**2.3.1 Percentage of weight loss (% WL***)*

The percentage change of usual weight or percentage of weight loss (% WL) is determined using the patient's usual and current weights, as per the following equation:

$$\% \text{ WL} = \frac{\text{Usual Weight} - \text{Current Weight}}{\text{Usual Weight}} \times 100\%$$

The % WL highly reflects the extent of the disease. Patients with % WL values > 10% are classified as malnourished and above 10% severe malnutrition (Mahan; Escott-Stump, 2005).

### **2.4 Bioelectrical impedance analysis**

Bioelectrical impedance analysis (BIA) is a non-invasive technique that can be used to estimate body composition. The method uses low amperage current (single or multiple frequencies) that passes between two electrodes placed on the skin under the assumption that the current resistance (impedance) ranges on an inversely proportional basis to the fluid contained in the tissues and the content of electrolytes. BIA has a good correlation with body composition made with the isotope dilution, under controlled conditions (O'Brien; Young; Sawka, 2002).

In ALS, due to the limitations and difficulties during nutritional assessment, BIA has been a good tool in nutritional diagnosis. It is an easy, non-invasive technique, where fat-free and fat mass are obtained, in addition to the estimation of the degree of hydration. In 2003, the equation for BIA was validated in patients with ALS through cross-sectional and longitudinal studies, which was optimized at 50 kHz (Desport et al., 2003).
