The following dietary changes have been studied in connection with prostate cancer.

Avoidance of alcohol
Although the effect of drinking alcohol on prostate cancer risk appears weak, some association between beer drinking and an increased risk may exist, according to an analysis of most published reports.

Tomatoes
Tomatoes contain lycopene—an antioxidant similar in structure to beta-carotene. Most lycopene in our diet comes from tomatoes, though traces of lycopene exist in other foods. Lycopene has been reported to inhibit the proliferation of cancer cells in test tube research.

A review of published research found that higher intake of tomatoes or higher blood levels of lycopene correlated with a reduced risk of cancer in 57 of 72 studies. Findings in 35 of these studies were statistically significant. Evidence of a protective effect for tomato consumption was stronger for prostate cancer than for most other cancers.

Cruciferous vegetables
Cabbage, Brussels sprouts, broccoli, and cauliflower belong to the Brassica family of vegetables, also known as “cruciferous” vegetables. In test tube and animal studies, these foods have shown to have anticancer activity, possibly due to several substances found in them, such as indole-3-carbinol, glucaric acid (calcium D-glucarate), and sulforaphane. A recent preliminary study of men newly diagnosed with prostate cancer showed a 41% decreased risk of prostate cancer among men eating three or more servings of cruciferous vegetables per week, compared with those eating less than one serving per week. Protective effects of cruciferous vegetables were thought to be due to their high concentration of the carotenoids lutein and zeaxanthin, as well as their stimulatory effects on the breakdown of environmental carcinogens associated with prostate cancer.

Meat and how it is cooked
Meat contains high amounts of arachidonic acid. Some by-products of arachidonic acid have promoted prostate cancer in animals. Preliminary reports have suggested that frequently eating well-done steak or cured meats may also increase the risk of prostate cancer in men, though the association between prostate cancer and other meats has not been consistently reported.

Fish
Fish eaters have been reported to have low risk for prostate cancer. The omega-3 fatty acids found in fish are thought by some researchers to be the components of fish responsible for protection against cancer.

Low-fat diet and prevention
When combined with a low-fiber diet, men consuming a high-fat diet have been reported to have higher levels of testosterone, which might increase their risk of prostate cancer. The risk of prostate cancer correlates with dietary fat from country to country, a finding supported in some, but not all, preliminary trials. In one study, prostate cancer patients consuming the most saturated fat (from meat and dairy), and followed for over five years, had over three times the risk of dying from prostate cancer compared with men consuming the least amount of saturated fat.

Avoidance of alpha-linolenic acid
Alpha-linolenic acid is a fatty acid found in many foods. Most, but not all studies have found that high dietary or blood levels of alpha-linolenic acid correlate with an increased risk of prostate cancer.

Concentrations of alpha-linolenic acid are much higher in flaxseed oil, canola oil, soybean oil, and certain nuts compared to the concentrations found in meat. However, because so much meat is consumed as part of many western diets, a significant portion of dietary alpha-linolenic acid often does come from meat. Therefore, at least in theory, alpha-linolenic may merely be a marker for meat consumption. When researchers have adjusted for the intake of meat or saturated fat, however, a correlation between alpha-linolenic acid and prostate cancer risk has remained. On the other hand, in a preliminary study of men with prostate cancer, supplementation with 30 grams of ground flaxseed per day for approximately one month appeared to decrease the rate of tumor growth.

How alpha-linolenic acid might increase the risk of prostate cancer remains unclear. Alpha-linolenic acid has promoted the growth of prostate cancer cells in one test tube study, but inhibited prostate cell growth in another.

Soy
Genistein is an isoflavone found in soybeans and many soy foods, such as tofu, soy milk, and some soy protein powders. Except for soy sauce and soy protein concentrates processed with alcohol, most soy-based foods contain significant amounts of isoflavones, such as genistein. Genistein inhibits growth of prostate cancer cells, helps kill these cells, and has other known anticancer actions, according to test tube research findings.

In preliminary research, men who consumed soy milk more than once per day were reported to have a significantly lower risk of prostate cancer compared with other men. Some researchers are now saying that genistein may eventually be shown to have the potential to treat prostate cancer, while others say only that enough evidence exists to recommend that future genistein research be devoted to the subject of prostate cancer prevention.