Title: Non-immunological forms of food intolerance
Key words: lactose, intolerance, food allergy, lactase, fermentation, gut bacteria, enzyme, flatus, diarrhoea, intestinal motility, disaccharide, fructose, milk protein, hydrogen breath test, histamine, biogenic amine, asthma, urticaria, angioneurotic oedema, mast cells, benzoates, fish, aubergines, spinach, tomatoes, strawberries, inflammatory, redness, swelling, itching, rhinitis, conjunctivitis, bronchospasm, tachycardia, flushing, food challenge, monosodium glutamate, MSG, Chinese Restaurant syndrome, glutamates, dopamine, acetyl choline, neurotransmitters, sensitivity
Date: Sept 2006
Category: The Gut
Author: Morgan, G
Non-immunological forms of food intolerance
Food allergy and intolerances involving immunological pathways have been widely reported in the literature. Here three causes of non-immunologically mediated food intolerances are described.
This is a relatively common cause of gastrointestinal disturbance affecting up to nearly 100% of certain populations such as the Chinese. It is caused by functional underactivity of the enzyme lactase. It is rarely congenital, most cases being acquired after weaning. Deficiency of the enzyme leads to the inability to break down the sugar lactose, present in large amounts in milk, into glucose and galactose. Accumulation of undigested lactose in the gut leads to its fermentation by bacteria leading to the production of hydrogen gas, fatty acids and fermentation products. Gas production, lowered pH and increased osmotic pressure lead to the flatus, increased intestinal motility and diarrhoea associated with the condition.
Identification of lactose intolerance requires withdrawal of lactose containing foods from the diet and a subsequent challenge test. Individuals differ in the quantity of milk they are able to tolerate. It needs to be distinguished from other disaccharide intolerances such as fructose intolerance : reintroducing fruit into a sugar free diet would precipitate a relapse in this instance. Distinguishing milk protein from lactose intolerance is best achieved through carrying out a lactose tolerance of a hydrogen breath test.
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Histamine is a biogenic amine involved in IgE mediated Type I inflammatory reactions, including some cases of food mediated allergic reactions associated with asthma, angioneurotic oedema, urticaria and other acute skin conditions. Release of the bioactive amine by mast cells may also be precipitated by certain food chemicals such as benzoates via non- immunological pathways. In subjects who are especially sensitive, ingestion of foods particularly rich in histamine, such as spoiled fish, cheeses, aubergines, spinach, tomatoes, strawberries and preserved foods, may lead to the direct pharmacological effects of histamine being displayed.
Such effects include smooth muscle contraction, increased capillary permeability and local inflammatory changes such as redness, swelling, and itching. Local and general symptoms may include rhinitis, conjunctivitis, bronchospasm, low blood pressure, tachycardia, flushing and urticaria.
Histamine sensitivity has also been linked with some more chronic conditions, for example chronic urticaria and some types of headache. Antihistamines may be of some help in these conditions. Confirmation of histamine sensitivity requires removal of all sensitising foodstuffs. After stabilisation on a histamine free diet, food challenges with high histamine containing foods, such as aubergines and spinach, will help to confirm the diagnosis.
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Monosodium glutamate sensitivity
Monosodium glutamate (MSG) ingestion has been linked to the so-called ‘Chinese Restaurant Syndrome’, a syndrome characterised by pain, numbness and paraesthesiae in the head, neck and chest coming on within an hour of consuming MSG. It is usually accompanied with an array of acute symptoms including headache, facial flushing, blurred vision, palpitations, nausea and vomiting. Double-blind studies have produced results that are difficult to reproduce in the laboratory indicating that it is perhaps the combination of MSG, salt and other factors that are necessary to reproduce the full ‘Chinese Restaurant Syndrome’ picture.
Although glutamates are naturally occurring in foods, artificial MSG is rapidly absorbed in the stomach and may lead to blood levels some 15 times higher than baseline values. Experiments in animals have shown that even at these levels glutamates pose no pharmacological threat in man. Levels of 2.5G, reported to precipitate symptoms in sensitive individuals, are far below toxicological doses. Nevertheless it has been shown in mice that high glutamate levels impact upon the neurotransmitters dopamine and acetyl choline in the hypothalamic region leading to changes on a neurological and endocrine level. As glutamates are intimately involved in neurotransmitter chemistry this may well be the pathway of their action in sensitive individuals.
MSG is widely used in Chinese and Japanese cookery and the context of any reaction usually makes it clear that the source was MSG rather than any specific food item. Avoidance of high MSG containing foods in Chinese restaurants is all that is required, though a few sufferers have reported to be sensitive to the much smaller amounts present in some canned and preserved foods.
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