Identification of Dampness Constitution Based on Bioimpedance Analysis: Independent Associations Between Extracellular Fluid and Trunk Reactance

Summary

This cross-sectional study identifies extracellular water and trunk reactance, measured via bioelectrical impedance analysis, as independently associated with the dampness constitution. These quantifiable parameters suggest differences in body fluid status and trunk bioelectrical properties.

Abstract

This study aimed to identify objective bioelectrical impedance analysis (BIA) parameters independently associated with the dampness constitution (phlegm-dampness and damp-heat constitutions) in Traditional Chinese Medicine (TCM), thereby providing candidate indicators for its objective identification. In this cross-sectional study, 232 participants (129 with the Harmonious constitution and 103 with the dampness constitution) were consecutively recruited from a community-based health screening program. Whole-body and segmental fluid distribution, bioelectrical parameters, and grip strength were measured. Core features were identified using Least Absolute Shrinkage and Selection Operator (LASSO) regression, and their independent associations with the dampness constitution were assessed using multivariable logistic regression; sex-stratified and sensitivity analyses (Winsorization and additional adjustment for waist-to-hip ratio or abdominal circumference) were also performed. LASSO identified five core features: left lower limb phase angle (PA_LL), trunk reactance (Reactance_TR), extracellular water (ECW), body fat percentage (PBF), and mean grip strength. In the multivariable model, ECW (OR = 1.307, 95% CI: 1.046–1.649, p = 0.021) and Reactance_TR (OR = 2.163, 95% CI: 1.124–4.267, p = 0.023) were independently and positively associated with the dampness constitution. In sex-stratified analyses, both associations were statistically significant in men (ECW: OR = 1.407, p = 0.038; Reactance_TR: OR = 2.764, p = 0.030) but not in women. Formal interaction testing did not support a statistically significant sex difference (sex × ECW: p = 0.573; sex × Reactance_TR: p = 0.605), suggesting that the apparent sex difference may reflect lower statistical power in the smaller female subgroup. The associations remained stable in all sensitivity analyses. In conclusion, ECW and Reactance_TR are two core BIA indices independently associated with the dampness constitution, suggesting trunk fluid retention and altered bioelectrical properties in affected individuals. These parameters constitute preliminary candidate indicators for the objective identification of the dampness constitution and require validation in independent populations.

Introduction

According to the theory of constitutional medicine in Traditional Chinese Medicine, an individual’s constitution constitutes the internal context for the onset, progression, and outcome of disease¹. Among these, dampness constitutions (phlegm-damp and damp-heat constitutions) are common types of constitutional imbalance encountered in clinical practice² and are significantly associated with an increased risk of adverse health outcomes such as metabolic disorders, frailty, and cardiovascular and metabolic diseases^3,4. However, the current assessment of dampness constitutions primarily relies on questionnaire evaluations or the clinical judgment of TCM practitioners⁵, while the ability of BIA parameters to accurately determine an individual’s constitution remains to be verified.

BIA may provide potential indicators for effectively identifying body composition types. Previous studies have shown that body fluid distribution parameters derived from BIA, together with cell membrane function parameters, can go beyond traditional measures of muscle mass to more sensitively reflect the body’s functional status and long-term prognosis. For example, a BIA-derived extracellular water to intracellular water ratio (ECW/ICW) has been shown to be independently associated with all-cause mortality and adverse clinical outcomes^6,7. An elevated extracellular water to total body water ratio (ECW/TBW) is also closely associated with lower limb functional decline and reduced muscle strength⁸. Furthermore, phase angle (PhA) and reactance (Xc), as markers of cell membrane integrity and body cell mass, offer unique advantages in monitoring early functional decline, malnutrition, and inflammatory states^8,9,10. Of particular note is that local body fluid parameters can predict functional performance in specific regions more accurately than systemic indicators^11,12, and that the direct use of raw parameters such as Xc may reflect changes in muscle function more directly than muscle mass estimated via equations¹³. These studies provide a solid theoretical basis for developing BIA-based methods to assess the dampness constitution.

