To examine the association between breast-feeding duration and the risk of excess body weight (children >85th percentile, mothers BMI≥25·0 kg/m2) concurrently in mother–child pairs two years after delivery.

Prospective cohort study in Joinville, Brazil. Multivariable logistic regression was used to examine the independent relationship between breast-feeding duration and risk of excess body weight.

Brazilian public maternity hospital.

Three hundred and five mother–child pairs.

At 2-year follow-up, 23·6 % of mother–child pairs had excess body weight. Children breast-fed for <2 months were more likely to have excess body weight than children breast-fed for ≥6 months (OR=2·4; 95 % CI 1·1, 5·1). Breast-feeding for <2 months was also associated with a greater likelihood of maternal excess body weight compared with those who breast-fed for ≥6 months (OR=2·9; 95 % CI 1·1, 8·1). There was a progressive increase in the likelihood of mother–child pairs having excess body weight as breast-feeding duration decreased. In addition to breast-feeding duration, other independent determinants of excess body weight were pre-pregnancy weight, gestational weight gain and number of pregnancies in mothers, and birth weight in children.

Breast-feeding for a longer duration has a parallel protective effect on the risk of excess body weight in mother–child pairs two years after birth. Since members of the same family could be influenced by the same risk factors, continued promotion and support of breast-feeding may help to attenuate the rising prevalence of overweight in mother–child pairs.

We examined whether breast-feeding, and in particular exclusive breast-feeding, was associated with maternal weight and body composition changes at 4 months postpartum independently of other maternal variables.

Prospective longitudinal study. Women were recruited in the first trimester after an ultrasound examination confirmed an ongoing singleton pregnancy. Weight and body composition were measured using advanced bio-electrical impedance analysis at the first antenatal visit and 4 months postpartum. Detailed questionnaires were completed on breast-feeding, socio-economic status, diet and exercise in addition to routine clinical and sociodemographic details.

Large Irish university maternity hospital.

Women who delivered a baby weighing ≥500 g between November 2012 and March 2014.

At the postpartum visit, the mean weight was 70·9 (sd 14·2) kg (n 470) and the mean BMI was 25·9 (sd 5·0) kg/m2. ‘Any breast-feeding’ was reported by 65·1 % of women (n 306). Irish nativity (OR=0·085, P<0·001), current smoking (OR=0·385, P=0·01), relative income poverty (OR=0·421, P=0·04) and deprivation (OR=0·458, P=0·02) were negatively associated with exclusive breast-feeding. At 4 months postpartum there was no difference in maternal weight change between women who exclusively breast-fed and those who formula-fed (+2·0 v. +1·1 kg, P=0·13). Women who exclusively breast-fed had a greater increase in percentage body fat at 4 months postpartum compared with women who formula-fed (+1·0 v. −0·03 %, P=0·02), even though their dietary quality was better. Exclusive breast-feeding was not associated with postpartum maternal weight or body fat percentage change after adjusting for other maternal variables.

There are many reasons why breast-feeding should be strongly promoted but we found no evidence to support postpartum weight management as an advantage of breast-feeding.