Breastfeeding will make you lose the baby weight fast, they said. Just when you thought this was a win for womanhood, an RD explains why that isn’t always the case.

There’s a hell of a lot of pressure on moms to “bounce back” after giving birth, and no one knows that more than a royal new mom. When Meghan Markle stepped out for the first time with the fresh and delicious little Baby Sussex, there was as much chatter about her residual “baby bump” as her bundle of joy.

While a lot of moms (including me) applauded Meghan for rocking a belted trench that accentuated her postpartum bod (because hello, that’s real life), it was the follow-up comments I heard that made me cringe.

“Oh, that’s normal, but she’ll drop that weight so fast if she’s breastfeeding.”

Ah yes, I knew that promise all too well. I too was led to believe that breastfeeding was the equivalent of a less painful “Biggest Loser Challenge” at home (or maybe more painful if you had a baby-biter like me).

I was taught that with each session at the boob, those love handles and pooch belly would just melt away and I’d be rockin’ my pre-baby, pre-fertility treatments, and pre-wedding jeans in no time.

Heck, some moms in my Facebook groups told me they could fit back into their high school clothes, and yet, they barely even left their couch. Yes! Finally, a win for womanhood!

All of this mom-wisdom totally made sense to my science-driven mind as it’s estimated that you burn roughly 20 calories per ounce of breastmilk you produce. To put that into personal terms, for the bulk of my breastfeeding journey, I was pumping about 1,300 milliliters of breastmilk a day, which would equate to about 900 extra calories torched.

Do a little chicken-scratch math and I should have theoretically been dropping more than seven pounds every month without changing my diet or exercise regime. Forget Barry’s Bootcamp, just birth a baby and get them on the boob.

But alas, our bodies don’t operate like they would in calculus class, especially when there are hormones involved. Case in point — I’m a dietitian and the more I breastfed, the more my weight loss stalled, and I started to gain fat.

And I’m apparently not alone. A 2013 research review noted that the lion’s share of studies on breastfeeding and postpartum weight loss found that breastfeeding did not change the number on the scale.

Umm, what? After enduring morning sickness, insomnia, birth, and the brutality of a toothless newborn chomping at your raw torn nipple a dozen times a day, you would think the universe would cut us mamas some slack.

So, why is the math not adding up? Let’s look at the major reasons why breastfeeding isn’t the weight loss secret it’s promised to be.

Before the folklore of breastfeeding to lose weight came the idea that we need to “eat for two” during pregnancy. While that belief can make pregnancy appear more desirable, the Centers for Disease Control and Prevention tells us that most pregnant women only need about 340 extra calories in their second trimester and 450 extra calories in their third trimester.

Translation? That’s basically just a glass of milk and a muffin. Not surprisingly, according to a 2015 study, nearly half of pregnant women gained more weight than recommended during pregnancy, with a large review of studies linking this to an additional 10-pound weight retention 15 years later.

Arguably, not gaining enough weight, or dieting in general during pregnancy is even more problematic as it’s been linked to developmental issues and a risk of metabolic disturbances in the baby, and in severe cases, infant mortality.

So rather than calorie counting or treating each meal of those nine months like a marathon, I recommend simply focusing on listening to your body for those subtle shifts in hunger that accompany your increased needs.

I have always had a good-sized appetite, but nothing could prepare me (or my husband, or anyone else around me) for the raging hunger I experienced after giving birth. Within a day of my milk coming in, I immediately realized that my dainty bowl of steel cut oats with berries and a scant sprinkling of hemp hearts was just not going to silence my hunger beast.

In my dietetics practice, I would typically recommend that people pay close attention to their early hunger cues to avoid letting yourself get so ravenous, you inevitably overindulge. Well, until I felt I had a better handle on anticipating my Michael Phelps–like hunger, it wouldn’t have been hard to overshoot.

It’s also not uncommon for women to overeat in fear of losing their supply, as the advice in breastfeeding support circles is “eat like a queen” to “make it rain” milk.

As a dietitian who struggled hard with supply and breastfeeding in general, I would have happily overshot my needs any day of the week, accepting that holding onto some extra weight was well worth keeping up my supply.

Thankfully, you don’t have to be a mathematician to figure out your exact calorie needs — breastfeeding or not. You just have to listen to your body. By eating intuitively and responding to hunger at the earliest signs, you’re better able to align your consumption with your needs without frantically shoving all the food in at once.

