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The rise of food allergies

Evidence-based medicine

Gerry Morrow

Monday, 15 April 2019

AdobeStock_122922026_allergy.jpgFood allergies are on this rise, with rates as high as 10% being reported. A food allergy is an adverse immune-mediated response, when a person is exposed to specific food allergen, usually by ingestion.

Immunoglobulin (Ig)E-mediated food allergy follows exposure and sensitisation to trigger food allergens with the development of serum-specific IgE antibody. It produces immediate symptoms, which may affect multiple organs.

Non-IgE-mediated food allergy involves cell-mediated mechanisms, which tend to occur in young children and presents with symptoms such as vomiting, diarrhoea, abdominal cramps, colic, and possible faltering growth.

IgE and non-IgE-mediated food allergy may present as cows' milk protein allergy, eosinophilic oesophagitis, or eosinophilic gastroenteritis.

The risk in food allergy prevalence in childhood has been ascribed to environmental factors such as qualitative and quantitative changes in the infant microbiome.

Food intolerances are non-immune adverse reactions to foods and/or food additives which are distinct from food allergy. They often present non-specifically with gastrointestinal symptoms, headache, fatigue, and musculoskeletal symptoms. Typically, there is a delay in symptom onset and a prolonged symptomatic phase. They may overlap with conditions, such as irritable bowel syndrome or fibromyalgia. The cause is unknown, but they may be due to enzyme deficiencies or pharmacological reactions to chemicals such as caffeine.

Allergy may develop to almost any food, but common food allergens include, cows' milk, hen's eggs, peanuts and other legumes, tree nuts (such as walnut, almond and Brazil nuts) and crustacean shellfish. Risk factors for the development of food allergy include a personal and/or family history of atopy.

The diagnosis of food allergy is based on clinical features, which are classical symptoms of angio-oedema which develop within seconds or minutes to 1–2 hours after ingestion of a specific trigger food, and typically resolve before 12 hours.

In order to make a diagnosis of food allergy clinicians should arrange for skin prick testing and/or serum-specific IgE allergy testing to the suspected food allergens. Allergy testing involve initial skin prick testing or measuring serum-specific IgE levels to different food allergens.

If the results of allergy testing do not correspond with the clinical history, an oral food challenge may be needed to confirm the diagnosis.

Oral food challenge is the gold standard for diagnosis of food allergy. It involves the administration of increasing quantities of the food allergen under medical supervision, starting with direct mucosal exposure (allergen contact with the lips) and then titrated oral ingestion as tolerated. If symptoms are not provoked, the test is negative and clinical allergy can be excluded.

Sadly, when a food allergy has been excluded we know that many people seek solace in a diagnostic approach, which is not evidence based. Some reports have advised that 1 in 5 patients have undergone unproven testing such as serum-specific IgG testing, Vega testing (using electroacupuncture devices), applied kinesiology or hair analysis (allegedly assessing mineral content).

Food allergies have a clear immune mediated pathophysiology which can be proven by testing, food intolerances, although clearly problematic for patients remains a diagnosis of exclusion.

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Gerry Morrow
