Accuracy of Smart Scales on Weight and Body Composition: Observational Study

Justine Frija-Masson, Jimmy Mullaert, Emmanuelle Vidal-Petiot, Nathalie Pons-Kerjean, Martin Flamant, Marie-Pia d'Ortho, Justine Frija-Masson, Jimmy Mullaert, Emmanuelle Vidal-Petiot, Nathalie Pons-Kerjean, Martin Flamant, Marie-Pia d'Ortho

Abstract

Background: Smart scales are increasingly used at home by patients to monitor their body weight and body composition, but scale accuracy has not often been documented.

Objective: The goal of the research was to determine the accuracy of 3 commercially available smart scales for weight and body composition compared with dual x-ray absorptiometry (DEXA) as the gold standard.

Methods: We designed a cross-sectional study in consecutive patients evaluated for DEXA in a physiology unit in a tertiary hospital in France. There were no exclusion criteria except patient declining to participate. Patients were weighed with one smart scale immediately after DEXA. Three scales were compared (scale 1: Body Partner [Téfal], scale 2: DietPack [Terraillon], and scale 3: Body Cardio [Nokia Withings]). We determined absolute error between the gold standard values obtained from DEXA and the smart scales for body mass, fat mass, and lean mass.

Results: The sample for analysis included 53, 52, and 48 patients for each of the 3 tested smart scales, respectively. The median absolute error for body weight was 0.3 kg (interquartile range [IQR] -0.1, 0.7), 0 kg (IQR -0.4, 0.3), and 0.25 kg (IQR -0.10, 0.52), respectively. For fat mass, absolute errors were -2.2 kg (IQR -5.8, 1.3), -4.4 kg (IQR -6.6, 0), and -3.7 kg (IQR -8.0, 0.28), respectively. For muscular mass, absolute errors were -2.2 kg (IQR -5.8, 1.3), -4.4 kg (IQR -6.6, 0), and -3.65 kg (IQR -8.03, 0.28), respectively. Factors associated with fat mass measurement error were weight for scales 1 and 2 (P=.03 and P<.001, respectively), BMI for scales 1 and 2 (P=.034 and P<.001, respectively), body fat for scale 1 (P<.001), and muscular and bone mass for scale 2 (P<.001 for both). Factors associated with muscular mass error were weight and BMI for scale 1 (P<.001 and P=.004, respectively), body fat for scales 1 and 2 (P<.001 for both), and muscular and bone mass for scale 2 (P<.001 and P=.002, respectively).

Conclusions: Smart scales are not accurate for body composition and should not replace DEXA in patient care.

Trial registration: ClinicalTrials.gov NCT03803098; https://ichgcp.net/clinical-trials-registry/NCT03803098.

Keywords: DEXA; obesity; smart scales.

Conflict of interest statement

Conflicts of Interest: JFM has received travel, accommodation, and meeting expenses unrelated to this work from Vitalaire, LVL Medical, Oxyvie, Ixxair Medical, and Boehringer-Ingelheim. No conflicts were declared for other authors.

©Justine Frija-Masson, Jimmy Mullaert, Emmanuelle Vidal-Petiot, Nathalie Pons-Kerjean, Martin Flamant, Marie-Pia d'Ortho. Originally published in JMIR mHealth and uHealth (https://mhealth.jmir.org), 30.04.2021.

Figures

Figure 1
Figure 1
Bland-Altman plots of the three scales for body weight, fat mass, and muscular mass. The red line indicates mean error, blue lines indicate 2.5 and 97.5 percentiles of the error distribution, and the black line represents a linear fit.

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