We know this isn’t exactly a “lifestyle choice” right now, but chronic sleep deprivation never did anything good for maintaining a healthy weight.

Research has consistently shown that when we skimp on shut-eye, we see a boost in our hunger hormone (ghrelin) and a dip in our satiety hormone (leptin), causing appetites to surge.

To add insult to injury, scientists at the University of California also found that people who are sleep deprived tend to reach for higher-calories foods compared to their well-rested counterparts.

Practically speaking, there’s even more pieces to this unsettling story. In addition to a generally raging appetite and an undeniable craving for cupcakes at breakfast, a lot of us are also awake in the middle of the night with a crying, hungry baby.

And if you think you’re going to prepare yourself a balanced bowl of greens at 2 a.m. for a little nursing snack in your semi-deranged sleep-deprived state, you’re a different level of superhuman.

Cereal, salty nuts, chips, and crackers. Basically, if it was a shelf-stable carb I could keep by my bed, it was getting shamelessly shoved into my mouth before dawn.

Okay, so while we can all agree that female hormones can be the worst, they arguably are just doing their job to keep your breastfed babe fed. Prolactin, sometimes known affectionately as the “fat-storing hormone” is secreted postpartum to help stimulate milk production.

While research on this area of prolactin in sparse, countless lactation consultants, health practitioners, and disgruntled moms hypothesize that our bodies undergo metabolic adaptations to hold onto excess fat as “insurance” for the baby.

In other words, if you were temporarily stranded on a deserted island with no food, there will at least be something there to feed your babe.

When we consider the lack of sleep, postpartum pains, newborn challenges, shifting hormones, and the steep breastfeeding learning curve, it’s safe to say that the “fourth trimester” is stressful. Not surprisingly, researchers have found that overall life stress, and particularly maternal stress, is a significant risk factor for weight retention later post birth.

Research has also found that elevated cortisol levels (the hormone associated with stress) have been associated with weight retention in the first 12 months postpartum.

I wish I had an easy suggestion for how to unwind, but realistically, it’s often a bit of a crapshoot for those first few months. Try to carve out some “you” time by getting your partner, friend, or family to help out. And just know, there’s a light at the end of the tunnel.

A lot of women don’t find their breastfeeding journey easy or “natural” at all, turning to medication and supplements to boost their supply. Both metoclopramide (Reglan) and domperidone (Motilium) are commonly prescribed to moms as off-label lactation aids, but in the general population, are used to treat delayed gastric emptying.

Unfortunately, when you take these meds without gastric emptying issues, you get really hungry, really fast. As if breastfeeding alone wasn’t enough to force you to just park yourself permanently in the pantry, there’s a drug that makes you need to eat all.of.the.time.

Not surprisingly, weight gain is a common side effect of taking the drugs, and most women claim they can’t start losing any baby weight until they wean themselves off the meds.

I assumed I would lose weight when I got off domperidone, but by then it was like my body had downgraded its hunger cues and I didn’t notice anything on the scale. Then, about a week after I pumped my last bottle of milk, I woke up and my whole body had leaned out. I also found myself noticeably less hungry, so I wasn’t interested in snacking all day.

Most significantly, though, I just felt a wave of energy and happiness I hadn’t experienced in nearly two years. It was one of the most freeing weeks of my life. So, while yes, there are often multiple factors at play when it comes to body weight regulation, I’m a big believer that your body has a “set point” that it settles into naturally when your sleep, hormones, and diet are well balanced and aligned.

The best advice I can give to myself in the hopeful event of round two is to listen to my body, fuel it to the best of my ability with nourishing foods, and be kind to myself through this unique phase of life.

Breastfeeding, like pregnancy, is not the time to diet, cut calories, or go on a cleanse (not that there’s really any a good time for that). Keep your eye on the prize: that squishy milk-drunk babe. This phase will pass.

Abbey Sharp is a registered dietitian, TV and radio personality, food blogger, and the founder of Abbey’s Kitchen Inc. She is the author of the Mindful Glow Cookbook, a non-diet cookbook designed to help inspire women to rekindle their relationship with food. She recently launched a parenting Facebook group called the Millennial Mom’s Guide to Mindful Meal Planning.