by Thomas Incledon, PhD(c), RD, LD/LN, RPT, NSCA-CPT, CSCS
Back around September 1996, Muscle and Fitness ran on an article on the benefits of Tribulus. Prior to this few Americans knew of Puncture Vine, more commonly known by its Latin name, Tribulus terrestris. Since the mid’90s Eastern European world-champion and Olympic strength and power athletes claimed the herb could build muscle by increasing testosterone production. Today a bunch of supplement companies still claim that this stuff works even though they can’t provide any real proof. Arguments for the herb’s effectiveness are based largely on a few inadequate studies and traditional use. Ancient Greeks used it as a diuretic, a mild laxative and a general tonic. Ayurvedic physicians have long valued the plant for its diuretic properties as well as its aphrodisiac qualities and include it in rejuvenative formulations for treating sexual problems. In China, the herb is frequently used to treat a variety of diseases affecting the liver, kidneys, urinary tract (including urolithiasis, or urinary stones) and cardiovascular system. Cross-culturally, Tribulus is most often used to treat infertility, impotence and libido problems. The herb contains the steroidal saponins terrestrosin, dioscin, gracillin, kikuba saponin, protodioscin, neohecogenin glucoside and tribulosi. According to one paper, the saponins may be responsible for the herb’s aphrodisiac properties [1].
Scientists at the Chemical Pharmaceutical Research Institute in Sofia, Bulgaria investigated the effects of Tribulus in the 1970s. Based on the study results, Eastern European drug companies began releasing standardized Tribulus preparations to treat sexual disorders as early as 1981. The Bulgarian study, now out of print but often cited by supplement makers, demonstrated that Tribulus boosted blood levels of luteinizing hormone, a pituitary hormone responsible for regulating testosterone levels. Luteinizing hormone “turns on” natural testosterone production in humans. Researchers didn’t study muscle strength, however. Because the study is out of print, it is impossible to verify important details such as how much luteinizing hormone levels increased and whether it increased testosterone.
Another study, first published in the Russian journal Farmatsiya and mentioned in the 1996 Muscle and Fitness article by James Wright, reported that 750 to 1,500 mg oral doses of Tribulus administered daily for 30 to 60 days increased testosterone levels of men suffering from impotence and infertility [2] The increase was not clinically significant and, again, researchers were studying only whether testosterone levels increased. They did not examine changes in muscle strength.
Some supplement company researchers are concluding that Tribulus can influence muscle strength based on the Bulgarian and Russian studies. The problem with making this jump is that it is unclear how long either luteinizing hormone or serum testosterone was elevated and how much variation occurred among study subjects. That is, did some men’s levels increase a lot while others increased only a little? Did they all increase to the same extent? Unless an individual reaches pharmacological or above-normal levels of serum testosterone, increases in testosterone after taking Tribulus may be meaningless. Thus, Tribulus may lack the physiological punch to have a significant, long-term effect on testosterone levels. To put it into perspective, serum testosterone levels also rise after a hard sprint workout or a weight session in the gym.
To get around this enormous obstacle, manufacturers are combining Tribulus with other hormone supplements that purportedly enhance testosterone production. The steroid precursors DHEA (dehydroepiandrosterone) and androstenedione are promoted as testosterone enhancers, but they work differently than Tribulus. Both DHEA and androstenedione provide the raw material for testosterone formation, while, as mentioned previously, Tribulus increases luteinizing hormone levels and therefore may affect testosterone production. Assuming a combination of the three works better than any one ingredient on its own, several supplement companies are producing “stacked” products that combine DHEA, androstenedione and Tribulus. The manufacturers claim that each compound’s testosterone-inducing effects have been studied separately and have all been shown to potentiate testosterone production to varying degrees and by various mechanisms. DHEA and androstenedione are potent male hormones, and people should be cautious about using them. Anyone taking either DHEA or androstenedione should have regular blood tests and discuss the therapy with a health care provider. The assumption that DHEA, androstenedione and Tribulus are effective training aids for bodybuilding and fitness training is, at this point, sheer speculation. Various studies and abstracts presented at annual meetings indicate that different Tribulus supplements do not elevate testosterone either separately [3] or with vitamins and minerals [4] or in conjunction with prohormones [5, 6].
