arcinogenesis is an incredibly complex process and the exact aetiology is not fully understood. Mainstream medicine has failed to make any progress at reducing cancer rates because the paradigm adopted by the pharmaceutical companies is one that seeks maximum profit from treating cancer, while having little interest in its prevention. However, the nutritional sciences have made great advances in understanding the anti-cancer activity of plant compounds, and in this regard lead the way from mainstream medicine. A large number of different plant compounds are able to inhibit the development of cancer in various ways, and this process may begin nutritionally before the carcinogen even enters the body. In the gut, dietary fibre can inhibit the uptake of many carcinogenic substances by irreversible binding and increased excretion rates. This may explain the epidemiological findings that consistently show fibre to lower the risk of bowel cancer.
Detoxification is a highly important process in the inhibition of carcinogenesis, and probably the step most influenced by phytonutrients. A large number of plant compounds are able to modify detoxification enzymes and prevent the formation of carcinogenic substances. Detoxification of any absorbed pro-carcinogens occurs through a two step process, whereby the compounds are activated via phase I detoxification enzymes and then made more water soluble for excretion via phase II detoxification enzymes. The activated intermediates of certain compounds can initiate cancer. Compounds that inhibit phase I detoxification and induce phase II detoxification, such as carotenoids (fruits and vegetables), chlorophyllin (leafy vegetables), courmarins (vegetables, citrus fruit), diallyl sulphides (onion, garlic), flavonoids (fruits and vegetables), indoles (cruciferous vegetables), organic isothiocyanates (cruciferous vegetables), phenolic acids (tea, coffee, fruits and vegetables) and plant sterols (fruits and vegetables) can reduce the production of these activated intermediates.
Once formed, such phase I activated intermediated tend to be chemically reactive. In particular, they show reactivity through the generation of free radical chain reactions, which can damage cell components. Antioxidants such as flavonoids and phenolic acids can inhibit the DNA, RNA and protein damage by activated intermediates because they are in vivo reducing agents. This antioxidant effect of flavonoids and phenolic acids is believed to be their primary mechanism of action in preventing cancer in humans. That free radical production may initiate cancer has been theorised since Denham Harman postulated the free radical theory of disease in the 1950’s. In addition, flavonoids, chlorophyllin, indoles, organic isothiocyanates and phenolic acids may prevent the reaction of carcinogens with DNA molecules. Phenolic compounds may also shield the nucleophilic (electron donor) sites in DNA from the activated phase I intermediates, which tend to be electrophilic (electron accepting; oxidising) in nature.
Epidemiological studies show anti-cancer effects for a number of plant compounds. In particular, tea consumption shows consistent benefits with regard a reduction in the risk of cancer. Tea might be important nutritionally with respect to cancer because it is consumed by such a large number of people in large amounts. Both black tea and green tea appear effective at preventing cancer, but green tea shows more consistent protective effects. That many plant compounds have different mechanisms of action against cancer suggests that synergism may increase the effect of a diet rich in plant foods. The inconsistent results of clinical trials attests to this theory and demonstrates the methodological flaws inherent in testing nutrients like pharmaceuticals. The benefits of plant compounds in preventing cancer are likely subtle and take decades to manifest, and further support the evidence that high quality diets containing large quantities of fruits and vegetables are beneficial to long-term health.
RdB
