|If you do not like what you see, boys, you may already have taken too much testosterone reducing d-aspartic acid ;-)|
Now, I've been waiting for new evidence on what exactly DAA does ever since the corresponding study has been published; and, guess what, the waiting was rewarded last week with not just one, but two new studies on the effects of DAA in relevant subject groups.
- Study ä1: D-Aspartic acid sucks, big time (Melville. 2015, peer-reviewed) - As Melville et al. point out, there's abundant research on the hormonal effects of d-aspartic acid in rat models, but only limited research in humans.
"Previous research has demonstrated increased total testosterone levels in sedentary men and no significant changes in hormonal levels in resistance trained men. It was hypothesised that a higher dosage may be required for experienced lifters, thus this study investigated the effects of two different dosages of d-aspartic acid on basal hormonal levels in resistance trained men and explored responsiveness to d-aspartic acid based on initial testosterone levels" (Melville. 2015).To find out whether their hypothesis was correct, the researchers randomly assigned 24 males, with a minimum of two years’ experience in resistance training (age, 24.5 ± 3.2 y; training experience, 3.4 ± 1.4 y; height, 178.5 ± 6.5 cm; weight, 84.7 ± 7.2 kg; bench press 1-RM, 105.3 ± 15.2 kg) to one out of three groups who received (a) 6 g/d plain flour (D0), (b) 3 g/d of d-aspartic acid (D3), or (c) and 6 g/d of d-aspartic acid (D6).
Before the supplementation period, all participants performed a two-week training / supplementation washout period (to exclude effects of their previous training regimen and or supplement use) during which they trained on four days per week. The same standardized resistance training routine was continued through the experimental period (14 days), with participants consuming the supplement (or placebo) in the morning.
Figure 1: Changes in total and free testosterone in response to two weeks of std. training in conjunction with 3g or 6g d-aspartic acid per day or placebo supplement (Melville. 2015).
However, total testosterone was significantly reduced in the high dose D-aspartic acid group D6 (P = 0.03 | see Figure 1). Compared to the placebo group the D6 group exhibited significantly reduced free testosterone levels, as well. Since both effects were unrelated to the baseline testosterone levels (i.e. not just those with exceptionally high levels of T experienced a decline on DAA), this study clearly suggests that d-aspartic acid is not just useless as a testosterone booster, it's even worse than that: It reduces testosterone instead of boosting it!
- Study #2: D-aspartic acid rules, small time (LaMacchia. 2015, not peer-reviewed) - This study comes right from the University at Buffalo and information about the results is available only in form of an abstract to a talk the authors presented at an undergrad research meeting. What is still interesting about it, is the fact that LaMacchia et al. determined (for the first time) the effect of D-aspartic acid supplementation on athletic performance in young male athletes.
"After screening for ACSM low risk, 9 healthy male athletes (average age = 22y, body weight = 82.7 kg and body fat = 10.4%) were randomized to two groups for supplementation using a double blinded parallel arm experimental design. They ingested either 3 grams of d-aspartic acid (Aspartate, n=5) or a Placebo (n=4) for 14 days supplied in capsule form. Subjects recorded and replicated previous 3 day diets prior to testing.
Physical assessments were performed prior to and after supplementation included a peak VO2 test by cycle ergometer, 1 maximal repetition bench press and 1 maximal repetition squat (average values ±SD before supplementation were 41.7 ±6.4 ml/kg/min, 117.9 ±11.1 kg and 151.7 ±19.0 kg, respectively)" (LaMacchia. 2015).Now, in view of the results of the previously cited study by Melville, the results of LaMacchia's analysis of the performance data is surprising, to say the least:
"The Aspartate group improved performance in 1 maximal repetition bench press by 4.5 ±1.6kg (average ±SEM, p=0.03) and 1 maximal repetition squat by 8.2 ±3.8kg (average ±SEM, p=0.04). No change in performance measures were observed in the Placebo group. Body composition did not change for either group" (LaMacchia. 2015).The fact that the body composition didn't change appears to suggest that the beneficial effects on bench press and squat performance were not of hormonal origin. Rather than that, one may speculate that they were triggered by DAA's effect on the central nervous system (Fuchs. 2005). What is questionable, though, is whether these effects (assuming they actually exist) can outweigh the long(er)-term negative effects on testosterone Melville et al. observed in their study.
- Fuchs, Sabine A., et al. "D-amino acids in the central nervous system in health and disease." Molecular genetics and metabolism 85.3 (2005): 168-180.
- LaMacchia, Zach, Peter Horvath, and Brian Williams. "Effect of Aspartate Supplementation on Athletic Performance in Young Men." (2015).
- Melville, Geoffrey W., Jason C. Siegler, and Paul WM Marshall. "Three and six grams supplementation of d-aspartic acid in resistance trained men." Journal of the International Society of Sports Nutrition 12.1 (2015): 1-6.
- Willoughby DS, Leutholtz B. d-Aspartic acid supplementation combined with 28 days of heavy resistance training has no effect on body composition, muscle strength, and serum hormones associated with the hypothalamo-pituitary-gonadal axis in resistance-trained men. Nutrition Research, Available online 15 August 2013.