Effects of a purported aromatase and 5 α-reductase inhibitor on hormone profiles in college age men
Journal Title (Medline/Pubmed accepted abbreviation):   Int J Sports Nutr Exerc Metab
Year: 2010
Volume: 20
Number: 6
Page numbers: 457-465
doi (if applicable): N/A

Summary of Background and Research Design

Background:T estosterone levels are related to many physiologic conditions such as protein synthesis, muscle strength, fat oxidation, and adiposity. Therefore, research into improving exercise performance has focused on supplementation with testosterone precursors or derivatives to increase the levels of free testosterone. However, an alternative approach is to reduce testosterone breakdown by inhibiting the enzymes responsible (aromatase and 5-α-reductase). Evidence from aromatase inhibitor (AI) studies suggest that anabolic benefits may be obtained, although it is uncertain to what extent the testosterone increase is necessary to achieve a performance benefit.

Hypothesis/purpose of study:To determine the effects on strength, body composition, and hormonal profiles of fenugreek (Trigonella foenum-graecum [standardized for Grecunin]), which may inhibit aromatase and 5-α-reductase activity

Subjects:30 resistance-trained (> 1 year of total-body resistance training) males were randomized to placebo (n = 13; age, 21 ± 3 yr; height, 180 ± 6.4 cm; weight, 84 ± 15 kg; body fat, 18.3% ± 6.8%) or fenugreek (n = 17; age, 21 ± 2.8 yr; height, 178 ± 5.8 cm; weight, 85 ± 9.6 kg; body fat, 18.8% ± 4.8%).

Experimental design: Randomized, double-blind, weight-matched, parallel-group study

Treatments and protocol:Participants were divided into 2 groups based on weight; members of each group were randomized to 500 mg of placebo or fenugreek. Participants performed 4 exercise sessions: practice, baseline (T1), and 2 experimental after 4 (T2) and 8 (T3) weeks of supplementation. Each session consisted of a 1-repitition maximum (1RM) upper and lower body exercise preceded by a warm-up and a 10-minute rest. This was followed by a 15-minute rest and a Wingate anaerobic capacity test. A resistance training program for upper and lower body was detailed for each participant during supplementation. Blood samples were drawn at all testing for chemistry and hematology profiles and levels of anabolic hormones. Side effects and health status were determined weekly.

Summary of research findings:
  • No major clinical side effects were reported during the study; a few cases of gastrointestinal discomfort occurred.
  • There were no significant group × time interactions or main time effects for the chemistry, hematology, renal function, or muscle damage parameters.
  • There were no significant group × time interactions for bench- and leg-press, muscle endurance, anaerobic capacity, or mean power between the treatment groups.
    • There was a significant main time effect for bench- and leg-press (P < .001 and P < .001, respectively) in the fenugreek and placebo groups.
  • There was a significant main time effect for total body weight and fat-free mass (P = .034 and P < .001, respectively) in the fenugreek and placebo groups
    • There were no significant between-group differences (P = .083).
  • There were significant group × time interactions (P = .048) and main time effects (P = .001) for body fat percentage in the fenugreek and placebo groups.
    • The mean body fat percentages of the subjects in the fenugreek group for T1, T2, and T3 were 18.87% +⁄- 4.87%, 17.91% +⁄- 4.98%, and 17.82% +⁄- 5.04%, respectively. By contrast, the body fat percentages of the placebo subjects for T1, T2, and T3 were 18.37% +⁄- 6.35%, 17.59% +⁄- 7.04%, and 17.82% +⁄- 7.19%, respectively.
      • NOTE: The % body fat data in Figure 1 would be more correctly reported as the decrease, rather than change, in % body fat on the vertical axis label. As it appears, the figure indicates an increase in % body fat in both groups, which is at odds with the text of the Results section.
    • There were no reported group × time interactions for fat-free mass (significant time effect only) or fat mass.
  • There were significant group × time interactions for total testosterone (P = .018) and bioavailable testosterone (P = .049), but not free testosterone (P = .90) or dihydrotestosterone (P = .422), between the fenugreek and placebo groups.
    • Total and bioavailable testosterone levels increased slightly in the fenugreek group and decreased in the placebo group.

Interpretation of findings/Key practice applications:

The results showed that fenugreek did not completely block aromatase and 5-α-reductase activity because total and bioavailable testosterone increased without a corresponding increase in its breakdown product dihydrotestosterone. Although fenugreek had no effect on fat-free mass, body fat percentage was significantly reduced. It is unclear why the authors did not report any data on changes in fat mass. There may be a relationship between androgen levels and adiposity; however, this study did not measure lipolysis markers. Total and bioavailable testosterone levels did increase to a very small degree (< 5 ng/mL on a mean basis for each) with fenugreek supplementation, but this did not translate into increased muscle strength. Higher levels of total or bioavailable testosterone than those observed in this study are necessary to increase muscle strength.
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