British Journal of Nutrition

Full Papers

Human and Clinical Nutrition

Age- and sex-standardised lean and fat indices derived from bioelectrical impedance analysis for ages 7–11 years: functional associations with cardio-respiratory fitness and grip strength

Andrea Sherriffa1 c1, Charlotte M. Wrighta1, John J. Reillya1, John McColla2, Andy Nessa3 and Pauline Emmetta4

a1 Division of Developmental Medicine, Faculty of Medicine, University of Glasgow, Glasgow G3 8SJ, UK

a2 Department of Statistics, University of Glasgow, Glasgow G12 8QQ, UK

a3 Department of Oral and Dental Science, University of Bristol, Bristol BS1 2LY, UK

a4 Department of Community Based Medicine, University of Bristol, Bristol BS8 2AA, UK


Indices for lean and fat mass adjusted for height derived from bioelectrical impedance for children aged 7 years have been published previously and their usefulness in the clinical assessment of undernutrition has been demonstrated. However, there is a need for norms that cover a wider age range and to explore their functional significance. The aim of the present study is to derive lean and fat indices for children aged 7–11 years and investigate associations with objective measures of cardio-respiratory fitness and grip strength. Subjects were 9574 children participating in the Avon Longitudinal Study of Parents and Children (ALSPAC). Bioelectrical impedance analysis (BIA) data collected longitudinally between ages 7 and 11 were used to derive lean and fat indices using the method of standardised residuals. Cardio-respiratory fitness (CRF) (9 years) and grip strength (11 years) were also measured. Correlation coefficients and 95 % CI were calculated to assess the strength of association between lean index, fat index and CRF and grip strength. Equations for calculating lean and fat indices in children aged 7–11 years relative to the ALSPAC population are presented. Lean index was linearly associated with CRF (rboys 0·20 (95 % CI 0·15, 0·25), rgirls 0·26 (95 % CI 0·22, 0·30)) and grip strength (rboys 0·29 (95 % CI 0·26, 0·32), rgirls 0·26 (95 % CI 0·23, 0·29)). BMI showed slightly weaker associations, while fat index was unrelated to either CRF or grip strength. Lean indices relate to muscle function and fitness while fat index does not.

(Received April 23 2008)

(Revised August 20 2008)

(Accepted September 16 2008)

(Online publication November 24 2008)


Abbreviations: ALSPAC, Avon Longitudinal Study of Parents and Children; BIA, bioelectrical impedance analysis; bpm, beats per min; CRF, cardio-respiratory fitness