Within-Individual Variability of Resting Metabolic Rate Over 12 Weeks

Resting metabolic rate (RMR) is a major component of total daily energy expenditure and is widely used in metabolic research. However, most studies rely on single or infrequent measurements, assuming RMR is stable within individuals.

Emerging evidence suggests that RMR exhibits measurable within-individual variability, but the temporal structure and magnitude of this variability remain poorly characterized.

This study will implement a high-frequency repeated-measures design, with RMR measured three times per week over 12 weeks using whole-room indirect calorimetry under standardized conditions. This approach will allow detailed characterization of short-term variability and provide estimates for within-subject variability, measurement error, and minimal detectable change.

The findings will inform interpretation of longitudinal metabolic studies and improve study design in future research.

• Repeated Measurement of Resting Metabolic Rate (Other): Repeated assessment of resting metabolic rate under standardized conditions; no intervention is administered.

Primary outcomes

• Within-Individual Variability in Resting Metabolic Rate (RMR) [12 weeks]: Within-individual variability in resting metabolic rate (RMR) assessed using repeated measurements under standardized conditions. Variability will be quantified using mean, standard deviation (SD), and coefficient of variation (CV%) across repeated measurements.

Secondary outcomes

• Minimal Detectable Change (MDC) in RMR [12 weeks]: The minimal detectable change in resting metabolic rate required to distinguish true physiological change from measurement variability.
• Between-Individual Variability in RMR [12 weeks]: Assessment of variability in resting metabolic rate between participants based on repeated measurements.
• Temporal Trends in RMR [12 weeks]: Assessment of systematic changes in resting metabolic rate over time using repeated measurements across the study period.

Sex: All, ages: 18 Years to 65 Years, accepts healthy volunteers

Inclusion Criteria:

* Adults aged 18-65 years
* Clinically healthy individuals
* Stable body weight (±2 kg) over the past 3 months
* Ability and willingness to attend morning measurements three times per week for 12 weeks
* Ability to provide informed consent

Exclusion Criteria:

* Known uncontrolled endocrine or metabolic disease
* Use of medications known to significantly affect resting metabolic rate (e.g., systemic corticosteroids, unstable thyroid hormone therapy)
* Acute illness within 14 days prior to enrollment
* Pregnancy or lactation
* Any medical condition that, in the opinion of the investigators, may interfere with safe participation

• Yftach Prof. Gepner, Principal investigator, Tel Aviv University