Moms who breastfeed have lower
estrogen and testosterone levels.

Both hormones boost fat burning. Their progesterone and prolactin (the milk production hormone) levels are higher - both block the ability to burn fat. 

Additionally, breastfeeding moms who eat a diet high in dairy, grains and sugar will find it very hard to lose fat. Here’s why: Starches, sugar and dairy trigger an insulin response by the body. Insulin signals the body to store fat. Dairy contains high levels of progesterone, estrogen and prolactin (among other hormones), so the combination of the mom’s own hormones paired with the external hormones of an insulin-stimulating diet puts her into fat storage mode, regardless of how little she may eat and how much she may exercise. 

The key to boosting fat loss during this hormonally more challenging period is to focus your carbohydrate intake on fibrous carbs from veggies and to reduce or eliminate dairy. Regular protein intake quiets the appetite. It is also important to exercise regularly as that keeps the body sensitive to insulin, meaning that it can actually burn the carbs that are coming in and not shuttle them into fat storage. 

The good news is that studies have shown that fat loss while breastfeeding may not be as fast as you want, but once you’re done breastfeeding, it is actually faster compared to women who never breastfed. Women who bottle-fed their babies lose weight faster initially, but after 3 months are surpassed by the women who breastfeed their babies. Even better, women who breastfeed have less belly fat, leaner thighs and are able to maintain that effect on their bodies, when compared to bottle-feeding moms.