Decline in Isotope Dilution Space Ratio Above Age 60 Could Affect Energy Estimates Using the Doubly Labeled Water...

Area of Science:

• Human physiology
• Metabolic research
• Biomarker validation

Background:

• Doubly labeled water (DLW) is the gold standard for measuring total energy expenditure (TEE).
• The accuracy of DLW measurements depends on the isotope dilution space ratio (DSR).
• Identifying factors influencing DSR can improve TEE measurement precision.

Purpose of the Study:

• To evaluate associations between DSR and various factors including age, sex, ethnicity, anthropometry, body composition, isotope turnover, and geographical elevation.
• To determine which factors significantly influence DSR in DLW measurements.

Main Methods:

• Utilized univariate regression and analysis of variance to explore relationships between variables and DSR.
• Employed general linear models (GLM) and 1-way ANOVA to assess simultaneous associations of age, sex, ethnicity, fat-free mass (FFM), and fat mass (FM) with DSR.
• Analyzed data from 5678 measurements across diverse global populations.

Main Results:

• The mean DSR was 1.0364 ± 0.0141, with no meaningful physiologic effect from most tested variables.
• DSR decreased with age in individuals aged 60 years and older (P < 0.001).
• In White adults younger than 60, DSR was not related to FFM or FM (P = 0.73) but was affected by age and sex (P < 0.001).

Conclusions:

• Age is a significant factor influencing DSR, particularly in older adults.
• Previous estimates of age-related decline in TEE may require revision.
• Further validation studies in older populations are recommended to confirm findings on DSR and TEE.