A Study of the Endogenous Nitrogen Output of College Women, with Particular Reference to Use of the Creatinine Output in the Calculation of the Biological Values of the Protein of Egg and of Sunflower Seed Flour

Data from studies during three consecutive years have been combined in a study of the endogenous metabolism of women 19 to 30 years of age. Twenty-five subjects participated in the entire study. In addition, biological values were determined for sunflower seed flour and for whole egg. The results were as follows: 1.In 39 determinations of endogenous urinary nitrogen it was found that in the majority of cases relatively constant values occurred during the last 5 days of a 14-day low-nitrogen feeding period. Shorter periods would have been unsatisfactory in most instances.2.The mean daily endogenous urinary nitrogen excretion was 1,454 ± 30.8 mg for determinations on 25 subjects. When these endogenous values were expressed in milligrams per kilogram of body weight, milligrams per square meter of surface area and milligrams per basal calorie, the average values were 25.2 ± 0.65, 898.0 ± 17.0 and 1.14 ± 0.021, respectively.3.The creatinine nitrogen constituted one-fourth of the total endogenous urinary nitrogen (actual mean value, 25.1% ± 0.40).4.The coefficient of variation of the mean value for the CN/EN ratio was 8.1%. For the endogenous nitrogen this coefficient was 10.6%, and it was 13.0, 9.5, and 9.4% for the endogenous data expressed per kilogram, per square meter, and per basal calorie, respectively.5.For each gram of dry matter consumed, the average metabolic fecal nitrogen was 0.88 ± 0.028 mg.6.When fed to 23 subjects, sunflower seed flour protein had a biological value of 61.2 ± 1.71 and was 89.9 ± 0.86% digestible. For 10 of these subjects, the protein of whole egg showed a biological value of 90.9 ± 2.23 and was 92.8 ± 1.39% digestible.7.Endogenous urinary nitrogen, estimated from the creatinine nitrogen × 3.984, together with estimated metabolic fecal nitrogen (obtained by multiplying 0.88 by the grams of dry matter consumed), was used in estimating the biological values of sunflower seed flour and of whole egg; resulting values were 61.6 ± 3.20 and 92.0 ± 2.35, respectively. For these subjects, expression of the endogenous nitrogen as a multiple of urinary creatinine reduced the variation between individual values more than when body weight, surface area or basal metabolism served as a basis of expression, as evidenced by the coefficients of variation for the mean values. The differences between the coefficients proved significant only in a comparison of the creatinine expression with that for body weight. On the basis of the data herein reporte