Regarding constitutional typing, previous studies have attempted to correlate BIA parameters with TCM constitutions. Serum proteomics analysis has revealed differential expression of immune- and inflammation-related proteins in individuals with the dampness constitution². Furthermore, the BIA-derived ECW/TBW ratio measured by BIA has been shown to be closely associated with functional decline and volume overload¹⁴, and an increase in BIA-derived extracellular water may be accompanied by elevated levels of inflammation¹⁵. Abnormalities in fluid metabolism and inflammatory states constitute key pathological mechanisms underlying the ‘viscous and turbid’ characteristics of the dampness constitution. However, studies have not systematically evaluated multidimensional BIA parameters specifically in relation to the dampness constitution, and the potential value of segmental raw electrical parameters remains largely unexplored. Therefore, investigating the independent association between multidimensional BIA parameters and the dampness constitution is expected to provide a new dimension for the objective identification of this constitution.

In summary, this study utilized a LASSO regression system to identify core BIA indicators independently associated with the dampness constitution and assessed the independent contribution of these selected indicators via multivariate logistic regression. Furthermore, sensitivity analyses were performed to explore potential differences in the associations between sexes. This provides a theoretical basis and candidate indicators for developing BIA-based measures that effectively identify the dampness constitution.

Protocol

This study was reviewed and approved by the Ethics Committee of the Shanghai Pudong New Area Beicai Community Health Service Center (approval no. 20250425AR; approved April 25, 2025). All participants provided written informed consent prior to inclusion.

Research design and study population

This cross-sectional study aimed to identify objective indicators associated with the dampness constitutions (Phlegm-Dampness and Damp-Heat) using BIA. Participants were recruited from a community-based health screening program conducted at the Beicai Community Health Service Center (Pudong New Area, Shanghai) between July 1, 2025, and January 5, 2026. All individuals who completed both the TCM constitution assessment and the BIA measurement during this period were enrolled consecutively. Participants with missing data on any key variable were excluded. A total of 232 participants were ultimately included, comprising 129 in the Harmonious constitution group and 103 in the dampness constitution group.

Diagnostic criteria for dampness constitution

Constitution assessment was carried out using a patented portable smart mirror for traditional Chinese medicine (TCM) constitution analysis (Hi-Face22; Chinese utility model patent No. ZL 2021 2 1286496.5), which applies the standardized nine-constitution classification framework of TCM and generates a quantified constitution diagnosis from facial features and built-in questionnaire responses. Participants identified as having the phlegm-damp or damp-heat constitution as the predominant type were included in the dampness constitution group; those meeting the criteria for the harmonious constitution and showing no other constitutional imbalance were included in the control group². To our knowledge, peer-reviewed validation of this device against an independent reference standard (e.g., expert TCM assessment or a validated questionnaire) has not been published; this is acknowledged as a limitation.

BIA and body composition measurement

BIA measurements were performed using a multifrequency, eight-point tactile electrode segmental bioelectrical impedance analyzer (InBody 770, see Table of Materials), in strict accordance with the manufacturer's standard operating procedures. The device applies alternating currents at multiple frequencies (1, 5, 50, 250, 500, and 1,000 kHz) and is phase-sensitive, directly measuring resistance (R), reactance (Xc), and phase angle (PhA) for the whole body and five segments (right arm, left arm, trunk, right leg, left leg) via tetrapolar electrode configurations. Trunk resistance, reactance, and phase angle were measured between the right hand and right foot electrodes and recorded at 50 kHz. It should be noted that BIA devices directly measure bioelectrical parameters that are affected by body fluid and electrolyte status; the reported fluid volumes and body composition values are estimates derived from the device's prediction equations. Prior to measurement, subjects were required to fast for at least 2 h, avoid strenuous exercise for 12 h, and empty their bladders. During measurement, subjects stood barefoot on the foot electrodes and held the hand electrodes with both hands. The following body composition parameters were recorded: Total Body Water (TBW), Intracellular Water (ICW), Extracellular Water (ECW), ECW/TBW ratio (numerical value and percentage), TBW/Fat-Free Mass (TBW/FFM) ratio, Percentage of Body Fat (PBF), Body Fat Mass (BFM), Visceral Fat Area (VFA), Fat Mass Index (FMI), Obesity level, Skeletal muscle mass (SMM), Lean body mass (SLM), Fat-free mass (FFM), Body cell mass (BCM), Protein, Upper arm circumference (AMC), Basal metabolic rate (BMR). The following segmental bioelectrical parameters were recorded: Whole-body phase angle (PA_Whole), right upper limb phase angle (PA_RA), left upper limb phase angle (PA_LA), trunk phase angle (PA_TR), right lower limb phase angle (PA_RL), left lower limb phase angle (PA_LL), trunk impedance (Impedance_TR), trunk reactance (Reactance_TR). Simultaneously, the following anthropometric parameters were measured: height, weight, Body Mass Index (BMI), waist-to-hip ratio (WHR), abdominal circumference, and left and right calf circumferences.

