Depends. If you look at the specifics, creating breast milk for baby requires metabolic work on your part ( that is quite passive).Over 1yr your breasts will use your body energy to create roughly 500-1000 cal/day for baby. If you only consume the diet you need for your pre-pregnancy weight, you could drop 1-2 pounds a week due to breastfeeding alone.If you eat more you loose less.
Yes. A new mom will lose weight as long as she breastfeeds her baby, and she eats only as many calories as needed to maintain her pre-pregnant weight. For example, if she was 120 pounds before pregnancy and is now 145 pounds, she should eat just enough for a 120 lb woman. Her 25 lb excess will be gradually used up in the production of breastmilk (25 ounces of breastmilk contains about 500 calories).