Epidemiological studies have shown marked variations in prostate cancer incidence and mortality across different geographic regions, leading to the rising interest in the role of nutrition in prostate cancer risk.

There is sufficient evidence that a diverse diet, rich in vegetables, can reduce the risk of prostate cancer.

Researchers have now provided a review on prostate cancer and vegetable consumption. Of the available studies for this review, 29 were cohort studies, 69 case-control studies, and 4 randomized clinical trials.

Lycopene
There is accumulating evidence to support the consumption of lycopene, in particular tomato and tomato-based products, as protective factors against prostate cancer. Tomatoes and their byproducts contain the carotenoid antioxidant lycopene. Two cohort studies reported tomatoes decreased prostate cancer risk and 3 cohort studies reported a non-significant association. For case-control studies, 2 showed significant decreased risk and 5 showed a non-significant association. One study suggested that the potential benefit was greater in advanced as compared to localized prostate cancer. Overall, studies for tomatoes and lycopene show inconsistent results on decreasing prostate cancer risk, but lycopene based foods are probably protective.

β-carotene
Yellow orange vegetables contain the antioxidant β-carotene. Data on the protective role of β-carotene and prostate cancer risk from cohort and case-control studies were inconclusive. Supplemental use of β-carotene was not shown to be protective.

Soy
Evidence on the effect of pulses or soy consumption on prostate cancer risk was limited but overall suggestive of decreased prostate cancer risk with increased pulses or soy consumption.

Vitamin C
Vitamin C has had limited study, but with the data available there is no evidence of a protective effect.

Vitamin E
Vitamin E is a naturally occurring fat-soluble vitamin found predominantly in plant foods and some animal foods. In a supplementation trial, there was suggestion that vitamin E was of benefit, but all the participants were smokers. Two other publications failed to show a benefit, and a preliminary report from the selenium and vitamin E trial does not suggest a benefit.

Garlic
As for allium vegetables which include garlic, onions, leeks, chives, scallions and shallots, while in vitro data suggest a protective benefit, population based studies are limited and a protective effect remains to be determined.

Broccoli
Cruciferous vegetables include broccoli, cauliflower Brussels sprouts, cabbage, bok choy, collard greens and kale. These are rich in sulforaphane and indole-3 carbinol, which have anticarcinogenic properties. To date, population-based studies are limited and a positive protective benefit remains to be determined.

Although the impact on prostate cancer risk differs among various vegetables and their constituent nutrients, the existing evidence of the overall benefits of plant-based diet on cancer prevention is significant and should be promoted.
References:
1. Ruth Chan, et al. Prostate cancer and vegetable consumption. Mol Nutr Food Res. 2008 Dec 8;53(2):201-216.
2. UroToday.