Strong evidence exists for a preventative effect of reduced fat intake, selenium and soy proteins. A lesser benefit is also suggested with intake of Vitamin D, C and E.

Population studies comparing the eating habits of populations indicate that a fatty diet, particularly one featuring a lot of red meat favours the growth of prostate tumours. The nations, which ingest the most fat, also have the highest prostate cancer death rates. Men in the Pacific Rim nations who consume the least fat have much lower death rates from prostate cancer. Experimental evidence has shown that prostate cancer tumours in mice grew fastest in the group having diets highest in fats.

Soy protein is another dietary component that seems to influence prostate cancer and is consumed in abundance in Japan. These contain a lot of phytoestrogens, which are naturally occurring products, which demonstrate estrogenic effects. Other rich sources of phytoestrogen include the cruciferous vegetables, wholegrain food and red clover. Red clover products on the market include "promensal" for women and "trinivan" for men. The national cancer institute recently suggested that soy food consumption might contribute to the relatively low rates of breast cancer and prostate cancer in countries such as China and Japan. The cruciferous vegetables with high contents of phytoestrogens include broccoli, cabbage, sprouts and cauliflowers.

Vitamins such as Vitamin A, C, E and D and beta-carotene are believed to also have a role in the prevention of prostate cancer. There is however evidence that excessive vitamin use can be dangerous so the correct amount of each one of these is important.

Selenium also has evidence of a protective effect against prostate cancer.

Many other substances have been shown to have some evidence of a protective effect. These include lycopene (tomato based products), DFMO, zinc, co-enzyme Q10 and melatonin.

Some products such as cadmium and pesticides have been shown to increase the risk of prostate cancer.

Finasteride is a tablet, which has recently been tested to see if it protects against the development of prostate cancer. Finasteride inhibits the effect of testosterone in the body. Although it decreases the development of low risk cancers, it does not decrease the risk of more aggressive cancers.