Korean J Fam Pract 2019; 9(1): 114-117  https://doi.org/10.21215/kjfp.2019.9.1.114
Evaluation of Appropriacy of Taking Water 2 Hour before Bioelectrical Impedance Analysis: Single- Frequency Bioelectrical Impedance Analysis Versus Multi-Frequency Bioelectrical Impedance Analysis
Ji-Hyun Kim, Boo-Yoon Cheung, Yong-Joo Lee, Whan-Seok Choi*
Department of Family Medicine, College of Medicine, The Catholic University of Korea, Seoul, Korea
Whan-Seok Choi, Tel: +82-2-2258-2894, Fax: +82-2-2258-2907, E-mail: fmchs@catholic.ac.kr, ORCID: http://orcid.org/0000-0001-8978-9885
Received: August 23, 2017; Revised: September 6, 2017; Accepted: September 18, 2017; Published online: February 20, 2019.
© The Korean Academy of Family Medicine. All rights reserved.

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background: Bioelectrical impedance analysis (BIA) can be used to estimate body composition. To achieve the best results, the manufacturer’s guidelines advise that individuals should restrict intake of food or caffeine, avoid vigorous exercise for 4 hours, and drink 2–4 glasses of water 2 hours before testing. We evaluated the appropriacy of drinking 2–4 glasses of water 2 hours before the BIA, as the validity of this indication has not been specifically demonstrated, by comparing intracellular water (ICW), extracellular water (ECW), total body water (TBW) in the fasting state, and after 1 and 2 hours of ingesting 500 mL of water.
Methods: Twenty-nine healthy adult men (n=10) and women (n=19) were recruited for the study. In the fasting state, the InBody 720 analyzer was used as multi-frequency (MF)-BIA and the output was recorded to determine the exact weight. Subsequently, Medinex BIA 450 analyzer was used as single-frequency (SF)-BIA, and the output was recorded. After drinking 500 mL of water 1 or 2 hours before assessment, the BIA tests were repeated as indicated above, and the ICW, ECW, TBW were compared by repeated measures ANOVA.
Results: SF-BIA measurements showed that compared to fasting state, the ICW decreased by approximately 0.56 L after 1 hour of drinking (P=0.001). The ECW was increased by about 0.62 L, 1 hour after drinking water compared to the fasting state (P=0.002). There were no significant differences between the results of BIA testing at 1 and 2 hours of fluid intake. The MF-BIA measurements indicated that testing after fasting, or 1 or 2 hours after fluid intake, did not result in significantly different ICW and ECW values. TBW showed no significant differences in the fasting state, or after 1 or 2 hours of fluid intake for both SF and MF.
Conclusion: Several studies have shown that bioelectrical impedance should be measured in the fasting state. But not the food intake, drinking 500 mL of water may be permitted when measuring MF-BIA. However, for SF-BIA measurements, fluid intake resulted in an increase in the ECW level and a decrease in ICW.
Keywords: Single-Frequency Bioelectrical Impedance Analysis; Multiple-Frequency Bioelectrical Impedance Analysis; Intracellular Water; Extracellular Water; Total Body Water
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