Postpartum Weight Loss and Breastfeeding
by Anne Eglash MD, IBCLC, FABM
Intuitively it makes sense that women would lose weight when breastfeeding, because it is estimated that women burn approximately 500 calories a day by breastfeeding. However, the studies on breastfeeding and weight loss are mixed. One reason is because women who breastfeed longer tend to have health and social characteristics that are associated with a lower BMI before becoming pregnant. This means that it has been hard to sort out if the weight loss is due to behavior and genetics, or actually breastfeeding.
The research for this week’s CQW is a study that looked at postpartum weight loss associated with breastfeeding. The data was derived from 370 mother infant dyads from the Mothers and Infants Linked for Healthy Growth (MILK) study, conducted in the Midwest United States. The mothers’ breastfeeding status was categorized at 1, 3, and 6 months postpartum as fully breastfeeding, mixed-feeding, or fully formula feeding.
Maternal weight was measured within the first 6 weeks of pregnancy, then at 1, 3, and 6 months postpartum.
Demographic data was also collected on the mothers, including education, income, physical activity, dietary intake, age, type of delivery, infant birthweight and infant gender.
- Mothers who fully breastfed for longer than 3 months had significantly greater weight loss than mothers who fully breastfed for less than 3 months, after controlling for the demographic factors.
- Women with a low pre-pregnancy weight have a harder time losing the weight gained during pregnancy despite fully breastfeeding.
- There was no significant difference in weight loss between women who fully breastfed for 6 months or longer, vs those who breastfed for 3-6 months.
- An elevated prolactin level helps to prevent the manufacturing of fat in areas where fat is stored, favoring fat manufacturing for milk in the lactating breast.
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Full breastfeeding (FBF) is promoted as effective for losing pregnancy weight during the postpartum period. This study evaluated whether longer FBF is associated with lower maternal postpartum weight retention (PPWR) as compared to a shorter FBF duration. The MILK (Mothers and Infants Linked for Healthy Growth) study is an ongoing prospective cohort of 370 mother–infant dyads, all of whom fully breastfed their infants for at least 1 month. Breastfeeding status was subsequently self-reported by mothers at 3 and 6 months postpartum. Maternal PPWR was calculated as maternal weight measured at 1, 3, and 6 months postpartum minus maternal prepregnancy weight. Using linear mixed effects models, by 6 months postpartum, adjusted means ± standard errors for weight retention among mothers who fully breastfed for 1–3 (3.40 ± 1.16 kg), 3–6 (1.41 ± 0.69 kg), and ≥6 months (0.97 ± 0.32 kg) were estimated. Compared to mothers who reported FBF for 1–3 months, those who reported FBF for 3–6 months and ≥6 months both had lower PPWR over the period from 1 to 6 months postpartum (p = 0.04 and p < 0.01, respectively). However, PPWR from 3 to 6 months was not significantly different among those who reported FBF for 3–6 versus ≥6 months (p > 0.05). Interventions to promote FBF past 3 months may increase the likelihood of postpartum return to prepregnancy weight.
Women with a low pre-pregnancy weight have an easier time losing their weight gained during pregnancy.
We have not been able to state unequivocally that breastfeeding is associated with postpartum weight loss, even though breastfeeding mothers burn more calories than mothers who don’t breastfeed. However, in this study, the difference in weight loss between the mothers who breastfed for less than 3 months compared to those who breastfed for longer than 3 months is impressive.
I find that some breastfeeding patients share their dietary indulgences, knowing that they have calorie latitude, while others ask me when they can start working on postpartum weight loss. They share their concerns about a drop in their milk supply if they lose weight too quickly. I suspect that we might observe more consistent postpartum weight loss in breastfeeding mothers if we provide nutritional guidance to help them lose weight by not overeating while lactating.
On the other hand, I know that a minority of lactating mothers try so hard to lose weight while nursing, and the weight won’t come off until they wean. Perhaps it is this unclear hormonal phenomenon that factors into the mixed study results on the role of breastfeeding in postpartum weight loss.