Returning to physical activity after childbirth often comes with anxiety about maintaining a sufficient milk supply. The perception that exercise might negatively affect lactation can create a barrier to resuming fitness routines. Understanding the biological relationship between physical activity and milk production is important for safely integrating exercise back into a postpartum lifestyle. Scientific evidence indicates that, under most circumstances, physical exertion does not compromise a parent’s ability to nourish their infant. This article explores how exercise affects milk volume and composition, and provides practical steps for managing an active lifestyle while breastfeeding.
Exercise and Milk Volume
Moderate physical activity does not decrease the overall volume of milk produced. Studies involving lactating individuals engaging in aerobic exercise have shown no long-term reduction in milk supply or adverse effects on infant weight gain. Milk production is primarily regulated by the hormones Prolactin, which signals the body to make milk, and Oxytocin, which triggers the milk ejection reflex. Moderate exercise does not significantly lower Prolactin levels or interfere with Oxytocin release, allowing the milk-making process to continue normally.
Concerns about milk volume are usually not related to the activity itself but rather to insufficient fuel intake or dehydration. Lactation requires a substantial energy expenditure, generally demanding an additional 300 to 600 calories per day. When a person attempts to lose weight too rapidly or restricts calories severely, the resulting energy deficit can threaten milk supply. A severe energy deficit may cause the body to prioritize conserving energy over milk synthesis, potentially leading to a drop in volume. Gradual weight loss (0.5 to 1.5 pounds per week) is generally considered safe and does not affect milk volume or composition when coupled with adequate nourishment.
High Intensity and Lactic Acid
While the quantity of milk remains stable with moderate activity, high-intensity exercise can temporarily alter the milk’s flavor. Strenuous activity that pushes the body past its anaerobic threshold causes a build-up of lactic acid in the bloodstream. This temporary increase in lactic acid then transfers into the breast milk.
The elevated lactic acid concentration may give the milk a slightly sour or salty taste. This flavor change is not harmful to the infant, but it has been noted in some early studies to cause temporary refusal or fussiness immediately following a maximal workout. Maximal exercise is activity intense enough to reach maximum oxygen uptake.
For most individuals, the increase in lactic acid is short-lived, with levels returning to normal within 30 to 60 minutes after the intense session ends. Infants accepted milk expressed one hour after maximal exercise without issue, despite a small increase in lactic acid levels. Moderate exercise, such as a brisk walk or light jog, does not typically lead to a noticeable increase in lactic acid in the milk.
Practical Guidelines for Breastfeeding Athletes
Calorie and Energy Intake
Maintaining adequate energy intake is paramount for supporting both physical activity and the energy demands of lactation. Breastfeeding parents need to consume calories sufficient for their basal metabolic rate, the additional energy for milk production, and the calories burned during exercise. Experts advise against consuming fewer than 1,500 to 1,800 calories per day, with many requiring the higher end of this range or more. Consistent fueling throughout the day, including planned snacks, helps prevent the body from entering a severe energy deficit that could impact supply.
Hydration
Fluid intake is another important factor, as dehydration can quickly affect milk volume. Breastfeeding requires a significant amount of water, and sweating during exercise increases this need further. A general guideline is to consume 8 to 12 ounces of fluid for every 45 minutes of moderate exercise. Incorporating electrolyte-containing beverages can be beneficial to replace minerals lost through sweat, especially during prolonged or high-heat workouts.
Timing Feeds
Timing of feeds or pumps around exercise can help manage comfort and potential taste changes. It is often recommended to feed or express milk immediately before a workout to reduce breast fullness. Exercising with full breasts can be uncomfortable and may increase the risk of blocked ducts. If a workout is particularly intense, waiting about an hour after completion before feeding can allow time for any temporary lactic acid elevation to subside.
Supportive Gear
Wearing a properly fitted, supportive sports bra is also a practical consideration for comfort and breast health. A bra that is too restrictive or tight may put excessive pressure on the milk ducts, which could potentially lead to blockages. Choosing one designed for high impact, with adequate compression but without rigid underwire, can help ensure comfort and prevent potential issues during exercise.