Short-term GAA loading: Responders versus nonresponders analysis

Dietary guanidinoacetic acid (GAA) has been suggested to be advantageous for favorable changes in tissue bioenergetics in terms of responder versus nonresponder performance, yet no studies so far explored the proportion of two distinct populations following short-term GAA intervention. A secondary analysis of previously completed guanidinoacetic acid (GAA) trials has been carried out in aim to classify individuals into responders and nonresponders using cut-off criteria for an increase in intramuscular creatine. A total of 30 individuals (mean age = 34.5 years, women 66.7%) who were supplemented with up to 3 g/day of GAA for at least 28 days with total muscle creatine evaluated using 1.5 T magnetic resonance spectroscopy studies were included in this examination. Pre-post measures included total creatine content (creatine plus phosphocreatine) determined from the quadriceps muscle, with participants were classified by arbitrary cut-off points in three categories, including responders (>10% increase in total creatine content at follow-up), quasi-responders (5%-10% increase), and nonresponders (<5% increase in total intramuscular creatine at postadministration). An average change in total creatine content after GAA supplementation was 22.9%, with 13.3% participants were categorized as nonresponders, 6.6% as quasi-responders, and 80.0% as responders (p < .001). A fairly high prevalence of individuals sensitive to dietary GAA advances this innovative agent as a rather effective tool to improve muscle creatine levels for at least 10% or more during 28-day loading.