The aim of this study was to investigate the effect of protein intake during pregnancy on postpartum weight variation. This was a prospective cohort study with 421 women interviewed at 15 days (baseline) and 2, 6, and 9 months postpartum. Data on diet were obtained using the food frequency questionnaire, focusing on the second and third trimesters. Protein intake was considered adequate when women consumed > 1.2g of protein per kg body weight, and inadequate when < 1.2g/kg. The study adopted the mixed effects model for repeated measurements over time. The results showed a mean postpartum weight loss of 0.409kg/month (±0.12) (p < 0.01). Women with adequate protein intake during pregnancy lost an additional 0.094kg/month (±0.04) during postpartum (p = 0.03) when compared to women with inadequate intake. The model was adjusted for energy, % body fat, stature, age, schooling, skin color, and smoking. Recommended protein intake during pregnancy favored postpartum weight reduction.