The study, conducted by researchers at the Department of Agriculture, Food & Nutritional Sciences in Alberta, Canada, used a small sample of 50 women who reported their pre-pregnancy weight and their highest weight during pregnancy. After giving birth, women were divided into groups based on whether they were breast-feeding or not. The breast-feeding women were asked to keep feeding diaries, and for both groups, height, weight, and BMI were recorded periodically.
By three months postpartum, there was no difference in weight loss or body-fat percentage across the two groups. The strongest determinant of postpartum weight loss was pre-pregnancy BMI: The lower the BMI before giving birth, the more likely the women were to lose weight in the three-month postpartum period.
So if you’re looking to breast-feeding as a quick way to lose weight, you might need another strategy — like working out in your free time. Although, dieting is not recommended to do while breastfeeding.