Predictions of resting energy expenditure in amyotrophic lateral sclerosis are greatly impacted by reductions in fat free mass

Background: Hypermetabolism, defined as an increase in measured resting energy expenditure (mREE) relative to predicted REE (pREE), is recognised as an important feature of amyotrophic lateral sclerosis (ALS). Previous predictions of REE in ALS have not accounted for differences in fat free mass (FFM). This study aimed to investigate the effect of accounting for FFM on pREE in ALS patients and a matched control population. Methodology and findings: Body composition and pREE data were obtained from 50 ALS and 50 age- and sex-matched healthy control participants. We contrast conventional models for predicting REE that rely on anthropometric measures, age, and sex, with models that predict REE relative to FFM. Given that a significantly lower FFM was observed in ALS, models that consider FFM predicted significantly lower REE in ALS participants when compared to controls. Using Bland-Altman analysis, we demonstrate a prediction bias between models that do not account for FFM between the ALS and control populations. We also demonstrate greater agreement in predictions between control and ALS populations when correcting for FFM. Conclusions/significance: Future studies should correct for reductions in FFM when predicting REE in ALS.