Decreased growth of human prostate LNCaP tumors in SCID mice fed a low-fat, soy protein diet with isoflavones

Epidemiological studies suggest that high intake of dietary fat is a risk f actor for the development of clinical prostate cancer. Soy protein has also been proposed to play a role in the prevention of prostate cancer, and one of the isoflavones in soy protein, genistein, inhibits the growth of human prostate cancer cell lines in vitro. This study was designed to evaluate w hether altering dietary fat, soy protein, and isoflavone content affects th e growth rate of a human androgen-sensitive prostate cancer cell line (LNCa P) grown in severe-combined immunodeficient (SCID) mice. SCID mice were ran domized into four dietary groups. high-fat (42.0 kcal%) + casein, high-fat (42.0 kcal%) + soy protein + isoflavone extract, low-fat (12.0 kcal%) + cas ein, and low-fat (12.0 kcal%) + soy protein + isoflavone extract. After two weeks on these diets, the mice were injected subcutaneously with 1 x 10(5) LNCaP tumor cells and placed in separate cages (I mouse/cage) to strictly control caloric intake. Isocaloric diets were given 3 days/wk, and tumor si zes were measured once per week. The tumor growth rates were slightly reduc ed in the group that received the low-fat + soy protein + isoflavone extrac t diet compared with the other groups combined (p < 0.05). In addition, the final tumor weights were reduced by 15% in the group that received the low -fat + soy protein + isoflavone extract diet compared with the other groups combined (p < 0.05). In this xenograft model for prostate cancer, there we re statistically significant effects on tumor growth rate and final tumor w eight attributable to a low-fat + soy protein + isoflavone extract diet.