The objective 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 determine if high levels of phytosterols could inhibit these enzymes, the researchers fed one group of rats a standard, or basal, diet. A second group, designated the control group, ate the standard diet plus cholic acid, which stimulates the absorption of vegetable fats. A third group ate a 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, results showed. 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."