ENERGY EXPENDITURE AND BODY COMPOSITION IN PRADER-WILLI SYNDROME

Abstract

The assessment of energy expenditure (EE) in humans in a normal environment has recently become possible through measurement of the differential excretion of doubly labeled heavy water (2H218O) following oral ingestion. After 2H218O distribution, CO2 production and EE may be calculated from differential 2H and 18O enrichment in urine samples at 1 and 7 days. Further, isotope dilution at 4 hours may be used to calculate total body water and fat-free mass (FFM). We studied 10 individuals with Prader-Willi syndrome (PWS) (8-24 years) and 5 normal obese children (NO) (7-16 years). None had other chemical abnormalities, and both groups were similarly obese (PWS 157±9.7%, NO 152±11.7% ideal body weight). PWS were 47.9±2.3% fat comp. to NO 45.6±1.9% (N.S.). However, % fat linearly correlated with body mass index (kg/m2) only in PWS (r=0.93). Two normal-weight PWS had 40% and 37% body fat. EE in PWS was 2103±203 kcal vs. 3478±407 kcal, NO (p<.005). EE/kg FFM, 71.6±3.4 PWS vs. 76.3±6.4, NO, or EE/kg body weight, 37.6±2.6 PWS vs. 42.0±4.5, NO, was not significantly different, but the measured EE/calculated basal metabolic rate was less in the PWS, 1.34±.08 vs. 1.65±.12, NO, (p<.05). PWS have increased body fat even when of normal weight. EE in PWS normalized for FFM or weight is not significantly lower than in NO. These studies clarify the nature of obesity in PWS using a non-invasive technique with potential application to other disorders of EE and intake.