Precision of the doubly labelled water method using the two-point calculation.

Area of Science:

• Human Physiology
• Biotechnology
• Metabolic Research

Background:

• The doubly labeled water (DLW) method is a gold standard for measuring human energy expenditure.
• Accurate measurement of metabolic rate is crucial for understanding human physiology and health.
• Previous models of DLW precision assumed analytical error was the primary limiting factor.

Purpose of the Study:

• To investigate the intrasubject precision of the doubly labeled water method.
• To determine how metabolic period length and initial isotope enrichment affect DLW precision.
• To identify factors limiting the accuracy of the DLW method.

Main Methods:

• Analysis of intrasubject precision in seven subjects with single isotope doses and three with multiple doses.
• Varying the length of the metabolic period and initial isotope enrichment.
• Comparison of observed precision with predictions from a previously published model.

Main Results:

• Intrasubject precision was 5-6% for metabolic periods up to 14 days.
• Precision decreased with longer metabolic periods and lower initial isotope enrichment.
• Observed loss of precision was 2-10 times greater than predicted by the model.
• The intercept method for determining isotope dilution spaces did not improve precision.

Conclusions:

• The accuracy of the doubly labeled water method is sensitive to metabolic period length and initial isotope enrichment.
• Unmeasured changes in natural isotopic abundances from diet may limit model predictions.
• Optimal DLW use requires an initial isotope enrichment 500-600 times analytical error and a metabolic period of 1-3 biological half-lives.