Breastfeeding and Calorie Needs
Breastfeeding mothers need at least 1,500 to 1,800 calories just to function, with 1,500 being the absolute minimum amount you must take in. Research has shown that mothers who eat fewer than 1,500 calories a day experience a drop in milk supply. Many women will find that 1,500 calories aren't nearly enough to keep them feeling satisfied through a busy day of caring for an infant.
The resting metabolic rate for an average thirty-year-old woman who is 5 feet, 5 inches tall and weighs 135 pounds is 1,400 calories. That means that a woman of that age, height, and weight needs to consume 1,400 calories per day just to support her body's vital functions — nothing else.
You'll need 200 to 500 calories or more for breastfeeding. Add in the number of calories you'll burn just existing, and then consider that, as the mother of a small baby, you'll be doing a lot more than just existing, and you'll see that the “necessary” 1,500 calories is very much on the low end for most women.