I've heard this idea since having a baby that breastfeeding will help you lose all the pregnancy weight no sweat. Several women have approached me wide-eyed, all "breastfeeding burns so many calories! I hear it's great for weight loss!"
Everyone's different, and I do know a lot of women who lost some weight while nursing. After all, breastfeeding burns a bunch of calories a day.
What they don't tell you is that the energy expenditure of nursing -- creating milk and giving it to your baby -- makes you RAVENOUS. I have never eaten as much in my life as I did the first weeks post-partum. I would wake up in the middle of the night to feed the baby, and my stomach was flat-out hurtling after the refrigerator.
Also, lady, you're sleep-deprived in a way you've never been before, and sleep-deprived people love carbs. It's what our bodies crave when we have no energy.
So all that to say that after the first big drop in weight from birth and fluid loss and, you know, not having a whole person inside my body anymore, I didn't lose weight during breastfeeding. Like, at all.
Around month 3, my appetite stabilized, along with my milk supply. But even then, I didn't lose any weight, from what I could tell. I wasn't weighing myself (kind of allergic to scales over here), but I had a couple of doctor's appointments where they weighed me, and my clothes didn't fit any differently. And lest you think I was still eating like a teenage football player, I wasn't. It was about the same that I'd eaten before I was pregnant.
So, all this to say that if you're counting on breastfeeding being the big panacea of weight loss, be careful with that expectation. It may not turn out that way. And even if it does, it seems that many women start to gain weight back when they stop breastfeeding.
If you're mad about this, it might help to know that now that my baby is getting close to weaning, I have dropped some weight. I don't care much about it, honestly. But I'm just putting it out there. I might be one of the women who loses weight after breastfeeding, because (a) not eating as much, naturally (b) breastfeeding also takes time and commitment. now that I'm doing it less, I have time to do things like yoga and going to the gym (c) hormones may have some role in all of this. I don't know for sure, but hormones can be blamed for a lot of craziness, so let's not discount them.
So all this to say that the best thing, once again, is changing your lifestyle (as much as one can with a tiny person in your life) to be sustainable and affirming For You, whatever that looks like. The weight loss may or may not happen. But I do know that moving my body, and eating stuff that feels right for me, and getting massages, and doing a bunch of yoga has me feeling better than I have in months/years. And that's a reward in and of itself.