Human skeletal muscle has large capacity to increase carnosine content in response to beta-alanine supplementation: a systematic review with Bayesian individual and aggregate data E-Max model and meta-analysis.

Beta-alanine (BA) supplementation increases muscle carnosine content (MCarn) and is ergogenic in many situations. Currently, many questions on the nature of the Mcarn response to supplementation are open, and the responses to these have considerable potential to enhance the efficacy and applications of this supplementation strategy. The objective of this study was to conduct a Bayesian analysis of available data on the Mcarn response to BA supplementation. A systematic review (with meta-analysis) of individual and published aggregate data was conducted, using a dose response (Emax) model. The protocol was designed according to PRISMA guidelines. A three-step screening strategy was undertaken in order to identify studies that measured the Mcarn response to BA supplementation. In addition, the research analysed individual data from five separate studies, conducted in the authors' laboratory. Data were extracted from all controlled and uncontrolled supplementation studies conducted on healthy humans. Meta-regression was used to consider the influence of potential moderators on the primary outcome, including dose, sex, age, baseline Mcarn and analysis method used. The Emax model indicated that human skeletal muscle has a large capacity for non-linear Mcarn accumulation and that commonly-used BA supplementation protocols may not come close to saturating muscle carnosine content. Neither baseline values nor sex appear to influence subsequent response to supplementation. Analysis of individual data indicated that Mcarn is relatively stable in the absence of intervention, and effectually all participants respond to BA supplementation (99.3% response [95%CrI: 96.2 –100])

Dietary β-alanine intake assessed by food records does not associate with muscle carnosine content in healthy, active, omnivorous men and women.

β-alanine (BA) is one of the most widely used sport supplements, due to its capacity to improve high intensity exercise performance by increasing muscle carnosine (MCarn) content, and consequently, the buffering capacity of the muscle. BA is also available in a variety of animal foods, but little is currently known about the influence of dietary BA intake on MCarn. The aim of the current study was to compile a detailed summary of available data on the BA content of commonly consumed foods, and to explore whether associations could be detected between self-reported dietary BA intake and skeletal MCarn in a group of 60 healthy, active, omnivorous men and women. Dietary BA intake was assessed via 3-day food records and MCarn content assessed by high performance liquid chromatography. A series of univariate and multivariate linear regression models were used to explore associations between estimated dietary BA and MCarn. No evidence of associations between dietary BA intake and MCarn were identified, with effect sizes close to zero calculated from models accounting for key demographic variables (f2 ≤ 0.02 for all analyses). These findings suggest that capacity to increase MCarn via dietary strategies may be limited, and that supplementation may be required to induce increases of the magnitude required to improve performance