Methods: In a randomized clinical design, 300 obese individuals, 12-18 years old, will be selected. At selection, individuals will be randomly assigned to receive daily a capsule with 1.1 g LCPUFA omega-3 during three mo together with a hypocaloric diet which follows the WHO recommendations (D+O3), or to receive daily a capsule with 1.0 g sunflower oil and a similar diet (P+D). After randomization, dietary information (24h-recall and FFQ), anthropometric measurements, and peripheral blood samples, will be obtained. Blood samples will be used to determine fasting plasma glucose and insulin, and erythrocytes fatty acid profile; such determinations will be repeated at three and six mo of follow-up. Anthropometry and 24 h-recalls will be repeated monthly.