FALSE FOOD ALLERGY: WHEN FOOD BITES BACK (LECTINS)
The main characteristic of lectins is that they bind to carbohydrate molecules carried on the surface of all cells. As a result, they make red blood cells clump together, and this is how they are recognized in the laboratory. The deadly poison, ricin, used in the KGB’s infamous umbrella-tip murder of George Markov, is a type of lectin. Fortunately not all lectins are as potent as this, but many can cause rather more subtle damage. Apart from triggering mast cells, they can also bind to the lining of the gut wall and make it more leaky, so that more undigested food molecules get into the blood stream. These molecules can act as allergens, causing further damage as they travel around the body in the blood. There is also some evidence that, in atopic individuals, certain lectins can stimulate the body to produce IgE in preference to other antibodies. All these different effects could contribute to adverse reactions to food, but the major factor in false food allergy is the direct effect of lectins on mast cells.
Many lectins are inactivated by cooking, but they need to be heated for a long time and at fairly high temperatures to destroy all their activity. The powerful lectin found in kidney beans or haricot beans (Phaseolus vulgaris) can cause serious diarrhoea and abdominal pain if the beans are not soaked and cooked properly. Using low-temperature ‘slow-cookers’ to prepare casseroles containing beans has caused many outbreaks of such illness.
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