Anticancer Properties of Fruits and Vegetables

Abstract

Routine or habitual consumption of fruits and vegetables has been strongly associated with reduced risk for many of the common cancers (Steinmetz and Potter, 1991). The strongest evidence pertains to reduced risk for cancers of the mouth and pharynx, esophagus, lung, stomach, and colon. A moderately strong case can also be made for cancers of the breast, pancreas, and bladder. For other cancers, data are not sufficient to draw a conclusion on the effects of fruits and vegetables (American Institute for Cancer Research, 1997). Available scientific evidence suggests that some components of fruits and vegetables inhibit cancer; therefore, experiments have been conducted to pinpoint which foods provide the most benefit. With the increased ability to isolate and structurally identify phytochemicals in fruits and vegetables, cancer researchers have tested everything from fresh or freeze-dried fruits and vegetables to highly purified agents for cancer prevention. Both cell culture and in vivo studies in animal cancer models have solidly seconded data from human population studies. This paper will review some of the epidemiologic evidence for protection against the development of cancer in populations that consume fruits and vegetables. Also, the four basic mechanisms by which elements in foods can reduce the risk for cancer will be explored using data from animal carcinogenesis models. THE EVIDENCE FOR FRUITS AND VEGETABLES AS CANCER PREVENTIVES IN HUMANS Few studies in humans have evaluated the effect of consuming fruits and vegetables on cancer risk, and most of the available data come from case-control studies where eating patterns in people with cancer were compared with those of control subjects without cancer. One of the problems in assessing the effects of fruit and vegetable intake is the wide variety of these foods available. In a recent report of the expert panel assembled by the American Institute for Cancer Research (1997), a protective role for fruit and vegetable intake was ascribed for four tumor sites: oral-pharynx/esophagus, lung, stomach, and colon. The report inferred that available data are also strong supporting reduced risk for pancreas, breast, and bladder cancer in consumers of fruits and vegetables, and concluded that no increase in cancer risk has been reported for habitual consumers of fruits and vegetables at any tumor site. This is taken in context of concerns that minor contaminants such as fertilizers and pesticides may potentially pose a risk. The available evidence supports claims that fresh fruits and vegetables, when properly harvested, processed, and stored, help reduce risk for certain forms of cancer. MECHANISMS BY WHICH FRUITS AND VEGETABLES