Plants contain a wide range of biologically active compounds, some of which are known as phytochemicals. There may be as many as 100000 different compounds, which determine particular properties in plants, and in the fruits and vegetables they produce, such as flavor and color. Phytochemicals are classified according to their chemical structure and functional characteristics, and include salicylates, phytosterols, saponins, glucosinolates, polyphenols, protease inhibitors, monoterpenes, phytoestrogens, sulphides, terpenes, and lectins.
It is widely believed that the health benefits of diets high in fruits and vegetables are likely to be due partly to the presence of phytochemicals. For instance, several act as antioxidants, preventing oxidative damage to cells, proteins, and DNA. It is likely that other bioactive phytochemicals have yet to be identified, and those that are known may have additional properties in the body that are not yet understood. But it is thought that nutrients, phytochemicals, and other, as yet unknown, bioactive components act together to influence physiological responses.
Although many phytochemicals are bioactive, they are not essential in the diet and there is no daily requirement, so they are not classed as nutrients. Humans have developed tastes for some phytochemicals, such as the hot flavors of mustard oil, bitter alkaloids, and irritating capsaicins. There is genetically inherited variation in sensitivity to some tastes, for example, the bitter taste of isothiocynates in cruciferous vegetables such as cabbage.
Examples of phytochemicals which can prevent cancer:
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From veggie burgers to milk to protein bars, soy beans are known as a nutrient rich ingredient- there are studies showing soy bean can prevent prostate cancers.
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Pomegranate phytochemical urolithin B suppresses estrogen production and that prevents the proliferation of breast cancer cells and the growth of estrogen-responsive tumors- Cancer Prevention Research, Jan 2010.
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Phytochemicals (vitamins A, C, K, folate, carotenoids and lutein) from leafy veggies and green tea showed lower levels of genetic changes known to give rise to lung cancer in smokers-Cancer Research, Jan 2010.
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Apples contain natural phytochemicals that have a protective effect against liver, breast and colon cancer-Journal of Agricultural and Food Chemistry, Apr 2008.
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Mangos are known to be rich in vitamins C and A, as well as fiber. Polyphenolic compounds in mangos known as gallotannins, a class of natural bioactive compounds believed to help prevent or block the growth of cancer cells-Jan 2010. http://agnews.tamu.edu/showstory.php?id=1686
Reference: Reports from American Institute for Cancer Research