Can Exercise and Dieting Affect Your Milk Supply? A Compassionate, Evidence-Based Look

CW: This article discusses body image, weight loss, and restrictive eating.

If you're in the postpartum phase and breastfeeding, you're juggling a lot—feeding schedules, sleep deprivation, hormonal shifts, and maybe even a changing relationship with your body. In the midst of all this, you might be wondering: Can I safely return to exercise? Will dieting help me lose the baby weight? Could any of this affect my milk supply?

Let’s unpack all of that in a way that supports your health, your goals, and your breastfeeding journey—with no shame, just evidence and empathy.

Lactation is biologically brilliant—and metabolically demanding. Producing breast milk takes an estimated 450–500 extra calories per day ⁽¹⁾ . That’s about the same energy expenditure as a 5-mile run or an intense hour-long cycling session, and that’s nearly 20% more than pregnancy.

Lactation is biologically brilliant—and metabolically demanding. Producing breast milk takes an estimated 450–500 extra calories per day ⁽¹⁾ . That’s about the same energy burn as a 5-mile run or an intense hour-long cycling session—nearly 20% more energy than pregnancy requires.

To consistently support milk production, your body needs a steady supply of calories, macronutrients (carbs, fats, and protein), and hydration . When any of those are in short supply—especially after intense exercise—your body may shift into energy-conservation mode , prioritizing your survival and recovery over milk output ⁽²⁾ .

If you’re noticing a dip in your supply after resuming or increasing physical activity, you’re not alone—and the causes are multifactorial. Here's what's going on under the surface:

Milk production is a hormonally driven, energy-dependent process. When your body detects a caloric deficit —which can happen when exercise is added without increasing food intake—it shifts resources away from "non-essential" systems to maintain homeostasis. Since lactation is technically non-essential to maternal survival , your body may reduce milk volume in response to unmet energy needs ⁽⁴⁾. This is especially true if you’re:

• Eating less than your body requires for both recovery and lactation

• Skipping meals or snacks post-workout

• Exercising in a fasted state or under-fueling consistently

A helpful analogy: If you're not fueling the fire, the heat (milk production) starts to dwindle.

During intense or prolonged exercise, your muscles rely on glycogen stores —the body’s carbohydrate reserve. Once glycogen is depleted, cortisol , your body’s stress hormone, increases to help mobilize energy from other sources (like fat and protein). This elevated cortisol can interfere with prolactin and oxytocin , the two key hormones responsible for milk production and letdown ⁽⁵⁾ .

• Prolactin stimulates milk production

• Oxytocin helps with milk ejection (letdown reflex)

If cortisol is elevated post-workout and you’re not replenishing those glycogen stores with carbs, you may find that your letdown is sluggish or your baby seems less satisfied after nursing.

Even mild dehydration can impact plasma volume (the fluid portion of your blood), which in turn affects milk volume ⁽⁶⁾ . Sweat loss from vigorous exercise, especially without proper rehydration, can lead to a temporary dip in supply. This is particularly relevant if you're nursing and sweating heavily in warmer weather, or if you're exercising intensely without increasing your fluid and electrolyte intake ⁽⁶⁾ .

Pro tip: Aim for at least 16–20 oz of water after each workout, and consider adding a pinch of sea salt or She’s Thirsty to help with fluid retention and muscle recovery.

Lactating parents need more protein to support breast tissue regeneration, hormone production , and milk composition. ⁽⁷⁾ If your post-exercise diet is low in protein or essential fatty acids, your body may not have enough raw materials to maintain adequate milk output. Essential fats like DHA (found in foods like salmon, eggs, or algae oil) are especially important for both maternal recovery and baby’s brain development. ⁽⁸⁾

Exercise is a form of stress—even when it's healthy. And while moderate movement supports mental health, circulation, and blood sugar balance , intense or prolonged physical stress can signal to your nervous system that energy is scarce. This sympathetic activation can reduce milk ejection reflexes and make nursing feel less productive or more frustrating for both you and baby.

To support consistent milk production, your body needs adequate calories, macronutrients (carbs, fats, and protein), and hydration . Without them, your body may compensate by dialing back milk supply to protect your own energy balance ⁽²⁾ .

And it’s not just about calories— micronutrient needs are also heightened during lactation. Key nutrients like iodine, choline, B vitamins, vitamin A, and DHA play a crucial role in supporting both your recovery and your baby’s development through breast milk ⁽²⁾⁽³⁾ .

Because these increased demands can be hard to meet through food alone—especially in the busy, sleep-deprived postpartum season— continuing a high-quality prenatal or postnatal vitamin is highly recommended. Products like Legendairy Milk's Dynamic Duo are specially formulated to fill those nutrient gaps, supporting your energy, recovery, and milk-making needs during this phase.

We’ve all heard the claim: Breastfeeding melts the baby weight right off! But the reality is more nuanced.

Breastfeeding can support gradual, healthy postpartum weight loss—but not for everyone, and not in a linear fashion. Some people lose weight during lactation; others hold onto weight until weaning. Both are normal. Hormonal shifts, metabolism, genetics, and stress levels all play a role.⁽³⁾

The Academy of Nutrition and Dietetics recommends approximately 0.5 kg of weight loss per week for 4 months during lactation, with a minimum intake of 1800 calories per day to return to prepregnancy weight without adversely affecting milk production. ⁽⁹⁾ According to researchers:

Commonly followed diets during the prepregnancy and lactation phases often lack nutritional adequacy, potentially leading to nutrient deficiencies that can adversely affect pregnancy outcomes. Women on restrictive diets may not meet their increased nutritional needs during lactation, highlighting the importance of a healthy, nutrient-dense dietary pattern and appropriate supplementation before conception to ensure optimal nutritional status ⁽⁴⁾ .

