Day-to-day variability in euvolemic body mass

Area of Science:

• Physiology
• Nephrology

Background:

• Short-term body mass variability is common but understudied.
• Physiological body mass variability is minimal in healthy individuals but significant in patients with impaired volume homeostasis, such as those with kidney failure undergoing renal replacement therapy.

Purpose of the Study:

• To quantify short-term body mass variability in a healthy individual over a long period.
• To assess the implications of body mass variability for weight-dependent medical treatments.

Main Methods:

• Analysis of a long-term dataset (9521 days) of standardized body mass measurements from one healthy male.
• Calculation of relative differences in body mass between subsequent days to assess variability.

Main Results:

• The standard deviation of daily body mass relative difference was 0.53%, increasing to 0.69% for a 7-day interval.
• Body mass variability remained constant throughout the observation period.
• A 7-day body mass variability of approximately 0.6% (±450 mL for a 75 kg individual) was observed.

Conclusions:

• Body mass variability of around 0.6% should be considered in weight-dependent treatment prescriptions, such as ultrafiltration rates in hemodialysis.
• Implementing a "soft target weight" that accounts for longitudinal variations in body mass may enhance treatment quality for patients with volume regulation issues.