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Nitrogen Retention, Total Body ⁴⁰K and Weight Gain in Teenage Pregnant Girls^1,2,

Department of Nutritional Sciences, University of California, Berkeley, California 94720

Nitrogen (N) retention was measured in 10 primigravid women, 15 to 19 years of age, during the third trimester, by balance technique. The subjects were fed nutritionally adequate, natural food diets for several 12-day periods. Urinary creatinine excretion was used as a parameter of lean body mass in order to relate N intake to lean body size. Total N intake ranged from 9.3 to 20.0 g per day, with 90% from animal sources. Nitrogen balance was positive over all levels studied, varied from 0.31 to 6.50 g per day, and correlated highly with N intake. Nitrogen retention values were documented by appropriate weight gain and potassium (K) deposition. As measured by total body ⁴⁰K counts, K accretion was 3.4 mEq per day, which would represent 1.6 g N deposition at the K:N ratio of fetal tissue (2.15:1). The average observed N retention was 2.4 g per day. The slope of the regression line relating N intake to retention indicated a low efficiency of N utilization, 30%; but predicted the same endogenous output, 1.73 g per day, in this group of pregnant adolescents as has been previously reported for nonpregnant college women.

KEY WORDS: • nitrogen balance • pregnancy • adolescents • protein requirements • nitrogen utilization • total body ⁴⁰K • weight gain

¹ Supported in part by National Institutes of Health Grant HD 05246-02. USPHS Grant AM 10202-6 and USPHS Training Grant GM 1188-08.

² Taken from a thesis submitted by Janet C. King in partial fulfillment of the requirements for the Ph.D. degree, University of California, Berkeley, March, 1972.

Manuscript received 16 November 1972.

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