Dietary exposure to creatine-precursor amino acids in the general population

Abstract Background Creatine is a semi-essential nutrient that plays a critical role in energy metabolism, with dietary intake and endogenous synthesis contributing to overall creatine availability. While dietary creatine intake has been studied extensively, limited data exist on the dietary exposure to its precursor amino acids—glycine, arginine, and methionine—and their contribution to endogenous creatine synthesis. This study aimed to assess the dietary intake of these precursors in U.S. children and adults using data from the Third National Health and Nutrition Examination Survey (NHANES III) and to compare endogenous creatine synthesis with direct dietary creatine intake. Methods We analyzed NHANES III dietary recall data from 29,945 individuals aged 2 years and older. Intakes of glycine, arginine, methionine, and creatine were calculated per kilogram of body weight. The contribution of precursor amino acids to endogenous creatine synthesis was estimated using established metabolic conversion factors. Results The mean daily intakes of glycine, arginine, methionine, and creatine were 59.6 ± 0.4 mg/kg, 77.2 ± 0.5 mg/kg, 31.9 ± 0.2 mg/kg, and 15.5 ± 0.1 mg/kg, respectively. Estimated endogenous creatine synthesis from precursor amino acids was significantly greater than dietary creatine intake across all age groups ( P  < 0.01), with precursor-derived creatine production averaging 41.9 ± 0.3 mg/kg body weight per day, approximately 2.7 times higher than dietary creatine intake. Creatine precursor availability declined with age, with the lowest values observed in individuals aged ≥ 65 years. Conclusion This study provides the first comprehensive evaluation of total creatine availability in a representative U.S. population, highlighting the predominance of endogenous synthesis over direct dietary intake. These findings suggest that creatine metabolism is largely dependent on precursor amino acid intake and that certain populations, particularly older adults, may be at higher risk for reduced creatine availability. Future research should explore the physiological implications of these findings and potential dietary interventions to optimize creatine status across the lifespan.