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.
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).
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.
References:

• 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.