Legumes play an important role in traditional diets in many parts of the world. They are low in fat, are good sources of protein and fiber, and contain a variety of micronutrients and phytoestrogens (plant estrogens). Phytoestrogens have received a lot of attention for their ability to fight not only cancer, but also heart disease and osteoporosis. They help balance hormones in the body and thus are thought to be particularly valuable for the hormone-dependent cancers: breast cancer and prostate cancer. It is well known that male hormones play a role in prostate cancer development.

Despite their advantages, legumes play a minor role in most Western diets. The typical Western based diet (lower in vegetables and legumes and higher in animal-based foods) can cause an increase in both male and female hormones (androgens and estrogens), while a plant-based diet tends to lower these hormones. This is the basis for the role of diet in the development of hormone-dependent cancers.

Soy foods, such as tofu, soy milk, soy beans, and vegetarian burgers, seem to be particularly rich in cancer-fighting properties. This is at least partially due to a form of phytoestrogen, called isoflavones, that is found primarily in soy. It appears to help prevent prostate cancer by binding to male hormone receptors in the prostate, thus reducing the stimulating effect of male hormones on prostate cell growth.

Epidemiological studies have shown that high levels of isoflavones are often associated with low rates of breast, colon, and prostate cancer. This has been used to explain why countries such as Japan and China that typically consume large amounts of soy have lower risks of these diseases.

The difficulty with consuming soy for reducing risk of prostate cancer is the lack of clinical trial evidence to support its use. As with any dietary component, it is difficult to isolate the effect of a particular food type to prove its effectiveness. One prospective study, including over 12,000 men, did evaluate consumption of soy milk. It found that those who drank soy milk regularly had a reduced risk of prostate cancer. The relationship held up after other factors were controlled for. Other studies need to be done to further establish the benefits of soy. In the meantime, getting more soy foods into your diet can be healthy for many reasons, and lowering your risk of prostate cancer may be one of these.