## 1 Introduction
In general, the average survival of patients with ALS is 3 to 5 years, but about 5% to 10% of patients live longer than 10 years [5; 7]. The ALS hallmark features encompass the gradual weakening of limb and respiratory muscles, with the common co-occurrence of dysarthria and dysphagia. In most cases, respiratory failure and malnutrition are the primary factors leading to mortality [1; 15; 16], typically occurring approximately 3 to 5 years after the onset of symptoms [17]. FFM provides less resistance. Additionally, body fluids and cell membranes contribute to conductivity and low impedance. In contrast, bone, fat, and triglycerides lack conductivity and have high impedance [22]. Many factors can influence the BIA results such as hydration status, ascites, edema, electrolyte balance, use of a pacemaker, body position, prior physical activity, body temperature, and dietary intake. Thus, an adequate standardization of BIA is required to achieve dependable measurements [18]. BIA can be complemented by the BIVA, developed by [PERSON] et al. [23]. In BIVA, R and Xc, adjusted for height, are represented as points on a graph. These points can be compared to tolerance ellipses set at 50%, 75%, and 95% based on a healthy population of the same gender and race. The size and shape of the ellipse change with age and body size [22]. This semi-quantitative method allows the determination of changes in body fluids, hydration status, and body cell mass [24]. The main advantage of BIA is that it can be used to evaluate patients directly using bioelectrical parameters, without relying on predictive equations or body weight [22]. BIVA tolerance ellipses interpretation stands that an abnormal situation is indicated when the experimental data falls outside the 95 th percentile ellipsis; a high body cell mass is suggested when the data are positioned above the long axis of the ellipsis; and hypohydration is inferred when the data appears to the right of the short axis of the ellipsis. The TBW shows an inverse relationship with the length of the impedance vector, and the combination of this vector's length and direction is referred to as the PhA [25]. BIVA has been used in the evaluation of BC and as a predictor of mortality in several neurological diseases, such as Duchenne muscular dystrophy (DMD) [26], Alzheimer's [27], Parkinson's [28], and systemic sclerosis [29]. BIVA may be an interesting approach to consider in ALS for a number of reasons. First, BIVA does not depend on error-prone predictive equations such as those used for BIA. Secondly, BIVA does not require weight, a parameter not always available, especially for patients in wheelchairs. Thirdly, BIVA is sensitive to identifying early and minimal changes in BC. Considering that nutritional status directly influences prognosis and survival in ALS, and that there is no gold standard method to assess the nutritional status, it is of the utmost importance to connect complementary data about nutritional status in ALS patients, especially those related to BC. We believe that taking PhA and BIVA into account, since the early stages of ALS, is critical in guiding nutrition interventions for maintaining proper nutritional status and avoiding malnutrition, factors that can improve the prognosis in ALS. We hypothesized that BIVA could bring new insights for nutrition evaluation and monitoring in ALS patients. Therefore, the aim of this study was to investigate the BC in ALS patients, including the BIVA approach, compared with matched healthy individuals.