The Effect of Exercise on Breastmilk
by Anne Eglash MD, IBCLC, FABM
Exercise is obviously important for all of us, and many women look forward to getting back into previous exercise routines after giving birth. In fact, the US Centers for Disease Control recommends that pregnant and postpartum women engage in at least 150 minutes of moderate-intensity aerobic exercise spread throughout each week.
Many mothers wonder if exercise will drop their breastmilk supply, and whether exercise changes the taste or quality of their breastmilk.
The authors of this week’s article sought to test whether moderate or high intensity physical activity affected certain nutrients in breastmilk and the volume of breastmilk.
The authors recruited 31 women who were exclusively breastfeeding their 2-6 month old infants. Each mother expressed their breastmilk before moderate exercise and 1 hour after. On another day, the same mothers expressed their breastmilk before rest and 1 hour after. Therefore, each mother was her own control.
The mothers kept a similar diet and fluid intake on each day. The milk samples were analyzed for protein, fat, lactose, calories, and volume. The authors found no differences in the breastmilk quality or volume after exercise as compared to after resting.
- High intensity exercise in 1 study was found to increase lactic acid in breastmilk.
- Studies consistently have shown no impact of maternal exercise on infant weight gain.
- Sodium content is lower in breastmilk after exercise because the mother loses salt in her sweat.
- Calcium levels in breastmilk were found to be lower in breastmilk after exercise, because of the demand for calcium in the bones of exercising mothers.
See the Answer
There are multiple health benefits associated with both breastfeeding and practicing physical activity (PA). Therefore, it is likely that many women might want to engage in both. We designed the current randomized clinical trial to examine the effect of moderate- to high-intensity PA on human milk (HM) volume and macronutrient contents.
Methods and Study Design
In this prospective, randomized, crossover clinical trial, we recruited 31 healthy mothers who had been exclusively breastfeeding their infants. Mothers expressed HM twice each day on 2 consecutive days—a day with PA (1-hour before and 1-hour after PA) and a control day without PA (at the exact same hours of the day). The order of days (with/without PA) was determined randomly. Macronutrients and energy contents of HM were analyzed using the Human Milk Analyzer (Miris AB, Uppsala, Sweden). PA was graded according to the Borg Rating of Perceived Exertion scale (RPE scale).
A total 124 HM samples from 31 mothers were analyzed. Moderate- to high-intensity PA affected neither macronutrients (fat, carbohydrates, protein) nor energy content. Milk volume remained unaffected by PA as well.
Maternal PA does not affect HM volume or its macronutrient contents. Lactating mothers can be reassured regarding their breast milk volume and composition while practicing PA of moderate to high intensity.
There has been at least 1 study showing an increase in lactic acid in breastmilk after intense exercise but there was no change in the pH (acidity) of the milk. A few studies have shown no negative effects on infant weight gain with exercise during breastfeeding. I was just kidding about sodium and calcium being lower in breastmilk due to exercise. Studies have shown that electrolytes (sodium, potassium) and calcium remain stable after exercise.
I receive questions about the safety of exercise during breastfeeding fairly often in my practice, and I think there has been sufficient evidence published to say that exercise does not negatively impact breastmilk. Breastfeeding mothers also ask about the safety of weight loss during breastfeeding. There is very little research on the maximum amount of weight loss per week or month that would be safe, to prevent a drop in milk supply.