Dear Coach: Does Exercise Affect Milk Supply?

My wife is worried that exercise – especially training with weights – will interfere with breastfeeding. Will exercise decrease her milk supply?

Dear Coach,

My wife gave birth to our second son at the end of August. We are very happy and proud to have two children as a part of our family. However, my wife has been feeling very self-conscious this time around as her body isn’t getting back to her pre-pregnancy shape as quickly as the first time. I asked her if she was interested in learning how to use a kettlebell and she said yes! I have started teaching her the swing, and the Turkish get up, and things are going pretty well.

However, the other day when we got the kids to sleep I wanted to have another training session with her. She told me she was worried that working out, especially with weights, might affect her milk supply negatively. I’ve Googled, and read and read, and there is so much conflicting information on the web that it is hard to know what to believe. Will exercise affect my wife’s milk supply?


Concerned Husband

Dear Concerned Husband,

I think it’s awesome you are supporting your wife the way you are, both in terms of the training and in seeking out the facts about postpartum exercise. You are right – there is a lot of conflicting information out there and it’s hard sometimes to sort it all out! Let me tell you what I know about lactation and exercise, both from a factual perspective and my own experience.

The studies done on exercise and lactation seem to suggest that regular, moderate to high-intensity exercise does not affect milk supply. The misconception that exercise does decrease milk supply actually goes way back to a study from the 1970s, in which increases in physical activity were shown to decrease milk production in cows. When you think about a cow’s normal activity level compared to the average human being’s, you can see why this study isn’t exactly relevant. I can personally vouch that if your wife has two young children, she’s probably more active than the average cow grazing in the field.

A few decades later, another study showed that high-intensity workouts (i.e., exercise sessions that exceed the woman’s anaerobic threshold) can alter the taste of human milk, due to increases in lactic acid. It doesn’t sound to me like this is what your wife is doing, but even if it was, it’s important to note that even these conditions do not decrease supply or even affect milk quality. Very high-intensity exercise may alter the taste of human milk and some infants might not like that. Fast forward to 2012, and you will find a meta-analysis in Pediatrics journal confirming that exercise does not affect infant growth, which is the real issue at stake in decreased milk supply.

As an active mom myself, I can say that exercise has never seemed to affect my milk supply. The key is to allow plenty of time in those first weeks after birth to establish a good supply with frequent nursing, lots of skin-to-skin contact, and pumping if necessary. I can think of a few times after a long run or intense workout that my daughter didn’t want to nurse right when I came home. However, I don’t think that this had to do with the taste as much as it did my own elevated heart rate and sweaty workout clothes. Babies like to feel secure and calm when they nurse. My experience was always that if mom is stressed or excited, they know. For this reason, I would advise that your wife always breastfeed before her workout.

If your wife still feels like she is having problems maintaining her milk supply, discuss it with her doctor or a lactation consultant, since there may be other factors at work. However, most studies show that as long as mom is nursing frequently, eating a healthy and balanced diet, and drinking plenty of water, she’s probably making more than enough milk to support her baby’s growth.

Moms and dads have so many questions on their mind and it can be frustrating when the answers conflict with each other. I hope this information is helpful, and congratulations to you and your wife on your new addition!

Coach Nicole Crawford

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