Can Exercise and Dieting Affect Your Milk Supply?

An Evidence-Based, Compassionate Guide for Breastfeeding Parents

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

If you’re breastfeeding in the postpartum phase, you’re already carrying a lot. Feeding schedules, broken sleep, hormonal changes, and often a very different relationship with your body. It’s common to start wondering:

• Can I safely exercise while breastfeeding?
• Will dieting affect my milk supply?
• Why does my supply sometimes dip after workouts?

The good news is that exercise and breastfeeding can absolutely coexist. How you fuel, hydrate, and recover matters more than the exercise itself.

Let’s break this down with science, empathy, and zero shame.

How Lactation Affects Your Metabolism

Breast milk production is biologically incredible and energetically demanding.

Producing milk requires an additional 450–500 calories per day. This is roughly equivalent to a 8 km run or an intense hour-long cycling session. This energy demand is nearly 20% higher than pregnancy.

To maintain a steady milk supply, your body needs:

• Adequate calories
• Carbohydrates, protein, and healthy fats
• Sufficient hydration and electrolytes

When these needs aren’t met, especially alongside exercise, your body may conserve energy by temporarily reducing milk output.

Why Milk Supply Can Drop After Exercise

If you’ve noticed lower output after returning to movement, you’re not imagining it. Several physiological factors can contribute.

1. Calorie Deficit and Energy Conservation

Milk production is hormonally driven and energy-dependent. When your body senses a calorie shortfall, often from increased exercise without increased intake, it prioritises basic survival and recovery.

Since lactation isn’t essential to maternal survival, milk production may temporarily down-regulate.

This is more likely if you:

• Eat less than your lactation needs
• Skip meals or post-workout snacks
• Exercise fasted or consistently under-fuel

Think of it like this. Less fuel in leads to less output out.

2. Glycogen Depletion and Stress Hormones

High-intensity or long workouts deplete glycogen, your body’s stored carbohydrates. When glycogen runs low, cortisol rises to free up energy.

Elevated cortisol can interfere with:

• Prolactin, the milk production hormone
• Oxytocin, the let-down reflex hormone

Without replenishing carbs post-workout, let-downs may feel delayed and pumping sessions less productive.

3. Dehydration and Electrolyte Loss

Even mild dehydration can reduce plasma volume, which directly impacts milk volume.

Sweating during exercise without adequate fluid and electrolyte replacement can lead to temporary dips in supply, especially in hot or humid climates.

Tip. Aim for at least 16 to 20 oz of fluid post-workout and consider electrolytes to support hydration and recovery.

4. Inadequate Protein and Healthy Fats

Lactation increases protein needs to support:

• Breast tissue repair
• Hormone production
• Milk composition

Low protein or insufficient essential fats, especially DHA, can affect both maternal recovery and milk quality.

5. Nervous System Stress

Exercise is still a form of physical stress. While moderate movement supports mental health and circulation, excessive intensity without recovery can activate the stress response, making let-downs harder and nursing more frustrating.

Breastfeeding and Weight Loss What Research Actually Shows

The idea that breastfeeding automatically leads to weight loss is over-simplified.

Some parents lose weight while nursing. Others hold onto weight until weaning. Both are completely normal.

Weight changes during lactation are influenced by:

• Hormones
• Genetics
• Stress and sleep deprivation
• Nutrient intake

The Academy of Nutrition and Dietetics recommends no more than 0.5 kg of weight loss per week and a minimum of 1,800 calories per day during lactation to protect milk supply.

Restrictive dieting during breastfeeding is linked to nutrient deficiencies and may negatively impact both maternal health and milk production.

Is Exercise Safe While Breastfeeding?

Yes. Exercise is safe and beneficial while breastfeeding, including moderate to vigorous movement.

Benefits include:

• Improved cardiovascular health
• Better mood and mental health
• Improved insulin sensitivity and circulation

A common myth is that exercise makes milk taste sour due to lactic acid. Research shows this is rarely an issue, especially if you wait about 30 minutes after intense workouts before nursing.

The key isn’t avoiding exercise. It’s fuelling appropriately.

Postpartum Exercise That Supports Milk Supply

Walking

Low-impact, flexible, and effective. Walking improves circulation, reduces anxiety, and supports recovery with minimal stress on the body.

Pelvic Floor and Core Reconnection

Gentle breathing, core engagement, and guided postpartum rehab help rebuild foundational strength and support posture during nursing.

Low-Impact Strength Training

Short, controlled sessions of 15 to 30 minutes using bodyweight movements can rebuild functional strength without depleting energy reserves.

Yoga or Pilates

Postpartum-specific classes support posture, breath, and nervous system regulation, all helpful for milk let-down.

Group Fitness When Ready

Postpartum-friendly classes offer community and motivation. Just remember that comparison doesn’t belong here.

Where Things Can Go Wrong: Restriction and Intensity

Problems arise when intense training is paired with restrictive diets, especially very low-calorie or low-carb plans.

Severe deficits can:

• Lower prolactin levels
• Reduce insulin and leptin signalling
• Signal the body to conserve energy

In response, milk supply may decrease.

You Deserve to Feel Strong Not Depleted

Postpartum bodies don’t need punishment. They need support, nourishment, and patience.

If you notice fatigue, hunger, mood changes, or supply dips after changing your routine, pause and check in:

• Are you eating enough
• Are you resting between workouts
• Are you hydrating and refuelling properly
• Are your expectations realistic for this season

Rebuild With Fuel Not Restriction

Exercise and breastfeeding can coexist beautifully when your body is properly supported.

Focus on:

• Nourishment over restriction
• Strength over speed
• Sustainability over perfection

You’re doing something extraordinary already.

For more evidence-based breastfeeding support, follow @legendairymilksg on Instagram and TikTok and remember your body isn’t behind. It’s healing.