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Endogenous nitrogen metabolism and plasma free amino acids in young adults given a ‘protein-free’ diet*

Published online by Cambridge University Press:  09 March 2007

V. R. Young  and
N. S. Scrimshaw
V. R. Young
Affiliation:
Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
N. S. Scrimshaw
Affiliation:
Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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Abstract

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1. Variation in endogenous nitrogen metabolism was determined by giving eleven healthy men, aged 17–22, a diet supplying daily only 6 mg N/kg body-weight. Eight subjects were given the diet for 7–10 days and three other subjects were given it for 16 days.

2. Body cell mass (BCM) was calculated from whole-body 40K in ten subjects and basal metabolism was determined in seven subjects during the ‘protein-free’ period. Urine was analysed daily for N and creatinine, and faecal N was measured in pooled samples. Plasma free amino acids, serum albumin and protein were measured in preprandial morning blood samples at the beginning and end of the study.

3. BCM did not change during the ‘protein-free’ period and accounted for 48% of the total body-weight. Basal calorie expenditure amounted to 48 ± 5 kcal/kg BCM per day.

4. Mean daily endogenous urinary N excretion in the eight subjects given the ‘protein-free’ diet for 7–10 days was 36·6 ± 3·0 mg N/kg body-weight, 79·4 ± 4·4 mg N/kg BCM and 1·6 ± 0·2 mg N/basal kcal. Endogenous faecal N excretion was 9·9 ± 1·1 mg N/kg body-weight and accounted for 20% of the total endogenous loss. Results obtained with three other subjects given the diet for 16 days were similar.

5. Plasma essential amino acids were reduced, glutamic acid, alanine and glycine increased, and the ratio of essential to non-essential amino acids decreased after 7 or 10 days of ‘protein-free’ diet.

6. The loss of endogenous N per basal kcal and of faecal N per kg body-weight was lower than the values assumed in the factorial approach to protein requirements by the FAO/WHO (1965) Expert Group on Protein Requirements.

Type
Research Article
Information
British Journal of Nutrition , Volume 22 , Issue 1 , February 1968 , pp. 9 - 20
Copyright
Copyright © The Nutrition Society 1968

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