The 2009 Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) food package change and children's growth trajectories and obesity in Los Angeles County

Background: In 2009, for the first time since the program's inception in 1974, the Special Supplemental Nutrition Program for Women, Infants and Children (WIC) changed their food packages, providing food options better aligned with the 2005 Dietary Guidelines for Americans. Objective: The aim of this study was to evaluate whether the 2009 WIC food package change was associated with changes in growth trajectories from age 0 to 4 y or obesity at age 4 among children who participated in WIC in Los Angeles County between 2003 and 2016. Methods: Children were grouped into 1 of 4 exposure groups: full-dose, new food package group (participating in WIC from birth to age 4, post 2009, N = 70,120), full-dose, old food package group (participating from birth to age 4, pre 2009, N = 85,871), late-dose, new food package group (participating from age 2 to 4 y, post 2009, N= 8386), and late-dose, old food package group (participating from age 2 to 4 y, pre 2009, N = 18,241). Children were matched across groups on gender, race/ethnicity, maternal education and language, family income, and initial weight status, and matched analyses were performed. Longitudinal growth trajectories were modeled using piecewise linear spline mixed models, and differences in obesity at age 4 were compared using Poisson regression models. Results: Children receiving a full dose of the new food package had healthier growth trajectories and a lower obesity risk at age 4 than children receiving a full dose of the old food package (RR [95% CI]: 0.88 [0.86, 0.91] for boys, 0.90 [0.87, 0.93] for girls). Boys, but not girls, in the late-dose, new food package group had a lower obesity risk at age 4 compared with boys in the late-dose, old food package group (RR = 0.89, 95% CI = 0.81, 0.98). Conclusions: The WIC food package change appears to be associated with improved childhood obesity outcomes. These findings are important in informing policymakers considering further improvements to the WIC food packages.