The Inside Scoop on Breastfeeding and Exercise

Balancing breastfeeding and working out can, to say the least, be a logistical challenge. So we turned to an expert for the lowdown on how the two can peacefully co-exist. Dr. Alison Stuebe, assistant professor in the division of maternal and fetal medicine at the University of North Carolina School of Medicine, debunked some common myths and shared her fascinating Sir Mix-a-Lot theory of breastfeeding (hint: it has something to do with your booty). Bonus: We also scored four practical tips from New York–based lactation consultant Quetzal Currie. Read on to find out how you can nurse and still hit the gym like you mean it.

A:There’s some evidence that high-intensity exercise can increase lactic acid levels in milk in the first 30 to 60 minutes after feeding. However, that doesn’t seem to matter to babies. In one study, mothers expressed milk before and after exercising and babies were video taped drinking their mom’s “before” and “after” milk from a familiar bottle. After maximal exertion, levels of lactic acid were slightly higher, but the babies had no complaints. Other studies have found that moderate exercise doesn’t affect levels of immune factors in mothers’ milk. If a baby is fussy nursing right after mom’s workout, it may be that the breast is salty from sweat, rather than because of any change in milk composition.

A: It depends. Moms need calories to maintain their baseline energy needs; make milk, which takes about 500 calories a day; and support exercise. Those calories come from the food they eat and from fat that’s stored during pregnancy to use to feed the baby during breastfeeding. There is research showing that it’s safe for mothers to exercise, cut calories and lose up to a pound a week while breastfeeding. We don’t have data about the effects of losing weight faster than one pound per week, so moms who are exercising intensively may need to eat more, or check in with their pediatric provider to see that their baby is gaining appropriately.

A: We know that breastfeeding affects a woman’s fertility. In the first six months after birth, exclusively breastfeeding women who have not yet gotten their period have a very low risk of pregnancy. By suppressing a woman’s menstrual cycles, breastfeeding lowers levels of estrogen and progesterone. We also know that when breastfeeding women use stored fat, their bodies preferentially go to the fat on a woman’s hips and thighs. It’s thought that fat in this area is higher in omega-3 fatty acids that are important for baby’s brain development. In fact, one team of researchers suggested that men are attracted to women with ample hip and thigh fat because it suggests a bigger supply of brainpower for their future children—which I refer to as the Sir Mix-a-Lot theory of big butts and breastfeeding.

A: There is some interesting work on how lactation affects women’s physiology when they are exercising. During a treadmill test, lactating women had lower levels of stress hormones than non-lactating women, though it’s not clear how that might translate into training results.

A: There are lots of factors that are associated with changes in milk supply. The most common cause is reduced demand. After the first few weeks, breasts make as much milk as the baby or breast pump removes, relying on negative feedback from full breasts to adjust production. If there’s less milk being consumed, the breasts produce less. Frequency matters: Although some moms can go five or six hours between feedings and then produce gobs of milk, most breasts start to shut down production if they are persistently full to over-full. Feeding every few hours is not how our breasts evolved. Our ancestors carried their babies in slings and breastfed continuously. My clinical hunch is that many women who struggle with supply might do fine if they were able to wear their babies and feed every one to two hours. Unfortunately for moms who need to return to work, that’s often not feasible.

A: For moms who are training, it’s probably wise to nurse right before a workout session. That will protect your supply and it will also be a lot more comfortable. For endurance training, that might also mean scheduling a break to feed or express milk during a long workout.

A: On a population level, the evidence suggests that women who breastfeed longer and more intensely lose more weight than women who breastfeed less. That’s likely due to the 500 calories a day required to make milk. Anecdotally, some mothers describe not being able to lose weight until their babies are weaned. This may be part of our evolutionary heritage: For most of our history, food was scarce and lactating women had to provide enough energy for two people. It would make sense for her body to conserve calories and some women may have a more active conservation mechanism than others.

A: For the individual woman, weight loss during breastfeeding is ultimately about calories out versus calories in. You can burn 500 calories breastfeeding or running for four miles, but if you eat an extra 500 calories, neither breastfeeding nor running will help you to lose weight.

Tips and Tricks

Lactation consultant Quetzal Currie shares four tips for making nursing and fitness work together.

Stay hydrated. Drinking to thirst is usually sufficient. The baby will get what he or she needs even if you don’t drink enough, but you’ll end up dehydrated if you ignore signs of thirst. Have water near by so it’s easily accessible.

Prioritize your bra. Wear a supportive bra, but make sure it’s the right size. Your breasts are likely to be larger now, so squeezing into a bra that’s too small can cut into you and increase your chance for clogged ducts.

Timing is everything.Nurse or pump right before your workout if possible to avoid engorgement or leaking.

Keep things clean. You may want to shower or wipe your breast with water and a washcloth before nursing if your baby is rejecting your breast. It may be because your skin is salty.

For more tips on how to breastfeed while training, read our interview with accomplished runner and mom of two Michele Gonzalez, aka NYC Running Mama, here.