Rationale: About 50-60% of Amyotrophic Lateral Sclerosis (ALS) is characterized by an increase of metabolic rate. The increase of metabolic rate in ALS is defined by more than +10% of resting energy expenditure (REE) variation between measured REE (mREE) and calculated REE (cREE). However, the REE variation during ALS is a prognostic factor for the survival in patients with a REE variation over +20%. The present study aimed to study the relevant threshold of REE variation according to several cREE formulas to screen patients with the higher evolving risk. Methods: Nutritional assessments and body composition (by bioimpedance analysis) were performed in ALS patients. mREE was measured by IC and cREE was calculated using HB 1919 and 1984, World Schofield, De Lorenzo, Johnstone, Mifflin, WHO/FAO, Owen, Fleisch, Wang, Rosenbaum and Nelson formulas. Functional (Functional Rating Scale – Revised[ALSFRS-R] slope between diagnosis and last assessment) and Respiratory (Forced vital capacity [FVC] slope between diagnosis and last assessment) evolution and survival by Log-rank test (Hazard Ratio [HR], confidence interval [CI] 95%) according to two thresholds of REE variation 10% and 20% were studied. Results: 315 ALS patients with a median age at IC of 66.6 years (Interquartile range: 56.9–74.1) with a sex ratio of 1.0 were included. Depending on the predictive equation, REE variation over 10% and 20% was found in 35.2% to 76.3% and in 14.6% to 53.3% of ALS patients, respectively. Patients with REE variation over 10% with HB 1919 had a worst respiratory evolution (-3.2 %/month (-6.2 − -1.5), p = 0.03). Patients with REE variation over 20% with HB 1919 and HB 1984 had a lower survival (HR = 1.42 (1.10 − 1.99), p = 0.01; HR =1.38 (1.06 − 1.92), p = 0.02, respectively). Moreover, with this same threshold with Mifflin formula patients had a worst functional (-1.4 point/month (-2.2 − -0.6), p = 0.02) and respiratory (-3.5 %/month (-6.5 − -1.5), p = 0.03) evolution and a lower survival (HR = 1.42 (1.14 − 1.83), p = 0.003). Conclusion: In clinical practice REE formulas, such as HB 1919, HB 1984 or Mifflin, can be used as a reference value compared to IC to screen metabolic changes in ALS patients. With these formulas the threshold of REE variation of 20% seems the most interesting to screen at diagnosis ALS patients with a higher evolving risk.