Doubly Labelled Water

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Biochemical procedure that can estimate EE through biological markers that reflect the rate of metabolism in the body
Ingestion of a standardised amount of 2 stable isotopes of water 18O and 2H
The isotopes distribute themselves in equilibrium with the body water
Urine samples are collected at the beginning and end of the measurement period
Difference in elimination rates of the isotopes provide a measure of CO2 production and therefore EE
Pros
- Accurate and valid measurement of EE
- Applicable for children and adults
- Induces no change in PA behaviour
- Usual movement pattern
Cons
- Expensive: not for large-scale studies
- Requires expertise
- No indication of PA pattern, only EE