AbstractObjective:To provide a framework for use of the doubly labelled water method to measure energy expenditure in order to validate dietary instruments for the assessment of energy.Design:Review and description of the use of doubly labelled water method for use as a biomarker for habitual energy intake.Results:The doubly labelled water method has a relative accuracy of 1% and within-subject precision of 5 to 8%. Comparison of self-reported energy intake with energy expenditure demonstrated that over one-third of individuals may underreport energy intake by more than 25%.Conclusions:The doubly labelled water method, although expensive and dependent on non-routine laboratory instrumentation, is an excellent biomarker of energy intake.