## 4 Discussion  
In this study, we evaluated BC and bioelectrical parameters in Brazilian ALS patients compared to healthy peers. Our main results showed that ALS patients presented low levels of BMI, FFM, R/H, Xc/H, hydration, and cellularity, compared to the control group. Malnutrition is frequent in ALS patients [2; 17], affecting 9 to 55% of them [41]. Authors have shown that patients with a weight loss of 5% or more at the time of diagnosis experience a twofold increase in the risk of death [42]. Also, weight loss is associated with a poor prognosis in different periods of the disease, even before its onset [1; 15; 18; 33; 43]. Overweight or additional feeding to maintain BMI is advantageous and prolongs survival in ALS [1]. A high BMI can positively influence the survival of ALS patients [44]. The main causes of malnutrition in ALS include dysphagia, poor oral intake, progressive muscle degeneration, and potential hypermetabolism. Therefore, it is crucial to conduct nutrition evaluations and regularly monitor these patients [2]. In individuals with ALS, the catabolism (breakdown of FM and FFM) is well documented, and it is usually a consequence of reduced food consumption, increased metabolic rate, and denervation of skeletal muscle [41; 42; 45; 46]. Hypermetabolism in ALS is contradictory, and its origin remains unknown. Theoretically, catabolism, especially marked by muscle atrophy in ALS patients, should be followed by a decreased metabolic rate since the muscle is the most metabolically active tissue in the body [47]. However, the common hypermetabolism in ALS patients might occur as a consequence of a set of factors,  
Figure 2: Confidence ellipses of ALS patients (cases) (in red) and healthy subjects (controls) (in blue). The statistical analysis was performed by [PERSON]’s T2 test. R/H, Resistance/Height. Xc/H, Reactance/Height. including denervation of skeletal muscle, mitochondrial dysfunction, increased respiratory muscle expenditure, and hypothalamic atrophy [48; 49]. Muscle denervation can elevate the oxygen utilization rate, mitochondrial dysfunction impairs oxygen use and energy production, heightened respiratory effort adds more energy demand and hypothalamic atrophy can influence food intake and energy expenditure, changing neuroendocrine mechanisms related to the overall metabolism [48]. Studies have confirmed that hypermetabolism [50; 51; 52; 53; 54; 55] affects not only body composition but the prognosis, especially in those ALS patients with low BMI at the time of diagnosis [56]. Also, hypermetabolism is an independent risk factor for death and tracheostomy in ALS [55]. In our study, we identified significantly lower BMI and FFM values in ALS patients when compared to healthy controls. In addition, no difference was found in FM between the groups. Interestingly, [PERSON] et al. (2022) observed no significant difference in BC between ALS patients and controls, except BMI [15]. On the other hand, [PERSON] et al. (2011) identified significantly lower BMI and FFM values in ALS patients, comparing at diagnosis and before death [42]. Although BMI is a common indicator for evaluating the nutritional status of people and is even recommended by guidelines for the nutritional assessment of patients with ALS [5; 11], this parameter does not differentiate between body composition compartments, such as FM and FFM. Thus, an exploration of BC, rather than solely relying on BMI, could be beneficial in guiding nutritional interventions, as well as in evaluating disease progression and survival. Investigating BC and prognosis in ALS patients, a study has revealed that men experience more pronounced deterioration in their BC than women, leading to a swifter disease progression and reduced lifespan. This accelerated decline may be explained by men having less FM and more metabolically active FFM, resulting in lower energy storage [1]. Loss of FFM can also be considered a risk factor, accelerating progression, and causing early death [57].