I looked it up on the internet and found this.

Early research by Max Gerson, M.D. founder of the Gerson Institute and Gerson Diet Therapy, recognized that the coffee enema is effective in stimulating a complex enzyme system involved in liver detoxification (called the gluthathione-S-transferase enzyme system). The increased activity of these enzymes ensures that free-radical activity is greatly diminished and that the activity of carcinogens is blocked.

"The coffee enema is capable of purging toxins and partial metabolites (products formed and released during metabolism, or the extraction of energy from foods) because the enema dilates the bile ducts and stimulates an enzyme system that is capable of removing numerous toxins from the blood," says Dr. Etienne Callebout. "The activity of the glutathione enzyme system is increased by at least 600% above normal." Caffeine also stimulates dilation of blood vessels and relaxation of smooth muscles, which further increases bile flow; this effect does not happen when the coffee is consumed orally.

-from An Alternative Medicine Definitive Guide to Cancer by W. John Diamond, M.D. and W. Lee Cowden, M.D. with Burton Goldberg