These reactions have been referred to as food intolerances and involve non immunological mechanisms. Like true food allergies, food intolerances affect some people only, and usually they can tolerate small amounts of the offending food without adverse effects. Metabolic food disorders can be either due to inherited defects in the metabolism of a food or food component or due to genetically linked enhanced sensitivity to some food chemical. For example, individuals with lactose intolerance lack the enzyme lactase or b-galactosidase in the intestinal mucosa. As a result, such individuals cannot hydrolyze lactose or milk sugar into its monosaccharide’s, galactose and glucose. The undigested lactose cannot be absorbed, so it passes down the small intestine to the colon, where bacteria ferment it. Fermentation of lactose to carbon dioxide, water, and acetic acid results in gas, abdominal cramping, and diarrhea. Other examples include individuals with sucrose deficiency, fructose intolerance, galactosemia, and phenylketonuria. Individuals taking drugs that inhibit monoamine oxidase enzymes can be affected when eating cheeses or drinking wines, which are high in tyramine. Individuals sensitive to cabbage exhibit goiter, because isothiocyanates present in cabbage interfere with the utilization of iodine.
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