relevant foods (raw, cooked, contaminated with another food additive, spices and so on).
• Explore the characteristic symptoms that the patient experiences on exposure to the relevant food.

Identification of contributing factors

The questions below are potentially less helpful in identifying the offending allergen, but they may also provide the clinician with some additional information regarding the exacerbating factors to the allergic response:

• Did the patient receive any concurrent medications at the time of the allergic reaction? It has been reported that alcohol or anti-inflammatory agents may exacerbate the allergic reaction.
• Was the patient involved in any physical exertion before the reaction? Some reactions may be severe after physical exercise.

Physical examination in the emergency department

The initial examination to a patient presenting to an emergency department is to assess the severity of the condition and includes careful assessment of:

AAirway

BBreathing

CCirculation.

To assess signs of severe anaphylaxis it is important to observe for cardiorespiratory compromise and dermatological manifestations, which include the following:

• acute respiratory complications: bronchospasm, stridor, wheeze, cyanosis;
• acute cardiovascular complications: tachycardia, hypotension, delayed capillary refill time, drowsiness;
• acute dermatological signs: angio-oedema, urticaria.

If these features are present, immediate treatment should be instituted; see the sections on management below.

The majority of food allergies present subacutely or chronically, so the preferred approach is to identify any possible manifestations of their allergy, for example dermatological symptoms, along with a detailed history as above. There are various symptoms of chronic diseases where a food allergy may be responsible; for example, atopic dermatitis has been associated in approximately 40% of infants or children with moderate to severe atopic disease.

Investigations

Appropriate investigations may be needed to exclude other relevant diseases such as coeliac disease and inflammatory bowel disease or to confirm a suspicion of lactose intolerance. This is particularly important if there is evidence of weight loss or gastrointestinal tract bleeding. The specific features of immunologically mediated adverse food reactions and food intolerance are discussed below.

Pathophysiology

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