Eating or supplementing with garlic has many claimed benefits, one which is increased testosterone levels. While human research is lacking in this area, the effect of garlic on testosterone production in rats has been studied.
A 4-week study done in 2001 had some promising results. Both the control group and the experimental group of rats were fed high protein diets consisting of either 40, 25, or 10 g of protein per 100 g of body weight and 5 g of fat per 100 g of body weight. The experimental group also took in 8 g of a garlic powder supplement per kg of body weight, while the control group received no garlic powder.
At the end of the four weeks, the rats were examined, and the results were:
“testicular testosterone content, urinary 17-ketosteroid content, arginase activity in the liver and nitrogen balance were significantly increased in rats after garlic supplementation to the 40% casein diet, whereas plasma corticosterone concentration was significantly decreased in rats after garlic supplementation to the 40 or 25% casein diet. Based on urinary excretion of creatinine data, body muscle mass was not affected by garlic supplementation. However, nitrogen balance data suggested that nitrogen retention in the body was enhanced by garlic supplementation in rats fed a high protein diet. Similarly, hepatic arginase activity data suggested that protein synthesis in the liver was enhanced by garlic supplementation in rats fed a high protein diet. Urinary 17-ketosteroid is an index of steroid hormone secretion, which is derived almost completely from testosterone secretion in the whole body (i.e., an index of testosterone secretion in testis). These results suggest that protein anabolism occurs in rats fed the high protein diet supplemented with garlic. Concerning the effects of garlic on protein metabolism, the different responses to garlic supplementation in rats fed normal-fat diets with different protein levels suggest that protein anabolic effects were induced by the high protein diet (40% casein diet), but not by the low protein diet (10% casein diet). The present study suggests that to induce the protein anabolic effect of garlic supplementation, the protein content in the diet should be high. Therefore, our findings suggest that protein anabolic effects were induced to a greater extent by garlic supplementation in rats fed the high protein experimental diet.” (pg. 2154-2155)
Urinary secretion of 17-ketosteroid increased by about 30% in the 40 g protein/100 g body weight experimental group, which indicates a significant rise in testosterone production.
What Does This Mean?
The experimental group of rat experienced an increase in testosterone production and nitrogen retention. The rats eating the highest protein diet experienced these effects to the greatest extent.
How well these results translate to humans is debatable, and 8 g of garlic per kg body weight is an extremely high dose. Garlic supplements may be proven to boost testosterone in rats, but I would not bet on it for making any significant difference when it comes to human supplementation at a more reasonable dose.
Oi Y, Imafuku M, Shishido C, Kominato Y, Nishimura S, & Iwai K. (2001). Garlic supplementation increases testicular testosterone and decreases plasma corticosterone in rats fed a high protein diet. The Journal of Nutrition. 131(8), 2150-6.