Total body protein in healthy adolescent girls: validation of estimates derived from simpler measures with neutron activation analysis.

ABSTRACT

BACKGROUND: Little recent and accurate information about body protein content in healthy adolescent girls is available. OBJECTIVE: The objective was to assess the total body nitrogen (TBN) and total body protein (TBPr) contents of fat-free mass (PFFM) in a group of healthy adolescent girls and to validate previously published TBN prediction equations. DESIGN: TBN was measured with in vivo neutron activation analysis (TBNNAA). Bone mineral density and FFM were measured with dual-energy X-ray absorptiometry (FFMDXA), total body water and FFM were measured with bioimpedance analysis, and FFM was assessed by measuring skinfold thicknesses in 51 girls with a mean (+/- SD) age of 14.7 +/- 0.7 y. The validity of the TBN prediction equations was assessed with Bland-Altman analysis. RESULTS: TBNNAA in our adolescent group was higher (1.49 kg) than values reported in earlier studies of women (1.25 and 1.31 kg), and PFFM was slightly higher (23%) than that documented in adults (19-21%). Previously published TBN equations showed either systematic bias or wide limits of agreement. CONCLUSION: A predictive equation derived from the present study population based on FFMDXA improves the prediction of TBN for groups of young girls but may not be helpful for individuals in clinical settings.