Breastfeeding and Exercise

After I had my son and began running again, I had several well-meaning friends and friends of friends warn me that running would deplete my milk supply. As a first-time mom, I was terrified of my milk supply depleting, so I took to the medical journals for information. Before I launch into the science of exercise and breastfeeding and how the two are actually quite complementary, let me reassure you. I ran 4-7 miles 3-5 times per week (and even raced) while breastfeeding, and breastfed my son until he self-weaned at 19 months. And it’s not just me – don’t worry. Research shows (repeatedly, in many studies) that exercise and breastfeeding are actually complementary.


Before reading any further:

If any of the following apply to you, be sure to ask your doctor or lactation consultant specifically about exercising while breastfeeding, because the information I’m about to share with you from the research may not apply in your situation:

  • Your baby has any kind of special needs
  • You think that you may need to go on a special diet to help you lose your pregnancy weight for health reasons
  • You have a low BMI of less than 18.5
  • You plan to restrict your diet to lose weight post-pregnancy (consuming less than 1500-1800 calories per day)
  • You have struggled with nutrition and weight loss or gain in the past
  • Your baby is not gaining weight as he or she should
  • You are planning to train for any form of athletic competition during breastfeeding
  • You have questions about how your diet and exercise plan could affect your baby’s growth and development

Extra calories needed:

Research shows that your body requires an extra 500-650 calories per day while breastfeeding.1,2 So if you’re exercising, factor the extra calories your burning while exercising in addition to the extra 500-650 calories you already need.

Milk Quality and Quantity:

Consistently, research shows that regular exercise does not have a negative effect on the quality, nutrient composition, or quantity of breast milk you produce.2-5 In fact, research shows that moms who exercise actually produce slightly more milk (slightly higher volume, but not statistically significant) than non-exercising moms.2 How is that possible? Your breast milk will have similar characteristics with your body composition. If your body has more fat, so will your milk. Fat has more calories per ounce, so if your milk is leaner, you’ll have to produce slightly more in volume to achieve the same amount of calories as someone making milk with higher fat content.6 It’s kind of like chocolate cake vs. angel food cake. You’d have to eat lots and lots of angel food cake to match the calorie content of one slice of chocolate cake.

Lactic Acid:

If you’re worried about the taste of lactic acid in your milk, there have actually been baby taste tests to compare regular breast milk with breast milk plus lactic acid (immediately after exercise)! It turns out some babies in one study cared more about whether they were fed with an eye dropper than whether the lactic acid was present, and some felt the milk was less palatable in the first 10-30 minutes after exercise.3,7

Formula feeding vs. breastfeeding – comparing the effect on weight loss:

Your body will create a natural buffer during the first 3 months if you’re breastfeeding to protect your baby’s food supply. You may get frustrated if your initial weight loss from the baby’s birth plateau’s for 3 months, but know that’s your body’s natural way to guard your baby’s food supply, especially in the event of a famine. Several studies have compared weight loss among exclusive breastfeeding moms, combination (formula and breastfeeding) feeding moms, and formula-only feeding moms. By 6 months, women who have exclusively breastfed will have lost the most weight, followed by moms who combination-fed (some breast milk, some formula) and the exclusive formula feeders will have lost the least weight.1,4,6 By the 1 year mark, moms who are still breastfeeding are more likely than formula feeding moms to be back to their pre-pregnancy weight, and moms who are formula feeding at the 1 year mark tend to be about 4% above their pre-pregnancy weight at their baby’s second birthday party.6

Weight loss in the first year while breastfeeding:

Every body, every woman, every pregnancy, and every baby is different. Some women actually gain weight while breastfeeding.1 Research has some averages for us, for reference, though. Taking the population as a whole, breastfeeding moms who aren’t consciously dieting will lose about 0.44-1.77 pounds per month during the first 6 months and 0.22-0.44 pounds per month in the second 6 months (6 months is when solid food is typically introduced), with a surge in weight loss that occurs somewhere between 9 and 12 months when your baby becomes more mobile.6

Diet + Exercise + Breastfeeding?

