When I decided to start trying to lose weight after I had my first baby, I was exclusively pumping for my son and was concerned that trying to lose weight would impact my milk supply. I also wasn’t sure how many extra calories I needed for breastfeeding. After doing some research, I figured out a formula to calculate the exact number of calories I was burning by pumping breast milk.

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When I was pregnant with my son, I gained 55 pounds, which is 20-30 pounds over the recommended weight gain. I think part of the reason behind this was that I was really hungry all of the time, part of it was water, and a lot of it was due to “eating my feelings.”

I had had 3 miscarriages before my first child was born – one of them after the first trimester – so I had a lot of anxiety about my little one that I dealt with in the form of ice cream.

So when my son was born, I felt gross and wanted to lose the baby weight as quickly as possible. During the first month postpartum, I lost the 10ish pounds that constituted the baby, placenta, and amniotic fluid, plus another 20 or so pounds of water.

That left me with about 25 pounds to lose, and I wanted to do it as quickly as possible – but I wasn’t sure exactly what the “rules” were. Here’s the info I came up with after hours upon hours of searching the internet for evidence-based answers.

How many extra calories do you burn when you’re making milk?

Many breastfeeding resources will tell you that you burn an extra 300-500 calories while breastfeeding. When it comes to weight loss, vagueness like this drives me crazy. Personally, I do much better with a very specific understanding of what I am burning and, therefore, how much I should be eating.

A vague “300-500” calories when I’m starving is really frustrating, because I don’t know if I can really have that extra 200 calories and still be successful in losing weight.

Here is one area where exclusively pumping actually has its advantages! Because you are pumping and therefore able to easily and accurately measure your milk output, you know exactly how many ounces (or milliliters) of milk you are producing.

Therefore, it’s very easy to calculate of your caloric output from milk – each ounce of breast milk has 20 calories (10 mls has 6.8 calories), and this energy isn’t spontaneously created in your boobs. So, if you pump 20 ounces per day, you are using 400 additional calories to feed your baby. If you are pumping 30 ounces, then 600 calories, and so on.

At one point with my son, I was pumping 50 ounces per day, which is 1,000 calories of milk produced. That is an awful lot more than that 300-500, which would explain why I was so freaking hungry and also why the vagueness made me insane.

So an easy way to determine a basic estimate of how many extra calories you are burning due to breastfeeding is take your total pumping output for the day and multiply it by 20.

Now, if you’re not an exclusive pumper and want to determine how much milk you’re making, you have a few options:

Take one day where you weigh your baby before and after every feeding using a scale like this. Subtract the before weight from the after weight to determine how much your baby ate. At the end of the day, total the baby’s intake from all the feedings, multiply it by 20, and you have a good estimate!

Pump and bottle feed your baby for 24 hours and then multiply the number of ounces you pump by 20.

Want to get even more precise?

Multiplying by 20 does not take into account the energy that is required to actually make the milk. Making milk is a bodily function that needs fuel. After I initially wrote this post, a reader studying for her lactation consultancy exams wrote in to tell me that the production efficiency (or the amount of energy needed to make milk) is 80% of the energy produced. I was able to find other studies that back up this number.

Therefore, the total calories that you burn by breastfeeding are the calories in the milk plus the energy required to produce the milk.

How Many Calories Does Pumping Burn? Breastfeeding Calorie Burn Calculation Formula

Here’s an example. If you pump 20 oz, you would multiply that by the 20 calories that is in the milk, and then divide that by .8 (the production efficiency) to get the total calories burned by breastfeeding (including the milk you make AND the energy you burned making the milk). So your total calorie burn from breastfeeding would be:

(20 oz * 20 calories)/0.8 = 500 total breastfeeding calories (400 calories from the breast milk itself; plus an additional 100 in energy to make the milk)

So just plug your number of ounces in the below breastfeeding calorie burn calculation formula:

(# of oz * 20)/0.8 = Total Breastfeeding Calories

Here’s the metric system version:

(# of ml * .68)/0.8 = Total Breastfeeding Calories

Does Pumping Burn the Same Amount of Calories as Nursing?

