| ABSTRACT: |
|
Considerable circumstantial evidence exists that implies a
relationship between dietary intake and the incidence of cancer. This
evidence derives from (1) epidemiologic data accumulated from humans and
(2) experimental results obtained in animal model systems. Data
associating vegetable and fruit consumption with the inhibition of cancer
are reviewed, including diet and cancer incidence, experimental
carcinogenesis, mutagenesis, carcinogens/drug metabolism, and studies on
particular compounds found in fruits and vegetables (indoles, thiocyanates
and isothiocyanates, flavonoids, ellagic acid and other phenols, terpenes,
sulfides, and protease inhibitors). Epidemiologic studies have provided
circumstantial evidence for cancer prevention by dietary vegetables and
fruits. Gastrointestinal tract cancers and other cancers (lung, bladder,
breast and prostate) have been involved in these associations. Few studies
have been conducted on the inhibition of cancer in animals fed vegetables.
Such studies have yielded inconsistent results; vegetable supplements can
inhibit, enhance, or not influence carcinogenesis. Numerous factors could
influence these results. Several studies have demonstrated potential
antimutagenic properties of vegetable and fruit extracts. Several of the
indoles were shown to influence metabolism of drugs and carcinogens.
Indole-3-carbinol inhibits initiation of several forms of cancer, but it
also appears to enhance the promotion of cancer in some model systems.
Isothiocyanates have been studied as initiation inhibitors. More work
needs to be done on the flavonoids, which are a diverse group of compounds
that are ubiquitous in plants. Ellagic acid, D-limonene and allyl sulfides
have been shown to inhibit initiation. Protease inhibitors appear to
interfere with the promotion of skin cancer and the expression and
promotion stages of radiation-induced transformations. Inhibition of
free-radical generation may account for some of these effects. The
potential for finding new chemopreventive agents in plants is high. (201
Refs) |