Because of the inefficacy of standard methods for the evaluation of body composition of grade III obese individuals, it is difficult to analyze the quality of weight loss after bariatric surgery in these patients. Electrical bioimpedance vector analysis and the RXc graph uses crude resistance (R) and reactance (Xc) values, like components of the Z vector, to monitor variations in body fluid and the nutritional status of obese individuals. Using bioelectrical impedance vector analysis (BIVA) and the RXc graph, the objective of the present study was to evaluate long-term changes in weight and body composition of obese women after Roux-en-Y bariatric surgery. A study was conducted on 43 grade III obese women submitted to bariatric surgery. Anthropometric and bioimpedance (800 mA-50 kHz) data were obtained during the preoperative period and 1, 2, 3, and 4 y after surgery. BIVA was performed by plotting resistance and reactance values corrected for body height (R/H and Xc/H, Ohm/m) as bivariates on the RXc graph. BIVA software was used to plot the vectors of the RXc plane. Surgery promoted changes in body composition, with a reduction of fat mass and of fat-free mass. During the postoperative period, the vectors demonstrated migration to the right lower quadrant of the graph, corresponding to the classification of cachexia and water retention. Weight loss due to surgery results in an important reduction of fat-free mass characterized by the position of most individuals in the cachexia quadrant throughout the postoperative period. Copyright © 2014 Elsevier Inc. All rights reserved.