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The Effect of Phytosterols on Male Testosterone

Phytosterols, also called plant sterols, are plant-based compounds that compete with dietary cholesterol in your intestines. The intake of phytosterols may reduce the amount of cholesterol absorbed from your intestines and lower blood cholesterol levels. Phytosterols may impact testosterone metabolism in males through their interactions with the 5-alpha-reductase enzyme. Although animal models show that a high intake of phytosterols will reduce serum testosterone levels, human trials thus far have failed to demonstrate such effects.

  1. Phytosterols

    • Phytosterols are found in certain plants and are similar in structure to the cholesterol molecule. Foods that are particularly rich in phytosterols include natural vegetable oils, unprocessed grains, nuts and legumes. Phytosterols reduce the amount of cholesterol we absorb from food, and therefore lower serum LDL cholesterol (i.e. bad cholesterol). The National Cholesterol Education Program recommends 2 g of plant sterols per day for dietary therapy for elevated LDL cholesterol.

      Some studies, such as "Dietary phytosterol inhibits the growth and metastasis of MDA-MB-231 human breast cancer cells grown in SCID mice," which was published in the March-April 2000 edition of the Anticancer Research Journal, have also found high phytosterol diets to lower the incidence of cancer, although the results are not conclusive as of yet.

    Testosterone

    • Testosterone is a hormone that is produced primarily in the male testes and is responsible for many of the male traits, such as facial hair, deep voice and muscle tone. In men as well as women, a limited amount of testosterone is also manufactured in the adrenal gland (which is why females also have testosterone, despite lacking testes). Numerous enzymes interact with testosterone, resulting in the manufacture of hormone metabolites, such as estradiol and DHT.

    5-alpha-reductase

    • The enzyme 5-alpha-reductase is a critical enzyme that converts testosterone to dihydrotestosterone, or DHT. DHT is a more potent metabolite of testosterone and is known to lead to hair loss, as well as other side effects, including the aggravation of some forms of cancer. According to the study titled "Phytosterol feeding induces alteration in testosterone metabolism in rat tissues," published in the Journal of Nutritional Biochemistry in December 1998, phytosterols can inhibit 5-alpha-reductase, and can, in theory, reduce testosterone's effects on the body.

    Animal Studies

    • In the same study, titled "Phytosterol feeding induces alteration in testosterone metabolism in rat tissues," published in the Journal of Nutritional Biochemistry in December 1998, scientists conclude that dietary phytosterols fed to rats lowered the activities of the enzymes of testosterone metabolism. It must be noted, however, that the animals in the study were given fairly large doses of phytosterols.

    Human Studies

    • Unlike rat studies, research carried out with human subjects failed to record a significant effect of phytosterols on testosterone metabolism. A study published in the European Journal of Clinical Nutrition in May 2003, titled "Safety of long-term consumption of plant sterol esters-enriched spread," concluded that free and total testosterone levels in men were unaffected.

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