So yes, breastfeeding might help with weight regulation—but it's not a guaranteed weight loss plan, and restrictive eating and extreme exercise can backfire.

Here’s the good news: moderate and even intense exercise is safe while breastfeeding. In fact, it’s great for your mental health, cardiovascular health, and long-term physical well-being ⁽⁵⁾ .

A common myth is that exercise changes the “taste” of milk due to lactic acid buildup, deterring babies from nursing. Studies have shown this isn’t typically an issue—especially if you wait about 30 minutes after an intense workout to nurse ⁽⁶⁾ .

So go ahead: take that barre class, join that stroller workout group, or lace up for a walk-run. Just remember:

• Fuel your body before and after movement.

• Stay hydrated throughout the day .
  

• Listen to your body —fatigue and hunger are signals worth respecting.

Returning to movement after giving birth can feel like both a homecoming and a total reinvention. Your body just did something incredible—and it's still doing something incredible by nourishing a baby. But if you're craving more energy, mental clarity, or a sense of physical strength again, know this: exercise and breastfeeding can absolutely go hand in hand when approached with care, flexibility, and support. The goal isn’t to “bounce back”—it’s to rebuild, reconnect, and reclaim movement in a way that supports your healing and feels good in your body. Here are some of our favorite supportive exercise routines for postpartum breastfeeding mamas.

Don’t underestimate the power of a good walk. Whether it’s a stroller walk around the neighborhood, a nature trail with a friend, or a solo 20-minute power loop while baby naps, walking is a gentle but effective way to boost cardiovascular health, ease postpartum anxiety, and improve circulation—all without putting stress on your healing body. It’s also incredibly flexible: no special equipment, gym membership, or childcare required. Start with 10–15 minutes and build up gradually as your energy returns.

Before jumping into anything high-impact, reconnecting with your core and pelvic floor is essential. Pregnancy and birth can weaken these muscles, and working with a pelvic floor physical therapist or following a guided postpartum recovery program can help you safely rebuild strength. Think deep breathing, gentle ab engagement, and functional movements like glute bridges and bird-dogs. Supporting these foundational muscles not only helps you feel stronger—it can also reduce back pain, improve posture while breastfeeding, and prevent long-term issues like diastasis recti or incontinence.

Once cleared by your provider, you can start incorporating low-impact strength work . Bodyweight movements like squats, lunges, wall sits, and push-ups from your knees help you rebuild functional strength and stability. Focus on slow, controlled movements , and pair them with nourishing snacks and hydration to support your milk supply. Aim for short sessions—just 15–30 minutes a few times a week is more than enough to feel stronger without feeling depleted.

Postpartum yoga or Pilates can be a gentle gateway back into movement—especially styles that center breath, alignment, and strength over sweat and speed. These practices can help counteract the hunched-forward posture that often comes with nursing, baby-wearing, and co-sleeping. Bonus: many postpartum yoga routines include baby, making it an opportunity for bonding and movement all in one.

When you’re emotionally and physically ready, group fitness classes tailored to postpartum recovery —like Mom & Baby barre, stroller bootcamps, or postpartum-specific CrossFit—can be a fun way to build strength and community. Being around other moms who understand the exhaustion, leaky boobs, and need to pause for snack breaks is both empowering and encouraging. Just remember: comparison has no place here. Your pace is your power.

While moderate exercise is a green light, pairing it with restrictive diets —especially very low-calorie or low-carb ones—can put your milk supply at risk.

When the body enters a caloric deficit too steep for its needs, it may begin conserving energy. For some breastfeeding people, this results in a drop in prolactin , the hormone crucial for milk production ⁽⁴⁾ .

In addition, inadequate carbohydrate intake can reduce levels of insulin and leptin, both of which play indirect but important roles in the lactation cycle ⁽⁴⁾ . Your body sees this as a signal that now might not be the best time to nourish another human—and adjusts milk output accordingly.

If you’re in a season of rebuilding your relationship with your body, you're not alone. Many new moms struggle with body image—especially in a culture that pushes unrealistic "bounce back" timelines.

Here’s what we want to shout from the rooftops: You can love your body and want to care for it without overdoing it. Exercise can be joyful. Food can be nourishing. And healing happens when we give our bodies what they need—not when we deprive them.

If you find yourself constantly fatigued, ravenous, or seeing a dip in supply after a new fitness or diet routine, it’s time to check in:

• Are you eating enough?

• Are you allowing rest days?

• Are you hydrating and fueling after workouts?

• Are your goals realistic for this chapter of life?

If you’re navigating fitness, food, and feeding a baby all at once—you're doing a LOT. Comment your favorite postpartum exercises below and follow @legendairymilk on Instagram and TikTok for support through your breastfeeding journey. 

1. https://www.cdc.gov/breastfeeding-special-circumstances/hcp/diet-micronutrients/maternal-diet.html

2. https://kellymom.com/nutrition/mothers-diet/mom-calories-fluids/

3. https://pubmed.ncbi.nlm.nih.gov/9478032/

4. https://www.sciencedirect.com/science/article/pii/S001502822200485X?utm_source=chatgpt.com

5. https://www.acog.org/womens-health/faqs/exercise-after-pregnancy

6. https://laleche.org.uk/exercise-and-breastfeeding/

7. https://pmc.ncbi.nlm.nih.gov/articles/PMC5104202/

8. https://pmc.ncbi.nlm.nih.gov/articles/PMC7759779/

9. https://www.sciencedirect.com/science/article/pii/S001502822200485X