We tested the validity and reliability of the BioSpace InBody 320, Omron and Bod-eComm body composition devices in men and women (n 254; 21 -80 years) and boys and girls (n 117; 10-17 years). We analysed percentage body fat (%BF) and compared the results with dual-energy X-ray absorptiometry (DEXA) in adults and compared the results of the InBody with underwater weighing (UW) in children. All body composition devices were correlated (r 0·54 -0·97; P#0·010) to DEXA except the Bod-eComm in women aged 71-80 years (r 0·54; P¼ 0·106). In girls, the InBody %BF was correlated with UW (r 0·79; P#0·010); however, a more moderate correlation (r 0·69; P# 0·010) existed in boys. Bland -Altman plots indicated that all body composition devices underestimated %BF in adults (1·0 -4·8 %) and overestimated %BF in children (0·3 -2·3 %). Lastly, independent t tests revealed that the mean %BF assessed by the Bod-eComm in women (aged 51-60 and 71-80 years) and in the Omron (age 18-35 years) were significantly different compared with DEXA (P#0·010). In men, the Omron (aged 18 -35 years), and the InBody (aged 36-50 years) were significantly different compared with DEXA (P¼0·025; P¼ 0·040 respectively). In addition, independent t tests indicated that the InBody mean %BF in girls aged 10 -17 years was significantly different from UW (P¼ 0·001). Pearson's correlation analyses demonstrated that the Bod-eComm (men and women) and Omron (women) had significant mean differences compared with the reference criterion; therefore, the %BF output from these two devices should be interpreted with caution. The repeatability of each body composition device was supported by small CV (, 3·0 %).Body fat: Bioelectrical impedance: Dual-energy X-ray absorptiometry: Underwater weighing Childhood and adult obesity is an epidemic in the USA (1 -3) and it is important to have valid and reliable tools to assess growth and body composition. It is essential that we develop safe and accurate tools to assess body composition as well as devices that are affordable. Devices that accurately depict body fat percentage (%BF) can be used as a tool to evaluate an individual's weight loss or gain over a period of time. Body composition analysis is important for understanding proportional changes in fat and lean mass for healthy individuals as well as individuals with various health conditions. Over the past several years there has been an increase in the marketing and sales of economical body composition analysers (i.e. bioelectrical impedance devices). Therefore, a greater need has developed to evaluate the accuracy of these body composition devices. In addition, practical indicators of %BF for different age ranges and sex are needed for epidemiological and clinical studies.Traditionally, assessing body composition relied upon the principle of underwater weighing, regarded as the 'gold standard' (4) ; however, technology has improved and various devices have been introduced to evaluate body composition. Dual-energy X-ray absorptiometry (DEXA) has become the preferred met...

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