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This morning, supplement researcher Richard Kreider, PhD, of Texas A&M University directed me to his study (1) involving a “purported aromatase and 5-alpha reductase inhibitor,” which turns out to have been fenugreek.

For 8 weeks, 30 young male subjects received either a capsule containing 500 mg of fenugreek or a placebo while following a supervised resistance exercise routine. The fenugreek extract was standardized for “grecunin” and supplied by Indus Biotech of India. To date, I have been unable to determine what grecunin is.

Over the course of the study, total and bioavailable (“free”) testosterone increased 6.57% and 12.26%, respectively, in the subjects taking fenugreek. Estradiol and DHT levels also increased (26.6% and 6.10%, respectively), though not significantly. No changes in hormone levels were found in the placebo group.

As explained in my recent post about boron, the enzyme aromatase converts testosterone into estradiol, whereas 5-alpha-reductase (5-AR) converts testosterone into DHT. Thus, you might think that because estradiol and DHT increased in this study, albeit not significantly, the fenugreek supplement didn’t work. The authors seemed to come to a different conclusion, stating, “estradiol decreased 9.64% from Week 0 to Week 4 before rising above baseline values by the conclusion of the 8-week study. Because of a significant increase in total and bioavailable testosterone without a corresponding [significant] increase in estradiol and DHT, we conclude that the [fenugreek extract] successfully, but incompletely, inhibited aromatase and 5-α reductase activity.”

The researchers also measured changes in body composition. While the fenugreek extract did not change fat-free mass, subjects receiving it did experience a reduction in fat mass of 1.77% vs. 0.55% in the placebo group. Granted, such changes may not be all that significant to you in the real world, but they were statistically significant here in the laboratory. The fenugreek supplement was found to have no significant effects on strength.

The authors drew an important conclusion, one worth keeping in mind when you walk through your local sports supplement store in search of a “testosterone booster”:

“AIs [aromatase inhibitors] marketed by nutritional supplement companies claim that these products increase androgen levels similarly to anabolic steroids while simultaneously suppressing estrogen levels. The current data, along with those from our previous work (Willoughby et al., 2007), support this notion to some extent, because we saw increases in total and bioavailable testosterone accompanied with minimal change in DHT and estradiol. Conversely, as our data suggest, an increase in endogenous testosterone levels does not always translate to an increase in muscle hypertrophy and strength. It is likely that the increase in endogenous testosterone levels from the experimental supplement did not affect androgen-receptor expression or the interaction between testosterone and an androgen receptor, which provides a possible explanation of why fat-free mass and strength did not increase more than in the PL group in our investigation. Thus, these data support the notion that elevated levels of testosterone within physiological levels have no influence on muscle strength in strength-trained young men.”


Most people taking a supplement like the one studied here will do so in the hope that it will provide not merely a change in testosterone, but also some downstream benefit: a change in body weight, body fat, muscle size, strength, libido, energy, mood, etc. What this study suggests is that supplementation with this particular fenugreek extract may allow young, healthy resistance-exercising males to lose slightly more body fat than would be the case if they took a placebo.


1. esnl.tamu.edu/Publications/Wilborn%20et%20al%20IJSNEM%202010.pdf