The most common presentation of reactions to foods due to enzyme deficiencies, is lactose intolerance. This involves abdominal pain, bloating, diarrhoea, flatulence and occasionally nausea and vomiting after ingesting milk, due to a deficiency of the enzyme lactase. Lactose intolerance is most prevalent in people of Indian, South American or African heritage. A history of gastro-intestinal symptoms linked to milk is a useful guide and a 4-week exclusion of milk and milk products followed by symptom improvement may be diagnostic. A diagnosis can also be reached by performing a hydrogen breath test, which has good sensitivity and specificity. A test is considered to be positive if the breath hydrogen level is ≥ 20 ppm above baseline and/or methane is ≥ 15 ppm. Intolerance to fructose, the sugar in fruit, honey and some syrups, should be considered if symptoms persist despite exclusion of lactose, or if a lactose breath test is negative.
Bacterial degradation of food during fermentation, storage or decay leads to the presence of vasoactive amines. The most well-known of these is the diamine, histamine, but other amines such as tyramine, a monoamine, can also be relevant. Most people will react to a very high level of histamine in foods, but some may also be sensitive to much smaller amounts. There are no recommended tests to diagnose histamine sensitivity, although the Diamine Oxidase test is sometimes advocated it is not currently a test recommended in guidelines. A better test is a 4-week exclusion of high histamine foods, followed by sequential re-introduction.
Aspirin is a synthetic derivative of salicylic acid, which is widely distributed in plant foods. It has been proposed that salicylic acid or salicylates could provoke pharmacological adverse reactions in those with aspirin-exacerbated respiratory disease, or functional gut disease. The published data on the salicylic acid content of foods is highly variable and there are currently no controlled studies demonstrating the efficacy of a low salicylate diet. Pharmacological reactions can also occur to caffeine and theobromine, naturally occurring substances in coffee tea and chocolate.
Food additives can cause IgE-mediated reactions if they are derived from natural sources. These include the red colouring cochineal (carmine), derived from insects, and yellow colouring annatto derived from the shrub Bixa Orellana. Synthetic colourings have also been linked to adverse reactions, but there is little recent evidence and the mechanisms are largely unknown. Sulphites, which are preservatives and also used to prevent browning, are well documented to provoke reactions, especially in people with asthma. Sulphites are often found in white and rose wine, cider, lager, dried fruits, fruit juices/cordial, frozen cooked prawns, frozen raw potato products, and some meat products. Another food preservative which might provoke oral symptoms is benzoate, which also occurs naturally in cinnamon, cloves, tea, plums, raspberries and cranberries. The exclusion of these foods, and foods with added benzoate can improve symptoms in patients suffering from orofacial granulomatosis. Monosodium glutamate (MSG) is another food additive which has been linked to allergic reactions, although research evidence is weak. As well as being an added ingredient, glutamates are also found naturally in mushrooms and spinach.
Other types of food intolerance usually linked to reactions in adult life are most frequently due to functional gut disorders or spontaneous urticaria/angio-oedema. There is very little evidence that spontaneous or chronic urticaria responds to dietary manipulation, although some do gain symptomatic relief from the exclusion of high histamine foods. Functional gut disorders often involve reactions to lactose, fructose or histamine, although many respond to the exclusion of Fermentable, Oligo-, Di-, Mono-saccharides and Polyols (FODMAPS™).