Nutrients found in vegetables and fruits, have health benefits. The 1995 Dietary Guidelines for Americans, released by the US government, states that "The antioxidant nutrients found in plant foods (vitamin C, carotene, vitamin E, and the mineral selenium) are presently of great interest to scientists and the public because of their potentially beneficial role in reducing the risk of cancer and certain other chronic diseases."
Many claims about plants and health have not been tested in clinical, double-blind trials or by other traditional means. Should we believe them? The universal acceptance of the benefits of plant phytochemicals-substances found in plants that might play a role in preventive health-might at least nudge us toward the willingness to accept the possibility that plants have benefits.
Some of the research on phytochemicals is funded by the National Cancer Institute (NCI), which has launched a multimillion-dollar project to find, isolate, and study phytochemicals. The result of this and similar research is an ever-increasing wealth of data that points to the possible positive effects of fruits and vegetables on our health.
For example, research has shown that broccoli contains a substance, sulforaphane, that may prevent, even cure, breast cancer. Citrus fruits contain limone, which increases the activity of enzymes that eliminate carcinogens. Cabbage, Brussels sprouts, cauliflower, and similar vegetables contain indoles, which might lower the risk of breast cancer. Currently in the news is genistein, a substance found in soy beans which may block tumor growth, and lycopene, a component of tomatoes which has been linked to reduced risk of prostate cancer.
One of the results of this research is that the NCI recommends that we eat five servings of vegetables and three servings of fruits per day.