Total energy expenditure assessed by doubly labeled water in patients with myotonic dystrophy type 1: Associations with body composition and functional status.

Background & AimsMyotonic dystrophy type 1 (DM1) is frequently associated with metabolic abnormalities and altered body composition, yet energy metabolism under free-living conditions remains incompletely characterized. This study aimed to characterize total energy expenditure (TEE) using the doubly labeled water (DLW) method and to examine its associations with body composition and functional status. Estimated energy balance was also explored as a secondary variable.MethodsTwelve patients with genetically confirmed DM1 were included. TEE was assessed using the DLW method. Body composition was evaluated using multifrequency bioelectrical impedance analysis. Energy intake was estimated from dietary records, and energy balance was calculated as energy intake minus TEE. Associations were examined using correlation analyses.ResultsThe mean TEE was 990 ± 169 kcal/day. TEE showed moderate positive associations with skeletal muscle mass and fat-free mass, and functional status was moderately associated with body weight-adjusted TEE. The mean energy intake was 1,355 ± 229 kcal/day, resulting in a positive energy balance of 366 ± 282 kcal/day; however, energy balance was not associated with body fat percentage or fat mass.ConclusionsDLW-measured free-living TEE was markedly low in DM1 patients with severe mobility limitation and reduced lean body mass despite largely normal BMI values. Estimated energy balance was not associated with adiposity. These findings suggest that functional severity and body composition should be considered when interpreting energy expenditure in DM1.