Women who breast-feed their babies tend to lose weight gained during pregnancy more quickly than those who don't breast-feed their babies, according to a study published in the American Journal of Clinical Nutrition in December 2008. This is because your body uses a significant number of calories to create the breast milk you're giving to your baby.
While you are breast-feeding, your body needs between 200 and 500 calories per day more than you did before you got pregnant, according to KellyMom.com. Whether you breast-feed exclusively, how old your baby is and your weight before pregnancy can all affect how many extra calories you need to provide your baby with breast milk.
Losing more than 1.5 pounds per week or cutting calories below 1,500 to 1,800 calories per day can decrease your milk supply. So can a large, sudden drop in the number of calories you consume or cutting calories within the first two months after delivery. When increasing calories to cover those needed for breast-feeding, do so by eating more nutritious foods, not junk foods, as more of the essential nutrients are needed to make breast milk, not just more calories.