Wednesday, December 14, 2016

Meta-Analysis: Could Energy Drinks be All About Taurine? Taurine, not Caffeine Predicts Performance Enhancement

While almost all energy drinks appear to have it, the evidence that taurine adds to the effects of caffeine has hitherto been unconvincing. Does this change with the latest study by a group of researchers from Brazil and Spain?
Energy drinks (ED) are all about caffeine, right? I have to admit. If you had asked me before I've read the latest study from the Londrina State University in Brazil and the Camilo José Cela University in Spain, I would have answered this question in the affirmative. I mean, come on... the strange add-ons the producers mix into their drinks have but one purpose: distinguish drink X from drink Y and, even more importantly, the healthier competition of plain coffee.

The fact that Souza, et al. observed in their latest meta-analysis that "a signifcant association between taurine dosage (mg) and performance (slope = 0.0001; p = 0.04), but not between caffeine dosage (mg) and performance (slope = 0.0009; p = 0.21)," caught my attention.
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Before we discuss how relevant this result of the authors' meta-regression actually is, it would be prudent to take a brief look at the methodology section of the paper: As you would expect, the scientists performed a systematic review and meta-analysis of published prior to January 2016 disregarding: (1) case reports; (2) review articles; (3) the use of drugs/substances which influ enced the outcome; (4) caffeine use without ED; (5) ED use without caffeine; (6) subjects on energy-restricted diets and/or weight reduction programs; (7) articles with animal models; (8) studies with samples that were ill or had physical limitations for exertion; (9) longitudinal studies.

Eventually N=34 articles that were (1) original; done with healthy adults; (2) reported the caffeine dose in the ED; (3) measured of physical performance pre- and post-intervention; (4) had a placebo group/session; (7) and offered enough data for effect size calculation were included in the scientists' statistical analysis.
Figure 1: Effects on endurance (left) and jumping (right) performance according to meta-analysis (Souza. 2016).
As you can see in Figure 1, the ED ingestion improved both, the subjects' performance in standardized endurance (ES = 0.53; p < 0.001 | Figure 1, left) and jump tests (ES = 0.29; p = 0.01 | Figure 1, right). Likewise beneficial were
  • the effects on muscle strength and endurance (ES = 0.49; p < 0.001), and 
  • sport-specifc actions (ES = 0.51; p < 0.001; cf. Table 1).
What did not improve, however, are the subjects' sprinting times - well, at least not significantly across the N=17 studies (ES = 0.14; p = 0.06).
Note: This article does not say that caffeine doesn't work! That caffeine works is beyond doubt. What the article does claim, however, is that the results of the meta-analysis, when combined with previous research, suggest that the ratio of caffeine to taurine could explain differences between the efficacy of various drinks (see bottom line for further discussion).
With a borderline significant effect and an increase of 16% in a study by Alford, et al., I would not discount the possibility that EDs would help Usain Bolt, as well.
Table 1: Subgroup analyses of categorical variables (Souza. 2016).
But didn't we want to talk about something else... oh, yes: the role of taurine! I guess some of you are already rolling their eyes. After all, I make no bones about my personal assessment that taurine may indeed be one of the most underrated amino acid supplements on the market (learn more).
Figure 2: Illustration of the subject- and supplement dependent continuous variables and their impact on the effect size indicated by the slope and significance of the results of the meta-regression (Souza. 2016).
So what's the evidence, then? Well with p-value of 0.04, taurine is the only subject / supplement related continuous variable that predicted the performance increase that was observed in the studies. The slope and thus the increase in effect size per unit of taurine in the corresponding meta-regression was however hardly relevant. No wonder, after all, previous studies, as well as the suspected stress-protective as well as anti-protein catabolis mechanisms (Zhang. 2004; HaeMi. 2003) suggest that taurine will have chronic rather than acute effects (cf. Rutherford. 2010); with the studies in this review being acute supplementation studies, these benefits couldn't be recorded, anyways.
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So, this begs the question: Even if the advantage is small, why could more taurine yield a higher exercise performance? Unfortunately, the authors didn't address this question in detail, but hey, I guess otherwise I would be useless... Now, I cannot tell you for sure what it is and without having access to the full dataset I cannot even confirm my hypothesis, but I still feel reminded of an older article I wrote about the synergy of caffeine and taurine, in which I presented evidence that a 1:10 mix of caffeine to taurine may be the optimal compromise between the jittery energy spike from caffeine and the calming (GABA mediated | Ripps. 2012) effects of taurine.

If we take a look at the continuum of caffeine and taurine intakes in the studies in the meta-analysis at hand, it turns out that - with caffeine dosages ranging from 40 and 325 mg and amount of taurine ranging from 71 to 3105 mg - many of the studies ended up being in that range.

If someone would now correlate the effect sizes and the caffeine:taurine ratio and find that there is a significant relationship between the two, this would provide more evidence that the implications I've formulated based on animal studies in 2013 (read the original article) could inform your supplement and dosing choices, so that 200-400 mg caffeine and 2,000-4,000 mg of taurine make a highly effective stack. As previously pointed out (see red box), this does not imply that caffeine alone wouldn't work, but having it with taurine in the correct ratio may be what makes one energy drink more effective than the other | Comment on Facebook!
  • Alford, Chris, Harriet Cox, and Robert Wescott. "The effects of red bull energy drink on human performance and mood." Amino acids 21.2 (2001): 139-150.
  • HaeMi, Lee, Paik IlYoung, and Park TaeSun. "Effects of dietary supplementation of taurine, carnitine or glutamine on endurance exercise performance and fatigue parameters in athletes." Korean Journal of Nutrition 36.7 (2003): 711-719.
  • Ripps, Harris, and Wen Shen. "Review: taurine: a “very essential” amino acid." (2012).
  • Rutherford, Jane A., Lawrence L. Spriet, and Trent Stellingwerff. "The effect of acute taurine ingestion on endurance performance and metabolism in well-trained cyclists." International journal of sport nutrition 20.4 (2010): 322.
  • Souza, Diego B., et al. "Acute effects of caffeine-containing energy drinks on physical performance: a systematic review and meta-analysis." European journal of nutrition (2016): 1-15.
  • Zhang, M., et al. "Role of taurine supplementation to prevent exercise-induced oxidative stress in healthy young men." Amino acids 26.2 (2004): 203-207.