Gamma Oryzanol ("Gamma-O") is a highly lipophilic sterol-like compound extracted from rice bran oil. It is used in various supplements with the belief that it increases testosterone by elevating Luteinizing Hormone (LH).
Evidence that it increases Testosterone or LH
In 1997, a placebo-controlled study was performed that examined gamma oryzanol supplementation in resistance trained men (1). The treatment group received 500 mg of gamma oryzanol for 9 weeks. Tested variables were 1 repetition max's of bench press and squat, as well as vertical jump power. No differences were seen between groups (placebo vs. gamma oryzanol). They also tested various laboratory parameters including testosterone, estrogen, cortisol, and cholesterol ratios. Again, no differences between groups were seen.
Is Lipophilicity a Problem?
Could lack of absorption be the reason why Gamma Oryzanol failed to effect testosterone and muscular strength in men? One of the most recent companies to market this product claims this is indeed the case. As a highly lipophilic compound, Gamma Oryzanol would need to be properly emulsified for gastrointestional absorption. A 1991 study found <5% absorption of phytosterols similar to gamma oryzanol when fed to rats by mouth (2). In order to circumvent the absorption problem, they then administered gamma oryzanol to rats through IV (intravenous) or subq (subcutaneous) and examined its effects on Luteinizing Hormone, and Growth Hormone (GH). Unexpectedly, they found that Gamma Oryzanol actually decreased LH, and GH. Interestingly, it also decreased the release of various catecholamines, including dopamine. The authors concluded:
"Although it hasn't been directly measured, this metabolic milieu...may actually reduce testosterone production."
- Gamma Oryzanol does not increase testosterone, or increase muscular strength in humans
- In rats, IV or subq administration actually decrease testosterone and growth hormone
- Its lack of absorption is probably a good thing