Energy expenditure and the accuracy of predictive equations in myotonic dystrophy type 1

BackgroundMyotonic dystrophy type 1 (DM1) is associated with reduced physical activity, overweight and cardiovascular morbidity. Nutritional management requires accurate estimation of total daily energy expenditure (TEE), based on basal metabolic rate (BMR) and physical activity level (PAL). However, DM1-related changes in body composition may reduce the accuracy of commonly used BMR equations. This study evaluated BMR equation accuracy in DM1 versus controls, and assessed PAL and substrate oxidation.MethodsIn this secondary analysis of a prospective case-control study, 15 DM1 patients were compared with 15 age-, sex-, and BMI-matched controls. Body composition was measured using dual-energy X-ray absorptiometry. Overnight metabolic rate (OMR) was assessed by room calorimetry and compared with standard predictive equations (Harris-Benedict, WHO, Mifflin-St Jeor). Additionally, OMR was compared to body composition-based equations (Wang, Nelson, Sabounchi structures 4, 5, and 11). TEE was measured over 15 days using doubly labeled water. PAL was calculated as TEE/OMR, and substrate oxidation was assessed using the respiratory exchange ratio (RER).ResultsStandard predictive equations significantly overestimated metabolic rate in DM1, with median biases of +100 to +165 kcal/day (+7% to +12%, p<0.01), with no significant bias in controls. Structure 11 performed best in DM1 (+0.0%, p=1.000). PAL was lower in DM1 than in controls (1.42 vs. 1.69, p<0.001), whereas RER did not differ.ConclusionCommon predictive equations overestimate energy requirements in DM1. Body composition-based approaches or correction factors may improve estimation, while low PAL should be considered when estimating TEE. These findings have direct implications for nutritional management in DM1.