Examination of Chinese Habitual Dietary Protein Requirements of Chinese Young Female Adults by an Indicator Amino Acid Method

Objective: To determine protein requirement of Chinese young female adults on habitual Chinese diet through indicator amino acid oxidation (IAAO) technique. Design: Twenty women with a mean (SD) age of 21.6 (0.9) years were healthy based on questionnaire, physical examinations and screening tests. There were three consecutive periods of 7 days each with six different intakes of protein (0.70, 0.78, 0.86, 0.94, 1.02 and 1.10 g/kg．d) within Chinese habitual diets (proportions of good-quality protein were 40 to 45%). Subjects were randomly allocated equally into two groups (1.10, 0.86, 0.78 g/kg．d for group 1 and 1.02, 0.94, 0.70 g/kg．d for group 2 from period 1 to period 3 in turn). Adaptation days were from day 1 to day 6 and the isotope study day was day 7 in each period. Amino acid kinetics was measured in non-menstrual periods, based on the IAAO technique. Two indicators (rate of release of 13CO2 and rate of leucine oxidation) were used to estimate protein requirement by breakpoint analysis with a two-phase linear regression crossover model. Results: Mean and population safe protein requirements of Chinese habitual diets in non-menstrual periods from the rate of release of 13CO2 were 0.91 and 1.09 g/kg．d, respectively. And from the rate of leucine oxidation were 0.92 and 1.10 g/kg．d, respectively. Conclusions: The protein requirement of young women on Chinese habitual diets in non-menstrual period was lower than the current protein reference intake for Chinese females. Further studies are necessary to explore female protein requirements during the whole menstrual cycle.