Excessive gestational weight gain and postpartum weight retention are risk factors for female obesity. The present study was to examine dietary intakes and weight history from a prospective follow-up study from early pregnancy to 1 year postpartum. A total of 151 pregnant women within 20 weeks of pregnancy in Taipei, Taiwan were interviewed periodically to collect dietary and lifestyle information. The participants had an average age of 30 years and the average gestational weight gain was 14 kg, with an average daily intake of 7830 kJ (1870 kcal) in the 1 year following parturition. By bivariate analyses, maternal age, pre-pregnancy BMI and breast-feeding were not related to postpartum weight retention, but gestational weight gain had significant positive correlations (r 0·54 at 6 months, r 0·44 at 1 year; P < 0·05). The generalised estimating equations showed that the average weight before pregnancy, at 6 months and 1 year postpartum was 53·35 kg, 55·75 kg (weight retention 2·36 kg; P < 0·01) and 54·75 kg (weight retention 1·48 kg; P < 0·01), respectively. After controlling for age, pre-pregnancy BMI, gestational weight gain and parity, we found at 6 months that the adjusted weight retention at postpartum was 0·79 kg (P < 0·01), but at 1 year it was − 0·08 kg (P>0·05). From multivariate analyses, dietary energy intake and energy intake per kg body weight as a long-term physical activity index could explain 24 % of the variation at 6 months and 27 % of the variation at 1 year in postpartum weight retention. These results suggest that pregnant women should be advised to control gestational weight gain, decrease energy intakes after child-bearing and maintain regular exercise in order to prevent postpartum obesity.