If you’re considering dieting while breastfeeding, you must discuss it with your physician and a lactation consultant. For reference, one research study showed that overweight women who exercised 4 times per week for 45 minutes and consumed 1800 or more calories per day did not have any negative effects on milk supply.5

How it All Works:

Research from around the world shows that your body has a very organized process for making sure you have enough milk for your baby. It’s easiest to get a feel for how this works by looking into cultures where there aren’t a whole lot of energy intake/output variables. Often those cultures are subsistence farming communities, where everybody works so that nobody goes hungry. They don’t have surplus food to sell. Without extra variables like grocery stores or gyms, they are great for researchers to get down to the nitty gritty of the calorie consumption and energy output of breastfeeding moms.6,8,9


When you’re breastfeeding, you’ve got to have extra calories to make milk. That can basically either happen by consuming more food or expending less energy (doing less). On the whole, women tend to do a bit of both. Research shows 56% of the extra calories needed for breastfeeding come from eating more, and 44% come from doing less, with an overall net burn of body mass in the process.6 Here’s how your body makes that work:6


firstStep 1: Make mom hungrier so she’ll consume enough calories to make milk.

Have you noticed that you eat like a health-conscious 16 year old boy? That’s what’s going on there. Your increased appetite while breastfeeding is your body’s first way to get you to meet the caloric demands of making milk.

secondStep 2: Use mom’s fat stores.

If mom isn’t able to get more food, burn the furniture.

thirdStep 3: If mom isn’t able to eat more or isn’t listening and we’re out of fat stores, make mom do less.

If step 1 and step 2 won’t work or can’t work (like if you are in a subsistence farming community and can’t get more at the grocery store, and you don’t have much by way of fat stores), you may feel lethargic or naturally do less throughout the day, and this response would be amplified for exercising moms. Breastfeeding moms in subsistence farming communities actually take on more sedentary tasks for the community while they’re breastfeeding.

fourthStep 4: If steps 1-3 haven’t yielded enough extra calories to make enough milk, make mom more efficient in her movements.

This is likely the same process your body used while pregnant. Your body is actually able to get more calories out of a turkey sandwich while you’re pregnant compared to the same turkey sandwich eaten by non-pregnant you.10 Pretty amazing, right?


1. Lovelady C. Balancing exercise and food intake with lactation to promote post-partum weight loss. Proceedings of the Nutrition Society. 2011;70(02):181-184.
2. Dewey KG. Effects of maternal caloric restriction and exercise during lactation. The Journal of Nutrition. 1998;128(2S):S386.
3. Meyer DL. Effect of Postpartum Exercise on Mothers and their Offspring: A Review of the Literature. Obesity research. 2002;10(8):841-853.
4. Adegboye AA, Linne YM. Diet or exercise, or both, for weight reduction in women after childbirth. Cochrane Database of Systematic Reviews. 2013;(7):1-67.
5. Lovelady CA, Garner KE, Moreno KL. The effect of weight loss in overweight, lactating women on the growth of their infants. New England Journal of Medicine. 2000;342(7):449-453.
6. Lederman SA. Influence of lactation on body weight regulation. Nutrition reviews. 2004;62(7):S112-S119.
7. Dewey KG, Lovelady CA. A randomized study of the effects of aerobic exercise by lactating women on breast-milk volume and composition. New England Journal of Medicine. 1994;330(7):449-453.
8. Adair LS, Popkin BM. Prolonged lactation contributes to depletion of maternal energy reserves in Filipino women. The Journal of Nutrition. 1992;122(8):1643-1655.
9. Panter-Brick C. Seasonality of energy expenditure during pregnancy and lactation for rural Nepali women. The American Journal of Clinical Nutrition. 1993;57:620-628.
10. Abeysekera MV, Morris JA, Davis GK, O’Sullivan AJ. Alterations in energy homeostasis to favour adipose tissue gain: A longitudinal study in healthy pregnant women. Australian and New Zealand Journal of Obstetrics and Gynaecology. 2016;56(1):42-48. doi:10.1111/ajo.12398.