Prostate cancer has become a major public health burden worldwide with an estimated number of 679,000 new cases in the year 2002. This represents 11.7% of all new cancer cases in men (19.03% in developed countries and 5.3% in developing countries) (Ferlay et al. 2004). Diet has been implicated in prostate cancer risk. Studies suggest that men can reduce their risk of prostate cancer by a healthy diet. People in countries such as China and Japan are far less likely than Westerners to develop prostate cancer. Notably, when people migrate to the US, their rates of prostate cancer rise greatly and, since their genetic make- up is the same, there appears to be something about living in America that increases these men’s chances of developing prostate cancer. Diet is the number one suspect.
An interesting observation is that although the incidence of latent (occult, histologically evident) prostate cancer is similar throughout the world, clinical prostate cancer varies from country to country by as much as 20-fold (Wynder et al. 1971). Previous ecologic studies have demonstrated a direct relationship between a country’s prostate cancer-specific mortality rate and average total calories from fat consumed by the country’s population (Armstrong and Doll 1975, Rose and Connolly 1992). Studies of immigrants from Japan have demonstrated that native Japanese have the lowest risk of clinical prostate cancer, first generation Japanese-Americans have an intermediate risk, and subsequent generations have a risk comparable to the U.S. population (Haenszel and Kurihara 1968, Shimizu et al. 1991). Animal models of explanted human prostate cancer have demonstrated decreased tumor growth rates in animals fed a low-fat diet (Wang et al. 1995, Connolly et al. 1997).
Increased dietary intake of fruits and vegetables has been associated with a reduced risk of prostate cancer in some studies. Intake of legumes, yellow orange, and cruciferous vegetables were associated with a lower risk of prostate cancer (Kolonel et al. 2000). A significant difference between Asian and Western diets is the average amount of soy protein consumption (Yip et al. 1999). There is current interest in the possibility that the low risk of prostate cancer in certain Asian populations may result from their high intake of soy products (Miller et al. 1993). Soya beans are widely known for their possible anti-cancer potential, and the latest discoveries are encouraging. It has been found that the beans, which contain compounds called isoflavanoids, can actually inhibit prostate cancer cell growth in the laboratory. Soya protein can be found in many foods such as tofu, soya milk and yoghurt. The Eastern diet is based around soya proteins as an alternative to meat. In one study, Japanese men in Hawaii who consumed tofu approximately once per day, were 65 per cent less likely to develop prostate cancer in comparison with men eating tofu less than once in a week (Severson et al. 1989). In another study, Seventh-day Adventist men in California who consumed soy milk more than once daily were 70% less likely to develop prostate cancer as men who did not consume soy milk (Jacobsen et al. 1998). The pronounced protective effects of soy consumption in these studies are striking. Further work needs to be done to understand its effects on prostate cancer growth and role as dietary inhibitor of prostate cancer development and growth.
Micronutrients in the diet have also been implicated in the pathogenesis of prostate cancer (Platz et al. 1999, Nomura et al. 1997, Hsing et al. 1990a). Many studies showed that men with the highest level of selenium had one third the risk of developing prostate cancer compared with men with the lowest selenium levels (Heinonen et al. 1998, Clark et al. 1997). One of the richest sources of selenium is brazil nuts. Selenium is also found in sunflower seeds, whole wheat bread, avocados and lentils and has been shown to reduce the incidence of prostate cancer. The association between prostate cancer and baseline vitamin E and selenium was evaluated in the trial-based cohort of the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study (ATBC). There were no significant associations between baseline serum alpha-tocopherol, dietary vitamin E, or selenium and prostate cancer overall. The associations between prostate cancer and vitamin E and some of the baseline dietary tocopherols differed significantly by alpha-tocopherol intervention status, with the suggestion of a protective effect for total vitamin E among those who received the alpha-tocopherol intervention (Hartman et al. 1998).
A variety of carotenoids, including lycopene, inhibit prostate cancer cells in vitro (Yip et al. 1999). A higher intake of lycopenes, the agent in tomatoes and beets that gives them their red color, has been shown to decrease risk of prostate cancer (Gann et al. 1999). In a large study of food intake and risk of prostate cancer, Giovannucci and colleagues (1995) demonstrated an inverse relationship between consumption of lycopenes and the risk of prostate cancer. The major dietary sources of lycopenes are cooked tomatoes, tomato juice, and paste. The role of vitamin A in prostate cancer growth is less established (Reichman et al. 1990). Several randomized trials are ongoing evaluating the role of nutrition in preventing prostate cancer progression, but these results will not be available for several years.
A variety of fruits and vegetables are consumed by Indians at varying levels. It is difficult to get the information of specific fruits and vegetables items consumed by the study subjects in India. So we have combined fruits and vegetables and measurements were made on an average basis as how many kilograms of fruits and vegetables were consumed by the subjects in a week. The measurements for oil/fat consumption by the study subjects were also made in a similar way. The aim of the present study was to examine whether a low fat diet rich in fruits and vegetables can reduce the risk of prostate cancer.
