ABSTRACT
As every clinician knows, the small intestine is not just a passive membrane. A major part of its complex function is the active absorption of nutrients, salts and some vitamins. What many people still don’t know is that the small intestine also has a powerful drug-metabolising mechanism whose evolutionary function was to detoxify poisonous materials ingested with food, preventing their absorption and rendering them harmless. This mechanism includes enzymes identical to the drug-metabolising liver enzymes – the so-called cytochrome P450 oxidase system Note that it doesn't matter at what time the grapefruit juice is consumed the intestinal metabolic enzymes will be 'knocked out' for 24 hours. Some authorities, who should know better, suggest that a litre of grapefruit juice must be consumed to cause this effect. This is not so a 250-ml glass is enough to affect the intestinal enzymes as described.
