Hi Kelly,
You said:
<<Grapefruit contains a substance (naringin I believe) that prolongs and
intensifies the action of some other drugs. >>
Grapefruit potentiates drugs metabolized by the CYP450 2D6 isozyme
by inducing the 2D6 isozyme, causing a more rapid assimilation of
these drugs. Most commonly, these are the class of drugs called
SSRI antidepressants.
The P450 enzyme system is also responsible for metabolizing many
foods. If a person is genetically inclined to have less of a particular
P450 enzyme, then foods that are metabolized by the partcular enzyme
would not serve this person well.
This barely and inadequately touches on the topc of the P450 enzymes
Regards,
Catherine