Objective: Previous studies have found that breastfeeding may protect infants against future overweight. One proposed mechanism is that breastfeeding, as opposed to bottle feeding, promotes maternal feeding styles that are less controlling and more responsive to infant cues of hunger and satiety, thereby allowing infants greater self-regulation of energy intake. The objective of this study was to determine the extent to which the protective effect of breastfeeding on future overweight is explained by decreased maternal feeding restriction.

Patients and methods: We studied 1012 mother-infant pairs in Project Viva, an ongoing prospective cohort study of pregnant mothers and their children. The main exposure was breastfeeding duration, assessed at 1 year postpartum. At 3 years of age, the main outcomes were age- and gender-specific BMI z score and the sum of subscapular and triceps skinfold thicknesses, with overweight defined as a BMI > or = 95th percentile. We defined maternal restriction of infant's access to food as strongly agreeing or agreeing, with the following question from the Child Feeding Questionnaire: "I have to be careful not to feed my child too much." To examine the association between breastfeeding duration and our outcomes, we used multivariate linear and logistic models, adjusting for several potential confounders. In subsequent models, we also adjusted for maternal restriction of infant's access to food.

Results: The mean duration of breastfeeding was 6.5 months, and 12% of women strongly agreed or agreed with the restriction question. At age 3, mean for BMI z score was 0.47. Each 3-month increment in breastfeeding duration was associated with a reduction of 0.045 BMI z score. After adjusting for maternal restriction, the estimate was -0.039, a 13% attenuation.

Conclusion: The protective effect of breastfeeding on future overweight seems to be explained only partially by decreased maternal feeding restriction.