A COMPARATIVE-STUDY OF DIFFERENT MEANS OF ASSESSING LONG-TERM ENERGY-EXPENDITURE IN HUMANS

We compared three independent techniques for measurement of total ener gy expenditure (TEE) in human subjects: 1) weight-maintaining energy i ntake (dietTEE), 2) 24-h chamber calorimetry (chamberTEE), and 3) diff erential elimination rates (H2O)-H-2 and (H2O)-O-18 (isotopeTEE). Twen ty-three healthy adult in-patients [19 never obese (NO), 2 obese (OB), and 2 formerly-obese (RO); 9 female, 14 male] ingested a liquid formu la diet (40% of calories as fat, 45% carbohydrate, 15% protein), the v olume of which was adjusted until body weight was stable for at least 14 days. Body composition was then determined by hydrodensitometry, is otope dilution, and dual photon beam absorptiometry (DXA). The thermic effect of feeding (TEF) and resting energy expenditure [REE; measured before arising (dietREE) and after arising (chamberREE)] were determi ned by indirect calorimetry. Non-resting energy expenditure (NREE) was calculated as NREE = TEE - (REE + TEF). Subjects then gained or lost 10% of their body weight and were restudied as described above. All me asures of TEE were significantly correlated (dietTEE vs. chamberTEE r( 2) = 0.75; dietTEE vs. isotopeTEE r(2) = 0.88; isotopeTEE vs. chamberT EE r(2) = 0.73; P < 0.0001). ChamberTEE (mean +/- SE = 2,107 +/- 64 kc al/day) was similar to 20% lower than either dietTEE (2,536 +/- 94 kca l/day, P < 0.0001) or isotopeTEE (2,564 +/- 83 kcal/day, P < 0.0001). When data were normalized to metabolic mass, weight gain of 10% was as sociated with significant increases in dietTEE (P < 0.005) and isotope TEE (P < 0.05) but not chamberTEE; weight loss of 10% was associated w ith significant reductions in dietTEE (P < 0.005) and isotopeTEE (P < 0.05) but not chamberTEE. We conclude that measures of energy expendit ure obtained in a highly controlled environment by caloric titration ( dietTEE) or differential excretion rates of (H2O)-H-2 and (H2O)-O-18 ( isotopeTEE) are not significantly different and that measurements of T EE obtained in a respiratory chamber (chamberTEE) are significantly lo wer than dietTEE or isotopeTEE, probably largely due to limitations on physical activity in the chamber.