title: Energy expenditure by doubly labeled water: validation in lean and obese subjects.
abstract: The doubly labeled water (2H2(18)O) method to assess energy expenditure in free-living conditions has been successfully validated against gas exchange measurements in lean healthy volunteers in both sedentary conditions and during sustained heavy exercise. However, no data are available on obese subjects. We therefore compared the 2H2(18)O method with indirect calorimetry (respiratory chamber) in 12 male subjects covering a wide range of body weight and composition (61-190 kg, 7-41% fat). Isotope pool sizes and elimination rates were calculated from 18O and 2H enrichments in baseline urine samples and in 7-h, 11.5-h, and daily postdose urine samples using the multipoint slope/intercept method. Results were corrected for isotopic fractionation. Mean 7-day energy expenditure in the respiratory chamber varied from 1,851 to 4,105 kcal/day. The doubly labeled water method tended to underestimate energy expenditure (-2.5 +/- 5.8%, not equal to 0, range -14 to +4%), with the larger underestimate observed in heavier and fatter subjects (r = -0.82 and -0.68, P less than 0.02, respectively). The underestimation in heavier subjects might be related to larger sequestration of deuterium during fat synthesis. In conclusion, the doubly labeled water method is a suitable and accurate method to measure energy expenditure in free-living conditions but might provide a slightly underestimated figure in fatter subjects.
authors.affiliation: Clinical Diabetes and Nutrition Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Phoenix, Arizona 85016.
authors.forename: E
authors.initials: E
authors.lastname: Ravussin
authors.forename: I T
authors.initials: IT
authors.lastname: Harper
authors.forename: R
authors.initials: R
authors.lastname: Rising
authors.forename: C
authors.initials: C
authors.lastname: Bogardus
mesh_terms: D000273:Adipose Tissue / Q000502:physiology; D000328:Adult; D001130:Arizona; D015992:Body Mass Index; D001835:Body Weight; D002151:Calorimetry / Q000379:methods; D002245:Carbon Dioxide / Q000032:analysis; D003903:Deuterium; D002149:Energy Intake; D004734:Energy Metabolism; D006801:Humans; D007198:Indians, North American; D007553:Isotope Labeling / Q000379:methods; D008297:Male; D009765:Obesity / Q000378:metabolism*; D010103:Oxygen Isotopes; D012016:Reference Values; D044465:White People
chemical_list: D010103:Oxygen Isotopes; D002245:Carbon Dioxide; D003903:Deuterium