Energy expenditure and physical activity in Prader-Willi syndrome: comparison with obese subjects

Abstract

Prader-Willi syndrome (PWS) is a complex neurodevelopmental disorder characterized by hypotonia, suck and feeding difficulties, hypogonadism, small hands and feet, developmental delay, hyperphagia and early childhood obesity and a particular facial appearance. The obesity associated with PWS is the result of a chronic imbalance between energy intake and energy expenditure (EE) due to hyperphagia, decreased physical activity, reduced metabolic rate and an inability to vomit. EE is affected by body composition as well as exercise. Individuals with PWS have a lower lean body mass (LBM) compared with controls which may contribute to reduced basal level EE. To determine the relationship among body composition, activity levels and metabolic rates, dual energy X-ray absorptiometry (DEXA) and a whole-room respiration chamber were used to measure body composition, total EE (TEE), resting EE (REE), physical activity, and mechanical work (MW) during an 8 hr monitoring period. The chamber consisted of a live-in whole-room indirect calorimeter equipped with a force platform floor to allow simultaneous measurement of EE, physical activity, and work efficiency during spontaneous activities and standardized exercise. Participants with PWS (27 with 15q11-q13 deletion and 21 with maternal disomy 15 with an average age of 23 years) had significantly decreased TEE by 20% and reduced LBM compared to 24 obese subjects. Similarly, REE was significantly reduced by 16% in the individuals with PWS relative to the comparison subjects. Total MW performed during the 8 hr monitoring period was significantly reduced by 35% in the PWS group. The energy cost of physical activity is related to the duration, intensity and type of activity and the metabolic efficiency of the individual. After adjusting group differences in LBM by analysis of variance, TEE and REE were no longer different between the two groups. Our data indicate that there is a significant reduction of EE in individuals with PWS resulting from reduced activity but also from lower energy utilization due to reduced LBM which consists primarily of muscle.

FIG. 1

Schematic representation of a whole-room indirect calorimeter with an activity energy measurement system (AEMS) in place.

FIG. 2

Representative example of energy expenditure (EE), respiratory quotient (RQ), and mechanical work (MW) of an individual with Prader–Willi syndrome. Data collected using the activity energy measurement system (AEMS).

FIG. 3

Histogram showing resting energy expenditure (mean ± SD) for male and female subjects with Prader–Willi syndrome (PWS) or obesity. Resting energy expenditure is significantly different in PWS subjects compared to obese subjects (ANOVA; ^**P < 0.01, ^***P < 0.001).

FIG. 4

Scatterplots of (A) body mass index, (B) total lean mass, (C) and spontaneous physical activity energy expenditure correlated with resting energy expenditure in individuals with Prader–Willi syndrome (PWS) and obesity including Pearson correlation coefficients and significance.

FIG. 5

Scatterplots of (A) average energy expenditure, (B) average mechanical work, and (C) fat oxidation correlated with total lean mass in individuals with Prader–Willi syndrome (PWS) and obesity including Pearson correlation coefficients and significance.