I found this very interesting...
Grapefruit juice significantly increases the production and activity of liver detoxification enzymes responsible for preparing toxic compounds for elimination from the body.
The liver clears out toxins, including carcinogens, using a two step process called Phase I and Phase II detoxification. In the first part of this process, Phase I, enzymes belonging to the cytochrome P450 family, work on the toxin to make it more attractive to enzymes involved in the second part of the process, Phase II. Unfortunately, the action of Phase I enzymes often renders the toxin not only more attractive to Phase II enzymes, but even more dangerous, and some foods contain compounds that only increase the activity of Phase I without also turning up Phase II.
Grapefruit increases the activity not only of the Phase I enzyme CYP1A1, but also that of NAD(P)H:quinone reductase 1, a Phase II detoxification enzyme that protects cells against oxidative stress and toxic quinones.
The end result: grapefruit works in both Phase I and Phase II to enhance the liver's ability to remove cancer-causing toxins
And from www.cancer.gov
phase I detoxification
A process in which the liver uses one of two major enzyme pathways to change a toxic substance, such as an anticancer drug, into a less toxic substance that is easier for the body to excrete.
phase II detoxification
A process in which the liver uses one of two major enzyme pathways to change a toxic substance, such as an anticancer drug, into a less toxic substance that is easier for the body to excrete. In phase II detoxification, liver cells add a substance (such as cysteine, glycine, or a sulfur molecule) to a toxic chemical or drug, to make it less harmful.