The Association between the 2009 WIC Food Package Change and Early Childhood Obesity Risk Varies by Type of Infant Package Received

Background In 2009, the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) food packages were updated. WIC-participating children in Los Angeles County receiving the new food package, compared with the old, had lower obesity risk at age 4. Objective To determine if the association between the new WIC food package and obesity varies by type of infant WIC food package received. Design Longitudinal study using administrative data on children participating in WIC in Los Angeles County continuously from birth until age 4. Children were compared across periods: Before (period 1: born 2003-2004), straddling (period 2: born 2005-2008), and after (period 3: born 2009-2011) the food package change. Children were further grouped as Fully Breastfed, Mostly Breastfed, Mostly Formula Fed, and Fully Formula Fed based on the type of food packages received during the first year of life. Participants/setting WIC-participating children in Los Angeles County between 2003 and 2016 (N = 116,991). Main outcome measures Weight-for-height z-score growth trajectories from 0 to 4 years and obesity (body mass index-for-age >= 95th percentile) at age 4. Statistical analyses performed Children were matched across periods on infant feeding group; age, sex, race or ethnicity, and initial weight status; maternal education and language; and family poverty. Sex-stratified piecewise linear spline mixed models and Poisson regression models were fit to the data. Results No differences across periods were observed for children in the Fully Breastfed group. Boys in the Mostly Breastfed (relative risk [RR] = 1.27, 95% CI = 1.17 to 1.38), Mostly Formula Fed (RR = 1.07, 95% CI = 1.02 to 1.13), and Fully Formula Fed (RR = 1.13, 95% CI = 1.06 to 1.20) groups in period 1 had higher obesity risk than their counterparts in period 3; girls in the Mostly Breastfed group in period 1 had a higher obesity risk than those in period 3 (RR = 1.17, 95% CI = 1.07 to 1.28). Conclusions The association between the WIC food package change and obesity varied by type of infant food package received, with the strongest associations observed for those who were mostly breastfed.