Reference intakes of nutrients are the basis of nutritional research. The results of The Nutrition and Health Status Survey of Chinese Residents in 2002discovered that dietary reference intakes of protein in healthy adults were overestimated and need to be reevaluated. Methods 9healthy female adults received a restricted daily level of protein intake 0.75,0.82,0.89,0.97and 1.05g/(kg·d). Every dietary protein level lasted six days. On the sixth day, they took ¹³C-leucine as a tracer to carry out sTable isotope metabolic experiment. The kinetic parameters including leucine flow, oxidation rate and oxidate production rate were calculated. We applied biphasic linear regression crossover analysis on ¹³CO₂ data and protein intakes. We identified a breakpoint at the minimal rate of appearance of ¹³CO₂ expiration, specific to each level of dietary protein intake. [WT5"HZ]Results The Estimated Average Requirement (EAR) and the Recommended Nutrient Intake (RNI) of protein for healthy Chinese young female adults were determined to be 0.85and 0.97g/(kg·d). Conclusion According to the reference weight of female adults in recent national nutrition survey, we calculated that the daily protein recommended requirements for female adults was 55g, which was lower than current protein recommended requirements.