Hi Pro Pam,
I’ve been reading a bit about the effect of cycling on lower testosterone levels in men—and there appears to be a very real negative relationship. There also seems to be some evidence that nutritional supplementation (with BCAA among other things) may combat this. Could you comment on this phenomenon and your take on the capacity for nutrition to combat this?
Anyone who has paid attention to the recent confessions of the use of performance-enhancing drugs in professional cycling would have to conclude that low testosterone is rampant among cyclists. However, the data suggest that if cycling does in fact lower testosterone, the condition is neither as serious nor as pervasive as one might suspect based on the popularity of testosterone patches in the pro peloton. Testosterone acts on many target organs, and some of its effects are certainly relevant to athletic performance: it stimulates protein synthesis/inhibits degradation in skeletal muscle and acts on bone marrow to increase production of red blood cells by a mechanism that is apparently independent of EPO. Thus, it is obvious why low testosterone would be a concern to any athlete.
A handful of studies have looked at whether cyclists have lower testosterone than other athletes or non-athletes, with mixed results. One study reported lower testosterone in amateur road cyclists than in competitive weight lifters and non-athletes. Several years ago, in a study that included some of the cyclists in the BOCOMO peloton, we compared the hormonal profiles of cyclists, runners, and resistance-trained athletes. We found no differences in testosterone among recreationally competitive cyclists, runners, and resistance-trained athletes. It is important to note that there are no reports of clinically low testosterone in male cyclists. Even the studies that found cyclists had lower testosterone than other athletes or non-athletes reported the cyclists’ testosterone to be well within the normal range.
This observation raises an important practical question: if testosterone is reduced, but still “normal,” will skeletal muscle protein synthesis or red blood cell production be negatively impacted? One study provides some insight into this issue. Seven recreationally competitive male cyclists (mean VO2 max 56 ml O2/kg/minute) participated in 4 weeks of high-intensity training that consisted of 2 interval sessions in the lab each week: 5–8 repetitions of 5 minutes at 80% of peak power output; and 2 repetitions of 5 km at 90% of 5-km time trial speed. After the 4 weeks of high-intensity training, testosterone decreased, but was well within the normal range. However, despite the decline in testosterone, performance (peak power output, as well as time in 5- and 40-km time trials) significantly improved. Other studies have reported that changes in skeletal muscle mass or strength are not proportional to changes in testosterone. Taken together, these results suggest that if testosterone is within the normal range, performance gains still occur. However, although it is not clear if low (but normal) testosterone limits performance gain, there are nutritional strategies to counteract reductions associated with endurance exercise.
To identify dietary means to maintain testosterone production, we have to look briefly at the process of testosterone production and how it is regulated. Believe it or not, testosterone production begins in the brain—in the hypothalamus, to be exact. The hypothalamus releases a hormone that acts on the pituitary to release other hormones that stimulate testosterone production in the testes. The reduction in testosterone observed in cyclists and other endurance athletes (e.g., distance runners) likely occurs due to down-regulation by the hypothalamus as a result of negative energy balance or the physiologic stress of exercise. The hypothalamus can detect whole-body energy status, and when energy expenditure is high relative to dietary energy intake, it suppresses energy-consuming processes, such as protein synthesis, red blood cell production, and reproduction. Other anabolic hormones besides testosterone, such as thyroid hormone and growth hormone/insulin-like growth factor (GH/IGF), are also reduced by hypothalamic control during low energy availability. The physiologic stress of high-volume/high-intensity exercise, resulting in increased levels of the stress hormone cortisol, may also suppress testosterone production at the level of the hypothalamus.
An obvious way to prevent the reduction in testosterone that might occur with high-volume training is to consume adequate dietary energy. Of course, for cyclists and other endurance athletes who are obsessed with the “power-to-weight” ratio, this presents a conundrum. Achieving minimal body fat (< 10%) will likely result in reduced testosterone, as well as reductions in other anabolic hormones. As a general guideline, endurance athletes should consume 6–10 g of carbohydrate/kg of body weight/day and 1.6–1.7 g of protein/kg of body weight/day with no less than 20% of energy from dietary fat. For a 70-kg cyclist, this equates to 420–700 g of carbohydrate, 112–120 g of protein, and 60–90 g of fat for a total of about 2700–4100 kcal. In particular, sufficient dietary protein has been shown to prevent the decline in testosterone and the increase in cortisol observed following high-intensity resistance training in participants with suboptimal protein intake (~ 0.7 g/kg of body weight/day). In summary, adequate dietary energy and protein can combat the reduction in testosterone that occurs with high-volume/intensity endurance training.
Dr. Pam Hinton is an associate professor of Nutrition and Exercise Physiology at the University of Missouri–Columbia where she teaches Sports Nutrition and studies the effects of energy balance on bone health. Check out her full bio for more information. If you have a nutrition-related question, send it to Pro Pam.