You can lose weight while breastfeeding by creating a calorie deficit (burning more calories than taking in). You are expending energy just by breastfeeding. So if you take in the recommended number of calories for a non-breastfeeding parent—up to 2,000 calories per day if you're sedentary and up to 2,400 if you are active—you should lose weight gradually. Regular aerobic exercise—like vigorous walking, jogging, biking, or a cardio class—boosts fitness and heart health in people who are lactating. Feed your baby right before exercise to relieve engorgement and reduce discomfort.