Introduction: Beta-alanine (BA) is a popular ergogenic supplement because it can induce muscle carnosine loading. We hypothesize that, by analogy with creatine supplementation, 1) an inverse relationship between urinary excretion and muscle loading is present, and 2) the latter is stimulated by carbohydrate- and protein-induced insulin action.
Methods: In study A, the effect of a 5-wk slow-release BA (SRBA) supplementation (4.8 g·d−1) on whole body BA retention was determined in seven men. We further determined whether the coingestion of carbohydrates and proteins with SRBA would improve retention. In study B (34 subjects), we explored the effect of meal timing on muscle carnosine loading (3.2 g·d−1 during 6–7 wk). One group received pure BA (PBA) in between the meals; the other received PBA at the start of the meals, to explore the effect of meal-induced insulin release. Further, we compared with a third group receiving SRBA at the start of the meals.
Results and Conclusion: Orally ingested SRBA has a very high whole body retention (97%–98%) that is not declining throughout the 5-wk supplementation period, nor is it influenced by the coingestion of macronutrients. Thus, a very small portion (1%–2%) is lost through urinary excretion, and equally only a small portion is incorporated into muscle carnosine (∼3%), indicating that most ingested BA is metabolized (possibly through oxidation). Second, in soleus muscles, the efficiency of carnosine loading is significantly higher when PBA is coingested with a meal (+64%) compared with in between the meals (+41%), suggesting that insulin stimulates muscle carnosine loading. Finally, the chronic supplementation of SRBA versus PBA seems equally effective.