Differences In Body Water Compartment Ratios By Gender, Age, And Fat-free Mass

Abstract

INTRODUCTION: The extracellular water (ECW) compartment is used to signify disease states via edema or the expansion of interstitial water. The ratio of ECW to total body water (TBW) is an indication of normal fluid distributions. A ratio greater than 0.39 indicates malnutrition, aging, and obesity, while ratios less than 0.36 are seen in athletes or individuals with increased muscle mass. Additionally, the ratio of ECW to intracellular water (ICW) is used indicate fluid shifts in body water as it relates to increased adipose tissue. PURPOSE: To investigate the effects of gender, age, fat-free mass/weight (%FFM), BMI, and fitness level (FIT) on ECW/TBW and ECW/ICW ratios in healthy individuals. METHODS: Fifty healthy volunteers (36±15 yrs, 170.0±9.1 cm, 69.1±10.9 kg, 21 men, 29 women) followed standard pretest guidelines for body composition assessment. ECW (L) and ICW (L) were measured supine with a Xitron 4200 multifrequency BIA at the 5th minute according to Xitron recommendations. We investigated five independent variables (IV) (gender, age, BMI, FIT, and %FFM) and two dependent variables (DV) (ECW/TBW and ECW/ICW). Each IV was categorized into two groups by the median of the variable. Independent t-tests analyzed the differences of IV and DV (p<.05). RESULTS: Significant differences were found for gender, age, and %FFM. However, there were no significant differences based on BMI and FIT. Males displayed lower ECW/TBW (0.398±0.024) and ECW/ICW (0.664±0.068) compared to females (0.442±0.026 and 0.796±0.084, respectively). Younger participants (≤30.5 yrs) displayed lower ECW/TBW (0.412±0.033) and ECW/ICW (0.706±0.097) than older participants (>30.5 yrs) (0.436±0.030 and 0.776±0.094, respectively). Participants who had higher %FFM (>70.2%) displayed lower ECW/TBW (0.402±0.027) and ECW/ICW (0.677±0.077) than participants who had lower %FFM (≤70.2%) (0.445±0.024 and 0.805±0.080, respectively). CONCLUSION: Male gender, age ≤ 30.5 yrs, and %FFM >70.2% resulted in lower ECW/TBW and ECW/ICW ratios in our sample. Conversely, mean measurements of ECW/TBW were all seen to be higher than the upper limit for normal ECW/TBW (0.39) suggested for this population. This may suggest a need for re-evaluation of this limit. In our sample, BMI or FIT did not have significant differences in ECW/TBW or ECW/ICW ratios.