Diets rich in tomato sauces appear to reduce the risk of prostate cancer, according to a Harvard Medical School study. The most likely reason appears to be tomatoes' high content of lycopene, a red carotenoid related to beta-carotene.
In an ongoing study, Edward Giovannucci, MD, examined the dietary habits and health of 47,894 male health care professionals. Between 1986 and 1992, 812 of the men were diagnosed with prostate cancer. When Giovannucci analyzed 46 vegetables and fruits in the men's diets, he found four foods associated with a low risk of developing prostate cancer: tomato sauce (on spaghetti), pizza (with tomato sauce), tomatoes, and strawberries.
The men who ate the most of these foods were least likely to develop prostate cancer. Those who ate few tomato foods had the highest risk, according to Giovannucci's article in the Journal of the National Cancer Institute (Dec 6, 1995;87:1767-76).
Despite their red color, strawberries do not contain lycopene. Their inverse relationship to prostate may have been due to a statistical fluke or to some other nutritional component (such as a flavonoid).
Men who ate 10 or more servings of tomato foods weekly were 45 percent less likely to develop prostate cancer. Those who ate four to seven servings of tomato foods were 20 percent less likely to develop the disease.
Giovannucci's findings are consistent with other studies that have reported a low incidence of prostate cancer in southern Mediterranean countries, including Italy and Greece, where tomato consumption is high. (viva italia!)
Diets with abundant tomatoes cooked in oil - such as spaghetti sauce - were more readily absorbed than other forms of tomato. Pizzas and raw tomatoes were also protective against prostate cancer, but tomato juice was not.
The reason was twofold, according to Giovannucci. First, cooking broke down the tomatoes' cell walls, releasing more lycopene. Second, the oil enhanced absorption of the fat-soluble carotenoid. (It's possible that the oil in salad dressings enhances lycopene absorption with raw tomatoes.)
Other carotenoids, such as beta-carotene, did not affect the risk of prostate cancer, although they may very well influence the risk of other diseases. Dietary intake of vitamins C and E was not a factor in prostate cancer either. Nor was vitamin A-the body does not convert lycopene to vitamin A.
Although tomatoes contain many other micronutrients, further analysis by Giovannucci strengthened the association between lycopene and low prostate cancer risk.
In general, men in this study had two times as much lycopene as beta-carotene in their blood, and lycopene is the most abundant carotenoid stored in the prostate gland. It is also a powerful antioxidant that can quench singlet-oxygen free radicals twice as efficiently as can beta-carotene.
Diets low in tomato provide virtually no lycopene. However, other studies have shown that blood levels of the nutrient increase dramatically within one day of eating a high-lycopene meal. They also decrease after a low-lycopene diet, suggesting that the nutrient is not stored in the body for long periods.
