Skin tissue dielectric constant in women with high body fat content.

BACKGROUND: Skin tissue dielectric constant (TDC) measurements at a frequency of 300 MHz are used to assess skin properties in many conditions. Impacts of patient obesity on these values are unknown, and its quantitative assessment was the goal of this research.

MATERIALS AND METHODS: Women in a weight loss program (N = 32) had TDC measured on forearm, biceps, neck, jowl, and submental regions along with measurements of total body fat (TBF), water (TBW), intracellular water (ICW), and extracellular water (ECW) via multi-frequency bioimpedance. Group age (mean ± SD) was 40.0 ± 11.6 years (20-70 years) with body mass index (BMI) of 31.8 ± 6.7 Kg/m2 (23.0-49.9 Kg/m2 ). For analysis, subjects were divided into those with BMI < 30 Kg/m2 (subgroup A, n = 16) vs ≥30 Kg/m2 (subgroup B, n = 16).

RESULTS: Tissue dielectric constant at forearm and biceps decreased significantly (P < .001) with increasing depth from 0.5 to 1.5 to 2.5 mm but TDC values and their inter-side ratios did not differ between subgroups A and B at any measured site. Although correlations between TBW, ECW, and ICW were significant (P < .001), there was no dependence of TDC values on any of these parameters.

CONCLUSIONS: Previously unknown TDC values for obese persons are provided and based on subgroup analyses suggest that skin TDC values in overweight and obese persons are not confounded by variables such as TBW and TBF. Further, since inter-side ratios and their SD's yielded thresholds for forearm and biceps similar to those established for women with normal BMI, use of these clinical inter-arm TDC ratios now is extended to include a wider BMI range.