Exercise: Does it cause a reduction in milk supply?

I am nursing my six-month-old daughter. I am 40 pounds overweight and I have joined a gym for some moderate exercise. I have found that after a week of exercise, my milk supply has decreased a great deal. How can I lose weight through exercise while keeping up my milk supply?

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Debbi Donovan

Debbi Donovan is a Board Certified Lactation Consultant, as well as a retired La Leche League Leader. For more than a decade, Debbi... Read more

Congratulations on starting a healthy program of diet and exercise! I am not aware of any research indicating that exercise can cause a permanent reduction in milk supply. To the contrary, several studies confirm that aerobic exercise does not have a negative affect on lactation.

"Aerobic exercise performed four or five times per week beginning six to eight weeks postpartum had no adverse effect on lactation and significantly improved the cardiovascular fitness of the mothers." (N Engl J Med 1994 Feb 17;330(7):449-453)

"Exercise sufficient to improve cardiovascular fitness without substantially altering energy balance does not adversely affect lactation performance." (Nutr Rev 1994 Oct;52(10):358-360)

"Aerobic exercise improves cardiovascular fitness and does not affect milk energy transfer to the infant." (J Nutr 1998 Feb;128(2 Suppl):386S-389S)

"Exercising subjects tended to have higher milk volume (839 vs 776 g/d) and energy output in milk (538 vs 494 kcal/d). Thus, there was no apparent adverse effect of vigorous exercise on lactation performance." (Am J Clin Nutr 1990 Jul;52(1):103-109)

Perhaps there are other circumstances that are causing a reduction in your supply at this time and confusing the issue.

Around the age of six months many babies begin eating solid foods. Have you added solids to your daughter's diet? If so, she may be nursing less often. This, of course, will cause a decrease in your milk supply. It is important to remember that breastmilk is the priority during your baby's first year of life. Breastfeed before offering your little one small amounts of solid foods.

Perhaps your baby is fussy at the breast and you are interpreting this as a reduced milk supply. Some babies may seem irritable at the breast when nursed immediately following vigorous exercise, though this is not always the case. It has been found that lactic acid levels in breastmilk may increase following 30 minutes of aerobic activity, giving a bitter, sour taste to the normally sweet breastmilk. If your baby seems unhappy at your breast following exercise, nurse immediately prior to working out, wait an hour after exercise to breastfeed, express a bit of milk before offering your baby the breast, and gently rinse any perspiration from your breasts.

In many cultures -- both past and present -- nursing moms would get plenty of exercise as part of their daily work/activities. It is doubtful that they experienced milk supply reduction or it could have resulted in dire consequences, as mothers' milk was often the sole form of nutrition. I have no doubt that a woman's body, though often unaccustomed to vigorous activity on a daily basis, can supply her baby with all the nutrition he or she needs while she continues a program of moderate exercise. My best wishes in mothering!

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