There is a perception that one of the benefits of breastfeeding is weight loss. This premise makes sense since at least 500-1000 calories are expended in breast milk production. That’s like running five to ten miles! Based on the current data that it takes 4500 calories to burn a pound of fat, one would expect to lose one pound every nine days. Unfortunately, that amount of weight loss is rarely the case.
Breastfeeding has known benefit for reducing excessive weight in newborn children, especially when those babies were directly breastfed, rather than fed breast milk from a bottle. As a result, the American Academy of Pediatrics advocates for breastfeeding, and one of those benefits is the “reduction of child overweight and obesity.” One mechanism may be that leptin is contained in breast milk, with the highest levels early in lactation. Yet, since leptin is a large protein, the absorption of leptin into an infant’s bloodstream is uncertain.
How about the breastfeeding mom? A study on 2100 postpartum women showed that those who exclusively breastfed their newborns only lost 3.2 pounds more than those who did not at one year. That is far less than one would expect. Why is it so difficult to lose weight while breastfeeding? The answer may lie in the increase in appetite many moms report. We know that exercise without changing dietary intake rarely leads to significant weight loss. Many breastfeeding women report voracious appetites, as is confirmed subjectively by many lactation blogs. Women often report great difficulty losing weight while breastfeeding. While the benefits of breastfeeding are great, weight loss may not be one of them.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4312189/
https://pediatrics.aappublications.org/content/142/4/e20181092