Background and objective: The aim of our work was to evaluate in obese patients with an indication of replacement surgery for degenerative osteoarthritis, the utility of a hypocaloric diet with Optisource (R) vs nutritional counseling. Material and method: Thirty six patients were randomized in both branches: diet I with lunch and dinner substituted by two Optisource (R) (1109,3 kcal/day, 166,4g of carbohydrates (60%), 63 g of proteins (23%). 21,3 g of lipids 17%) and diet II with nutritional Counselling with a decrease of 500 cal/day from the previous dietary intake. Before and 3 months after treatment, a nutritional and biochemical Study was performed. Results: Nineteen patients were randomized in group I and 17 patients in group 11.19 patients finished the study in group I and 14 in group II. Weight loss was higher in group I than 11 (7,7 [4,7] vs 3,92 [3,32] kg; P=.05), with a significant decrease of HOMA and diastolic blood pressure in group I. Decreases of body mass index (-2,9 [1,8] vs -1,4 [0,9]: P=.05), fat mass (-3,8 [3,4] vs -2,3 [1,7] kg; P=.0,05) and HOMA (-2,0 [2,2] vs -0,4 [1,82]; P =.05) were higher in group I than II. Conclusions: Obese patients with chronic osteoarthritis treated with a mixed diet Supplemented with a commercial hypocaloric formula improved weight, fat mass and HOMA in a better way than patients treated with a dietary counselling alone. (C) 2008 Elsevier Espana, S.L. All rights reserved.