For many years we all have listed "faster weight loss" as a benefit of breastfeeding for the mother. Yet a visit to any La Leche League International conference will demonstrate that the incidence of overweight and obesity in that population is no different than the general population - it is too high in both! Does breastfeeding really improve postpartum weight loss?

Kathryn G. Dewey PhD, of the Department of Nutrition, University of California, Davis, has recently completed a review of the literature to try to answer this very question. This summary is taken, with permission, from her paper presented at the International Society for Research in Human Milk & Lactation (ISRHML) meeting in Mexico in 2002. The paper is currently in press (in "Protecting Infants through Human Milk: Advancing the Scientific Evidence Base," Kluwer Publishers, 2003).

Theoretically, if there were no increase in maternal energy intake during lactation, as compared with a woman's normal intake when not pregnant or lactating, weight loss for every breastfeeding woman would be rapid and dramatic, on the order of 13 kg (28.6 lbs) over the first 6 months postpartum. As this rarely happens, there must be compensatory factors, such as decreased activity or increased appetite due to increased prolactin levels, to maintain body weight.

Most of the data have come from observational studies, which are subject to multiple confounding variables, such as maternal age, ethnicity, education, income, pre-pregnancy weight, pregnancy weight gain, parity, inter-birth interval, physical activity and dietary practices. Observational studies also suffer from varying methods and timing of assessing the outcome variable: weight or body mass index (BMI). Perhaps the biggest problem is the one all breastfeeding studies face - the definition of breastfeeding. Both duration and exclusivity of breastfeeding may be important factors in weight loss. Dr. Dewey found 6 studies that met quality criteria, had a precise definition of breastfeeding, and actually measured postpartum weight change.

Dr. Dewey came up with 3 tentative conclusions from her review of the literature. First, she found evidence for a dose-response relationship between the degree of breastfeeding and the degree of weight loss. Second, the greatest weight difference between lactating and non-lactating women was found at 3-6 months postpartum. Finally, although breastfeeding does appear to enhance the rate of weight loss, at least during certain time intervals, the magnitude of this effect is small compared with other factors such as pregnancy weight gain, dietary practices and physical activity. The average difference in weight loss by 12 months postpartum between lactating and non-lactating women was about 0.6 to 2.0 kg (1.3-4.4 lbs).

There are many wonderful benefits of breastfeeding for the mother. A modest weight loss may be one of them. We certainly should not put it at the top of the list!