Comprehensive Body Composition Measurement

Detailed physical measurements were made by trained personnel at all waves using identical procedures and instrumentation. Height was measured to the nearest 0.1 cm (Leicester Height Metre; Invicta Plastics, Leicester, UK) whilst barefoot, and weight was measured to the nearest 0.1 kg in light clothing (Tanita TBF-300 MA, Tanita, Tokyo, Japan) using standard procedures. BMI (kg/m²) was calculated and body tissue impedance (Ω) was measured by bio-impedance (Tanita TBF-300 MA). Subsequently, child-specific equations [17] (link) were used to derive multiple estimates of fat mass (FM, kg) and fat-free mass (FFM, kg) by utilising the data on height, weight, BMI, and body tissue impedance (values from equations predicting total body water were converted to FFM and FM using age- and sex-specific data on the hydration of lean tissue [18] (link)). All permutations were pooled alongside body composition measured by the Tanita TBF-300 MA to produce aggregated measures of FM and FFM [19] (link), which were expressed relative to height-squared (fat mass index (FMI), kg/m²) and height raised to the power of 2.5 (fat-free mass index (FFMI), kg/m^2.5), respectively [20] (link).