Cancer chemoprevention by dietary phytochemicals: Epidemiological evidence.

BACKGROUND: In recent years, natural compounds called "phytochemicals", which are present in fruits, vegetables, and plants, have received special attention due to their potential to interfere with tumour formation and development. Many of these phytochemicals are being used in chemoprevention strategies. However, the scientific evidence regarding the modification of cancer risk continues to be debated.
OBJECTIVE: The aim of this paper is to review the current scientific evidence and the most relevant epidemiological studies regarding the consumption or use of phytochemicals and their effects on the incidence of cancer.
DESIGN: A search for relevant articles was conducted in EMBASE and PubMed-NCBI through to May 2016 to identify potential interactions between the consumption or use of phytochemicals and cancer risk.
RESULTS: The use or consumption of carotenoids, such as lycopene, alpha-carotene, and betacarotene, leads to a reduction in the risk of cancer, such as breast and prostate tumours. For breast cancer, beta-carotene even reduces the risk of recurrence. The use or consumption of soybean isoflavones has led to a reduction in the risk of lung, prostate, colon (in women only), and breast cancers, although this has depended on menopausal and oestrogen receptor status. The use or consumption of isothiocyanates and indole-3-carbinol also seems to reduce the risk of cancer, such as breast, stomach, colorectal, or prostate tumours.
CONCLUSIONS: The adoption of a diet rich in phytochemicals is associated with a modification of cancer risk. However, the scientific data supporting its use come mainly from in vitro and in vivo studies (especially in animal models). The epidemiological evidence is inconclusive for many of these phytochemicals, so further studies are needed.