1. The effect of an energy-restricted (46 kJ day−1 kg−1), adequate protein diet (1.47 g day−1 kg−1) on the nitrogen metabolism of five obese rapidly growing adolescents (two males and three females) was assessed by means of nitrogen-balance measurements and determination of whole-body nitrogen turnover.

2. The energy-restricted diet had no significant effect on nitrogen balance (P > 0.1) for the entire group when compared with the control dietary intake; however, significant (P < 0.01) differences in nitrogen balance were noted among individuals at each dietary interval.

3. Mean values for whole-body nitrogen turnover, protein synthesis and breakdown for the control period were: 45.5 ± 13.2 mg of nitrogen day−1 kg−1, and 5.72 ± 1.96 and 5.74 ± 1.92 g of protein day−1 kg−1 respectively. These values are 82% of those measured in infants.

4. Reducing the mean non-protein energy intake to 20 kJ day−1 kg−1 had no significant effect on whole-body nitrogen turnover, protein synthesis or protein breakdown.

5. The results are discussed in relation to the regulation of whole-body nitrogen metabolism, by dietary protein and energy intakes.

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