In one study, the effects of the herbal preparation Tribulus terrestris on body composition and exercise performance were investigated using resistance-trained men. Fifteen subjects were randomly assigned to a placebo or Tribulus (3.21 mg per kg body weight daily) group. Body weight, body composition, maximal strength, dietary intake, and mood states were determined before and after an 8-week periodized resistance training and supplementation period. There were no changes in body weight, percentage fat, total body water, dietary intake, or mood states in either group. The researchers concluded that supplementation with Tribulus does not enhance body composition or exercise performance in resistance-trained men [3]. In another study that investigated the effects of Tribestan (the Bulgarian Tribulus preparation) with vitamins and minerals found no effects on testosterone levels in healthy men [4]. Probably the strongest death blow to Tribulus are the studies combining it with prohormones [5, 6]. The effects of androgen precursors, combined with herbal extracts designed to enhance testosterone formation and reduce conversion of androgens to estrogens were studied in young men. Subjects performed 3 days of resistance training per week for 8 weeks. Each day during Weeks 1, 2, 4, 5, 7, and 8, subjects consumed either placebo or a supplement, which contained daily doses of 300 mg androstenedione, 150 mg DHEA, 750 mg Tribulus terrestris, 625 mg Chrysin, 300 mg Indole-3-carbinol, and 540 mg Saw palmetto. The results provided evidence that the addition of the herbal extracts to androstenedione does not result in increased serum testosterone concentrations, reduce the estrogenic effect of androstenedione, and did not augment the adaptations to resistance training [5]. Another study by the same research group also found that Tribulus did not work in older men [6].
However, a review paper claims that the active ingredient of Tribulus is protodioscin (Adimoelja, 2000). Protodioscin is supposed to be converted into DHEA and also stimulate sexual desire. DHEA itself is not a good testosterone precursor. However, protodioscin can stimulate erectile function in rabbits (Adaikan, et al. 2000). It wouldn’t be that far of a stretch to say that if athletes ingesting high doses of Tribulus are more easily aroused, they may assume it is due to higher testosterone levels. If they become more sexually active, it may simply reinforce their belief. The protodioscin content of Tribulus can vary considerably depending on various conditions such as location, harvesting, weather, processing, packaging, and storage. Future studies should test the protodioscin content of a Tribulus product before giving it to subjects to validate it has the active ingredient.
The bottom line? Despite the anecdotes, there is no conclusive evidence that Tribulus enhances muscle growth or strength. For now, it is merely a fad. More research must be conducted on healthy people who have no libido or hormonal problems to see if Tribulus truly affects muscle. It must be evaluated both as a stand-alone supplement and in combination with other supplements. And finally, the study results must be peer-reviewed.
References
1. Yan, W., et al., Steroidal saponins from fruits of Tribulus terrestris. Phytochemistry, 1996. 42(5): p. 1417-1422.
2. Wright, J., A Natural Wonder, in Muscle & Fitness. 1996. p. 140-142.
3. Antonio, J., et al., The effects of Tribulus terrestris on body composition and exercise performance in resistance-trained males. International Journal of Sport Nutrition & Exercise Metabolism, 2000. 10(2): p. 208-215.
4. Taskov, M., S. Milano, and A. Maleova, Vitaton: Effect on the concentration of some hormones in the serum of healthy subjects. MBI. Medico-Biologic Information, 1988(1): p. 24-26.
5. Brown, G.A., et al., Effects of anabolic precursors on serum testosterone concentrations and adaptations to resistance training in young men. International Journal of Sport Nutrition & Exercise Metabolism, 2000. 10(3): p. 340-359.
6. Brown, G.A., et al., Endocrine and lipid responses to chronic androstenediol-herbal supplementation in 30 to 58 year old men. Journal of the American College of Nutrition, 2001. 20(5): p. 520-528.
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