Plant-based Fat May
Reduce Risk of Prostate Cancer

February 23, 1999. Plant-based fats may cut the risk of prostate cancer by reducing the levels of testosterone. These fats may also reduce enzymes that metabolize testosterone into more active forms, a new study by University at Buffalo nutrition researchers suggests.
     The study, published in the Journal of Nutritional Biochemistry, reported that feeding rats a diet rich in phytosterols, the type of fat found in plants, reduced testosterone in the blood stream by 33 percent. A high level of testosterone is one possible risk factor for developing prostate cancer.
     A diet high in plants fats also reduced levels of 5-alpha reductase and aromatase. These two enzymes help metabolize testosterone into end products that also are implicated in the development of prostate cancer. In rats on the high plant-fat diet, the enzymes were cut by 44 percent and 55 percent respectively.
     Atif Awad, Ph.D. and colleagues have been trying to understand exactly why vegetarians have lower rates of hormone-dependent cancers, They are also trying to pin down causes of lower mortality rate from prostate cancer in Asian countries, where populations eat little meat.
     With fats known to play a role in the development of several cancers, Awad's group has been focusing on the phytosterols for possible answers. He reported at an international conference on cancer research in Greece last October that the phytosterol B-sitosterol appears to play a role in inhibiting the growth of human prostate-cancer cells by strengthening an intracellular signaling system that inhibits cell division.
     The aim of the current study was to examine the influence of vegetable fats on the metabolism of testosterone in liver, testis and prostate tissue in rats.
     The fact that prostate cancer doesn't develop in men castrated before puberty or in men who have low levels of 5-a reductase suggested to Awad's group that suppressing the action of the enzyme might be useful in preventing prostate cancer in high-risk groups. The enzyme aromatase converts testosterone to estrogen, also considered a possible risk factor for prostate cancer.
     To see if high levels of phytosterols could inhibit these enzymes, the researchers fed one group of rats a standard (or basal) diet. A control group ate the standard diet plus cholic acid, which helps the body absorb vegetable fats. A third group ate the standard diet enhanced with a mixture of phytosterols, plus cholic acid. The trial lasted 22 days.
     Results showed that rats fed the phytosterol diet had between 33 and 48 percent less testosterone than the animals that received no additional phytosterols. There was no difference in serum testosterone levels between the basal and control groups.
     The enhanced diet reduced the activity of 5-a reductase by 44 percent in the liver and by 33 percent in the prostate, but did not affect the enzyme's activity in the testis. Phytosterols reduced the activity of aromatase by 57 percent in the prostate, but had no effect in the liver or testis.
     Awad said his research team continues to examine exactly how phytosterols bring about these changes, but he believes one pathway involves the "fluidity" of membranes that harbor the enzymes. "Every enzyme requires a specific fluidity in the membrane in which it resides in order to be activated," he said. "If the membrane is too fluid, the enzymes may not function properly."
     Other options include the possibility that phytosterols compete with testosterone and its products of metabolism for the enzyme's active receptors, or that they reduce production of the enzymes themselves.
     "At any rate, the combined effect of reducing levels of testosterone and reducing the activity of its two main enzymes suggests that a diet high in foods containing phytosterols could help reduce the risk of prostate cancer," Awad said.

Dr. Atif Awad is an associate professor in the Department of Physical Therapy, Exercise and Nutrition Sciences in the University of Buffalo School of Health Related Professions.He is director of UB's Nutrition Program. Also working on the study were Maria Sri Hartati, a master's degree student, and Carol S. Fink, Ph.D., UB clinical assistant professor of nutrition. The research was supported by a grant from the Allen Foundation

Earlier work this study refers to:
"Plant-Based Fat Inhibits Cancer Cell Growth By Enhancing Cell's Signaling System, UB Researchers Show"

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