Breastfeeding and Exercise

As a Lactation Consultant I get asked all kinds of breastfeeding related questions. I would have to say the one question that comes up most frequently relates to breastfeeding and exercise. Most new mother’s can hardly wait to get back to the gym once their Doctor has given them the thumbs up at their 6 week post-partum check-up. As women we naturally put (unnecessary) pressure on ourselves to get back into our pre-baby skinny jeans as fast as humanly possible. I am too guilty of this phenomenon.  With all 3 of my daughters I’m pretty sure (but can’t remember 100%) that I started going back to the gym or running even before I got the ok from my Obstetrician. I knew that breastfeeding was helping to shed a LOT of those pounds gained during pregnancy by keeping my metabolism revved up........ but I wanted to help it out a little more!! The average woman burns an additional 300-500 calories/day just by producing breastmilk for her baby. That’s like doing half a spin class....without actually having to get on a bike!!!  

But what are the effects of exercise on breastmilk? Does exercise affect your milk supply? Does exercising change the taste of your breastmilk? These are some of the questions this blog will answer.

It has been widely researched and documented that moderate exercise while breastfeeding improves your health in a variety of ways. Exercise has positive effects on your emotional well-being thanks to all those lovely endorphins that circulate through your system while your heart rate increases. Breastfeeding women have improved lipid profiles and better insulin response while exercising. Women report feeling less stressed, have an enhanced maternal infant relationship, and if they are having symptoms of post-partum depression, those symptoms are often alleviated with exercise.

So does exercising while breastfeeding impact ones milk supply? I have worked with a number of clients who felt that once they returned to the gym, their supply went down. Research shows that moderate exercise, and by moderate, I mean not pushing yourself to 100% exhaustion, has no negative effect on milk supply, milk composition, or baby’s growth.

Based on the numerous studies I have read, I believe it is not exercise itself that effects supply, but perhaps the ‘taste’ of the milk is altered slightly due to a metabolic bi-product of exercising called Lactic Acid. Perhaps it is this altered taste of the breastmilk that bothers the baby and prevents proper drainage of the breast, which over time, could lead to a decrease in milk supply. My theory would only hold true for those breastfeeding women who are pushing themselves to exhaustion while exercising. If you fall into the moderately exercising category, the lactic-acid build-up is not enough to alter the taste of your milk.  I am not a researcher by any stretch of the imagination. I am merely hypothesizing based on my own personal observations of clients who have noticed a decrease in their supply after resuming ‘vigorous’ exercise. Most of the literature does not support my observations but I don’t think it is fair to rule out lactic acid as a contributing factor to changes in breastfeeding patterns if mom has recently started exercising again.

Now let’s take a closer look at what the literature tells us:

There have been a couple of studies over the years related to the presence of Lactic Acid in breastmilk post-exercise. Research has not shown a noticeable increase in lactic-acid build-up after moderate exercise (50%-75%) intensity. BUT, the Lactic acid in breastmilk does increase somewhat if the mother exercises to maximum (100%) intensity, also described as exhaustive exercise. I don’t know about you, but I’m pretty sure those first few months back at the gym, I was feeling pretty exhausted after my work-outs. I couldn’t run the same distances, my core was a total mess, and my overall ‘strength’ was practically non-existent. I know I pushed myself pretty hard and probably had a fair bit of lactic acid build-up in my milk. I was also blessed (and sometimes cursed) with an abundant milk supply. So I’m sure that’s what saved my supply from decreasing, but I do remember times when my girls refused to breastfeed after I returned home from the gym or from a run. I’m pretty sure it was the lactic acid altering the taste of my milk that my girls were not fond of.  Lactic acid may be present in the breastmilk for up to 90 minutes post-exercise but there are no known harmful effects for the baby.

So does this mean that your baby will refuse to breastfeed after a vigorous work-out?  Most studies have found no difference in acceptance of the breast even after a maximum intensity work-out. There was a highly publicized study in 1992 that indicated a baby might fuss or refuse expressed milk from a mom who had been exercising at 100% intensity. The results of this study were questionable because these breastfed babies were actually fed breastmilk from a medicine dropper. No wonder they acted strangely when being fed their mother’s breastmilk...they were being fed in an unfamiliar way. In addition, these mothers reported that the babies had not had any feeding problems post-exercise to begin with. A more recent study showed no change in infants’ acceptance of mom’s milk an hour after exercise, even for the moms who exercised at a maximum intensity (and did have a slight increase in lactic acid in their milk. Bottom line is, it is safe to breastfeed even after a vigorous work-out. The milk may be slightly altered in taste but MOST babies will not refuse the breast.

If your baby is one of those few who refuses the breast after you get home from the gym, it could be for a variety of other reasons. Most likely when you get home from your work-out, you are going to be a sweaty hot mess (I know I always was...and still am today when I workout). If you decide to feed your baby before you have a shower or wipe off your breasts, there is a good chance your little one will refuse to breastfeed because you taste salty...and probably smell a little different too.  So remember to have a quick rinse before you decide to latch baby on!!! But if your baby consistently refuses to breastfeed after you exercise, he may be a bit more sensitive to the taste of lactic acid in the milk. Don’t worry about this....lactic acid in the breastmilk is safe for your baby to consume. Nothing bad is going to happen!!

You could consider doing the following:

  • Express 10-15mls of milk from each breast before feeding baby
  • Delay feeding baby for 30 minutes or so to allow lactic acid levels to subside
  • And/or try decreasing workout intensity levels.....try being the optimal word here

Some other suggestions for when you resume your work-out regime are the following:

  • Pump or breastfeed the baby right before you exercise
  • Wear a good, supportive bra (with no underwire) while exercising
  • If you regularly lift heavy weights or do other exercises involving repetitive arm movements (Tracy Anderson Method) you may be more at risk for developing plugged ducts
  • Keep well hydrated before, during, and after you exercise!!!!

So how about the effect of exercise on immunologic factors in breastmilk? The immune factor that gets mentioned the most when it comes to exercise and breastmilk is IgA.  Basically, immune factors protect a baby from becoming ill.  IgA is the antibody that protects our mucous membranes from being infiltrated by bacteria and viruses. It is the most common antibody found in breastmilk. A few small studies have shown that there is no difference in immunologic factors after moderate exercise, but that IgA levels are decreased short-term after exhaustive exercise. ‘Most’ breastfeeding mothers do not exercise to exhaustion, but for those that do so and breastfeed soon after, a decrease in IgA levels in one feeding per day are unlikely to be significant.

In 1997, a study by Gregory et al found that IgA levels in breastmilk were decreased for a short period of time (10-30 minutes) after mom had exercised strenuously, but that levels had returned to normal within an hour. They also observed that IgA levels increased after the breast had been emptied, whether or not mom had been exercising strenuously. In 2003, Lovelady et al looked at immunologic factors (IgA, lactoferrin, lysozyme) in breastmilk after moderate exercise and found no difference in the milk of exercising and non-exercising mothers. So there you have it, straight from the experts..... going to the gym and getting your sweat on is not going to alter the important immunologic components of your precious milk!!!!

I think that about sums it up. I hope the information shared was helpful and informative. As always, please feel free to contact me with any questions, concerns, or comments. Happy Breastfeeding and Happy Exercising!!!!


 Leanne Rzepa RN BN IBCLC


Posted on December 16, 2015 .