Impact of early rapid weight gain on odds for overweight at one year differs between breastfed and formula-fed infants

Background Early rapid weight gain (RWG) increases, whereas longer durations of breastfeeding decreases, odds for later obesity. Objectives To determine the independent and interactive effects of early weight gain and diet on infant weight status trajectories and odds for overweight at 1 year. Methods We conducted secondary analysis on data from two longitudinal trials with repeated anthropometric measures. One trial consisted of predominantly or exclusively breastfed (BF,n= 97) infants, whereas the other consisted of exclusively formula-fed (FF,n= 113) infants. Weight-for-length z-score (WLZ) change from 0.5 to 4.5 months was used to categorize early weight gain as slow (<-0.67; SWG), normal (-0.67 to 0.67; NWG) or rapid (>0.67; RWG). Linear-mixed effects models were fit to examine the independent effects and interaction of early diet (BF, FF) and weight gain (SWG, NWG, RWG) groups on WLZ trajectories; logistic regression was used to assess odds for overweight at 1 year. Results While similar percentages (41%) of BF and FF infants experienced RWG, we found a significant diet x early weight gain group interaction (P < .001) on weight status. At 1 year, the WLZ of FF infants with RWG (1.57 +/- 0.99) was twice that of BF infants with RWG (0.83 +/- 0.92). Using BF infants with NWG as the reference group, FF infants with RWG had increased odds [OR: 25.3 (95% CI: 3.21, 199.7)] for overweight at 1 year, whereas BF infants with RWG did not. Conclusions Early diet interacts with early weight gain and influences weight status trajectories and overweight risk at 1 year.