A standard calculation methodology for human doubly labeled water studies.

Area of Science:

• Human physiology
• Biomedical engineering
• Nutritional science

Background:

• The doubly labeled water (DLW) method is a gold standard for measuring total energy expenditure (TEE) in free-living individuals.
• Existing equations used to convert DLW isotopic data to TEE introduce significant variability.
• The accuracy of TEE estimation is sensitive to the dilution space ratio (DSR) of the isotopes used.

Purpose of the Study:

• To address the variability in TEE estimations caused by different equations in the DLW method.
• To propose a new, more accurate equation for calculating TEE, particularly for infants and children.
• To improve the reliability of energy expenditure measurements in diverse populations.

Main Methods:

• Analysis of the International Atomic Energy Agency (IAEA) DLW database, comprising 5,756 measurements from adults and children.
• Evaluation of the sensitivity of estimated carbon dioxide production (rCO2) to the dilution space ratio (DSR).
• Development and validation of a new equation based on an updated estimate of the mean DSR, incorporating non-linear body mass variations in infants (0-10 kg).

Main Results:

• Significant variability in TEE estimations was observed across different existing DLW equations.
• A new DSR-based equation was developed, showing improved agreement with indirect calorimetry for infants (average difference 0.64%; SD = 12.2%).
• The DSR was found to vary non-linearly with body mass in infants under 10 kg.

Conclusions:

• The proposed new equation, incorporating a body mass-dependent DSR for infants, enhances the accuracy of TEE measurements.
• Adoption of these refined equations is recommended for future DLW studies to improve data consistency and reliability.
• This work provides a more precise method for assessing energy expenditure, crucial for nutritional and clinical research.