ABSTRACT: Background:Developing dietary strategies to prevent excess weight gain during childhood is critical to stem the current obesity epidemic and associated adverse cardiometabolic consequences. Objectives:We aimed to assess how participation in a family-based weight-management intervention affected nutrient biomarkers and cardiometabolic risk factors (CMRFs) in children (7-12 y old; n = 321) with baseline BMI z score (BMIz) ?85th percentile. Methods:This was a secondary analysis from a randomized-controlled, parallel-arm clinical trial. Families of children, recruited from a largely Hispanic population, were assigned to Standard Care (SC; American Academy of Pediatrics overweight/obesity recommendations), or SC + Enhanced Program (SC + EP; 8 skill-building cores, monthly support sessions, targeted diet/physical activity strategies). Nutrient biomarkers (plasma carotenoids, fat-soluble vitamins, RBC fatty acid profiles, desaturase indexes) and CMRFs were measured in archived blood samples collected at baseline and the end of the 1-y intervention. Results:Children in both groups had significantly lower trans fatty acid and higher pentadecylic acid (15:0), PUFA n-3, and ?-carotene concentrations, indicative of decreased hydrogenated fat and increased dairy, vegetable oil, fish, and fruit/vegetable intake, respectively. Similar changes were seen in de novo lipogenesis and desaturase indexes, as well as CMRFs (BMIz, lipid profile, inflammation, adipokines, liver enzymes) in both groups. Using multiple logistic regression, increase in carotenoids and decrease in endogenously synthesized SFA, MUFA, PUFA n-6, and desaturase indexes were associated with improvements in BMIz, blood pressure, lipid profile, glucose metabolism, inflammatory biomarkers, adipokines, and liver enzymes. Trans fatty acids were associated with improvements in BMIz, glucose metabolism, and leptin, with less favorable effects on inflammatory markers and adiponectin. Conclusions:Providing targeted family-based behavioral counseling, as part of SC, can help overweight/obese children adopt healthier eating patterns that are associated with modest improvements in BMIz and several CMRFs. Limited additional benefit was observed with SC + EP. These results provide critical data to design subsequent interventions to increase the impact of family-based obesity prevention programs.This trial was registered at clinicaltrials.gov as NCT00851201.