Grip strength measurement

Grip strength was measured with a digital handgrip dynamometer (see Table of Materials). After two maximum isometric contractions on each hand, alternating between the left and right hands with a one-minute rest between contractions, the mean of the two trials of the dominant hand was calculated and used for analysis (Mean_Grip)

Statistical analysis

The overall analytical framework LASSO-based feature screening followed by multivariable logistic regression, with sex-stratified and sensitivity analyses) was defined a priori. However, the specific features entering the final model were determined by data-driven LASSO selection, and the sex-stratified and sensitivity analyses should be regarded as exploratory. No missing values were present for any of the variables included in the analysis. Continuous variables that followed a normal distribution were expressed as mean ± standard deviation; those that did not follow a normal distribution were expressed as median (interquartile range); categorical variables were expressed as frequency (percentage). Comparisons between groups were performed using the independent samples t-test, the Mann-Whitney U test, or the chi-squared test, with P < 0.05 considered statistically significant.

Subsequently, BIA features were screened using LASSO regression; the optimal penalty parameter λ was determined via 10-fold cross-validation, and features with non-zero coefficients at the λ that minimized the cross-validation error (λ.min) were selected. The model's discriminatory power was assessed using the area under the receiver operating characteristic curve (AUC). The 10-fold cross-validation procedure was used solely to select the LASSO penalty parameter λ and did not serve as validation of the final model; internal validation of the final model was performed using bootstrap optimism correction (1,000 resamples) and 5-fold cross-validation, and multicollinearity was assessed using the variance inflation factor (VIF), with values below five considered acceptable. Model calibration was assessed using the Hosmer–Lemeshow goodness-of-fit test and the bootstrap-corrected calibration slope. The clinical net benefit was evaluated using decision curve analysis (DCA). DCA was performed over the full threshold probability range of 0–1.0, with net benefit expressed relative to the 'treat all' and 'treat none' reference strategies. The clinical decision scenario was whether to recommend further assessment or intervention for the dampness constitution among community screening participants.

Subsequently, the features identified via LASSO screening, along with age and sex, were incorporated into a multivariable logistic regression model to assess the independent association of each indicator with the dampness constitution, yielding odds ratios (ORs) and 95% confidence intervals (CIs).

Subgroup analyses were conducted by sex to assess the stability of the associations. Sensitivity analyses included: (1) applying 1% and 99% Winsorization to continuous variables; and (2) additional adjustment for waist-to-hip ratio or abdominal circumference. All statistical analyses were performed using R version 4.5.2.

Results

Baseline characteristics

This study included 232 participants, comprising 129 (55.6%) in the Harmonious constitution group and 103 (44.4%) in the dampness constitution group (Table 1). There were no statistically significant differences between the two groups in terms of age, sex, or grip strength (P > 0.05). However, significant differences were observed between the dampness constitution group and the Harmonious constitution group in body composit...

Discussion

This study investigated the potential identification of the dampness constitution in Traditional Chinese Medicine using BIA parameters. Through systematic screening and correlation analysis, ECW and Reactance_TR were identified as core indicators independently associated with the dampness constitution. These associations remained stable across all sensitivity analyses. In sex-stratified analyses, they were statistically significant in men but not in women, and formal interaction testing did not support a statistically si...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Digital grip strength meter	ANTA	EH101	N/A
Hi-Face22 smart mirror	Beijing Xima Medical Technology Co., Ltd.	ZL202121286496.5	N/A
InBody 770 body composition analyzer	InBody Co., Ltd.	770	N/A
R statistical software (version 4.5.2)	R Foundation for Statistical Computing	https://www.r-project.org/	RRID:SCR_001905