The only thing that matter is the amount of breast milk that is produced.

So, say you’re nursing your baby and she nurses like a champ, but your body doesn’t respond well to the pump and you don’t pump much milk when you’re at work. You would burn fewer calories at those pumping sessions than you would if you were nursing then, because you are producing less milk.

On the other hand, say you’re exclusively pumping and have a large oversupply. You’re burning MORE calories that you would if you if you were nursing, because you’re producing more milk than your baby would otherwise eat.

Four Challenges Breastfeeding Moms Face When Losing Weight

There are some things that make postpartum weight loss different (and harder!) as compared to “normal” weight loss – especially when you are nursing or exclusively pumping. Here are the big ones.

Challenge #1: Hormones

New moms seem to fall into one of two categories when it comes to losing weight while breastfeeding*:

Mom loses weight quickly and easily and can eat whatever she wants until she weans. (She may then gain some weight if she doesn’t adjust her intake appropriately.)

Mom loses a decent amount of baby weight but holds onto an extra 5-10 pounds until she weans.

* This is based on my own experience, my friends’ experiences, and what I’ve learned spending way too much time reading parenting message boards.

Personally, I fell into the first category with my son and am in the second category with my daughter. Need I say that the first is better? If you’re in the first group, yay! If you’re in the second, there is not much that you can do except realize that this is not uncommon and the issue should hopefully resolve itself when you wean. You also might want to consider how much effort you want to put into losing the remaining baby weight given that your hormones are fighting you and that this is likely temporary.

Challenge #2: Raging Appetite

If you are pumping 25 ounces a milk a day, you are burning the same amount of extra calories as if you were running 5 miles every single day. You are going to be hungry!

Two things that I have done to combat this – first, make sure that you are eating enough calories. If you would normally eat, say, 1500 calories to lose weight, figure out how many breastfeeding calories you are burning and add that to the total that you eat every day. The second is to have a lot of easy, weight-loss friendly snacks on hand that work for you. My usual snack is a few spoonfuls of an enormous fruit salad that I make at the beginning of every week along with a Hershey’s Kiss. Between the bulk of the fruit and the fat from the Kiss, it’s reasonably filling.

Challenge #3: Sleep Deprivation

For years, studies have shown a link between weight gain and sleep deprivation, so the advice that doctors and weight loss gurus give people trying to lose weight is to sleep for eight consecutive hours a night. When you have a new baby, that’s obviously just not going to happen. (Unless you are really lucky!)

When you baby gets a little older, though, hopefully it will – and then getting a good night’s sleep is great advice to follow. Before that, though, what to do?

The issue with sleep and weight gain is that lack of sleep makes your body want more food. Junk food, to be specific. The good news is that, if you don’t give into the impulse to eat lots of high-calorie food, you will probably be fine – the lack of sleep on its own doesn’t seem to affect the calories in/calories out equation. However, if this is really hard for you, maybe just recognize that weight loss might be too difficult when you aren’t sleeping well and wait to start trying to lose weight until your baby is sleeping longer stretches.

Challenge #4: You Have a Baby and No Longer Have Any Free Time

It’s hard to get time to yourself when you are a new mama to a baby. I find this to be a weight loss challenge for two reasons. The obvious one is that you have less time to work out, which I’ll talk about in the next post.

The less obvious one, though, is that when you find yourself stressed, it’s harder to deal with it in the ways you might have pre-baby (taking a walk, taking a bath, going out with your friends) because you have an infant. It’s much easier to just eat something and feel better. (I have a lot of experience in eating my feelings – I think I have an extra stretch mark for every ultrasound I went to when I was pregnant with my son!) For me, the first step to dealing with this is recognizing what I’m doing. From there, you can come up with a plan that works for you to try not to eat due to stress.

Want more information about losing weight while breastfeeding? You can read about exercising and breastfeeding here and my experience with losing weight while breastfeeding here.

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