Obligatory urinary and fecal nitrogen losses in young women, older men, and young men and the factorial estimation of adult human protein requirements.
Obligatory urinary and fecal nitrogen losses and urinary urea nitrogen and creatinine excretion levels were determined in 11 young women (four of whom used oral contraceptives), eight older men, and five young men. Values for obligatory nitrogen losses in the young women who did not use oral contraceptives were similar to those observed previously in young women and lower than those reported for young men. Our values for older men were lower than previously reported values for obligatory losses observed in young and elderly men, but similar to previously reported values for young women and to values for our women who did not use oral contraceptives. The four oral contraceptive users had significantly higher levels of total urinary and fecal obligatory nitrogen losses than the nonusers in our study. When values from our study and values from other recent studies are considered, variations in obligatory nitrogen losses appear to be larger among individuals within an age-sex group than the observed differences between groups. When the intakes of protein recommended as safe by the Food aculated from obligatory nitrogen losses per se, the recommended levels appear to be only marginally adequate.