Evaluation of the Protein Requirement in Chinese Young Adults Using the Indicator Amino Acid Oxidation Technique

Objective To accurately calculate the protein requirements in Chinese young adults using the indicator amino acid oxidation technique. Methods Nine women and ten men received a restricted daily level of protein intake (0.75, 0.82, 0.89, 0.97, and 1.05 g/kg), along with L-[1-C-13]-leucine. Subjects' protein requirement was determined by a biphasic linear regression crossover analysis of (FCO2)-C-13 data. In doing so, a breakpoint at the minimal rate of appearance of (CO2)-C-13 expiration specific to each level of dietary protein was identified. This trial was registered with the Chinese clinical trial registry as ChiCTR-ONC-11001407. Results The Estimated Average Requirement (EAR) and the Recommended Nutrient Intake (RNI) of protein for healthy Chinese young adults were determined to be 0.87 and 0.98 g/(kg.d), respectively, based on the indicator amino acid oxidation technique. Conclusion The EAR and RNI of mixed protein are 5% and 16% that are lower than the current proposed EAR and RNI (0.92 and 1.16 g/(kg.d), respectively), as determined by the nitrogen balance method. The respective EAR and RNI recommendations of 0.87 and 0.98 g/(kg.d) of mixed protein are estimated to be reasonable and suitable for Chinese young adults.