['Guanidinoacetic acid (GAA) is an experimental dietary additive that might act as a creatine source in tissues with high-energy requirements. In this case study, we evaluated brain levels of creatine in white matter, gray matter, cerebellum, and thalamus during 8\xa0wk oral GAA administration in five healthy men and monitored the prevalence and severity of side effects of the intervention.', 'Volunteers were supplemented daily with 36\xa0mg/kg body weight (BW) of GAA for the first 4\xa0wk of the intervention; afterward GAA dosage was titrated ≤60\xa0mg/kg BW of GAA daily. At baseline, 4, and 8\xa0wk, the participants underwent brain magnetic resonance spectroscopy, clinical chemistry studies, and open-ended questionnaire for side-effect prevalence and severity.', 'Brain creatine levels increased in similar fashion in cerebellum, and white and gray matter after GAA supplementation, with an initial increase of 10.7% reported after 4\xa0wk, and additional upsurge (7.7%) from the weeks 4 to 8 follow-up (P\xa0<\xa00.05). Thalamus creatine levels decreased after 4\xa0wk for 6.5% (P\xa0=\xa00.02), and increased nonsignificantly after 8\xa0wk for 8% (P\xa0=\xa00.09). GAA induced an increase in N-acetylaspartate levels at 8-wk follow-up in all brain areas evaluated (P\xa0<\xa00.05). No participants reported any neurologic adverse event (e.g., seizures, tingling, convulsions) during the intervention.'] Does dietary guanidinoacetic acid increase brain creatine levels in healthy men?