Typically, studies have shown that breastfeeding women tend to lose weight more rapidly than their formula feeding counterparts. (Bradshaw & Pfeiffer, 1988, Kramer et al 1993, Dewey et al 1993) In one study breastfeeding mothers were back to their pre-pregnancy weight by six months, whereas the formula feeding women were not. (Kramer et al 1993)

Weight gained with a pregnancy generally comes off more readily in the second six months after your baby is born than during the first six months. (Dewey et al) Mothers who exclusively, and more frequently, breastfeed over a longer period of time will generally lose more weight than women who breastfeed shorter periods of time and supplement with formula. It was also found that women who were overweight before pregnancy tended to lose less weight in the postpartum period than women who were not overweight prior to pregnancy.(Riordan & Auerbach 1999)

It doesn't seem likely that breastfeeding intrinsically inhibits weight loss or induces weight gain after the birth of a baby. However, I wonder if the stresses of being a new mom may make some new mothers especially vulnerable to weight problems. Overeating is a common reaction to stress. Additionally, mothers of young children often just grab whatever food is handy, usually high-calorie treats and prepared foods.

You may find it helpful to keep a food diary to record everything you eat. I would also recommend a trip to your care provider to rule out any medical causes of your extra pounds. He or she may also recommend a visit with a registered dietician to help evaluate your diet and guide you toward reasonable changes.

Weight loss during lactation is best attained by lowering fat in the diet and exercising. Most women can safely lose about one pound per week while breastfeeding. Women eating about 2200 calories a day, a calorie reduction of about 25 percent, will usually lose weight. A breastfeeding mother should not reduce her calories lower than 1800 calories a day. Dietary adjustments can also safely be enhanced with a moderate exercise program. You should avoid any crash or fad diets that restrict you to single food groups or encourage very rapid weight loss. (Riordan & Auerbach 1999)

References:

• Bradshaw MK, & S. Pfeiffer "Feeding mode and anthropometric changes in primiparas". Hum Biol 60:251-261, 1988
• Dewey K, et al, "Maternal weight-loss patterns during prolonged lactation" American Journal of Clinical Nutrition 58: 162-166, 1993
• Kramer, F. et al, "Breastfeeding reduces material lower-body fat" Journal of American Dietetic Association, 93:429-33, 1993.
• Riordan, J. and K. Auerbach, Breastfeeding and Human Lactation, Jones and Bartlett, Boston, 1999. pp 518-519.