Why Can't You Fast When Breastfeeding?

October 25, 2025 •

4 min read

Lactation requires an additional 330-500 calories per day, putting a significant demand on a mother's body. This increased energy and fluid requirement is the main reason why you can't fast when breastfeeding, as it can deplete the mother's resources and compromise milk production, impacting both maternal and infant health.

Quick Summary

Fasting while nursing poses risks to both mother and baby due to intense caloric and hydration demands. It can cause dehydration and compromise milk supply, especially for mothers of exclusively breastfed infants under six months. Health professionals generally advise against prolonged fasting, recommending prioritizing consistent nutrition for optimal health and lactation.

Key Points

High Caloric Demand: Breastfeeding requires an additional 330-500 calories per day, which is compromised by fasting.
Dehydration Risk: Fasting restricts fluid intake, which can cause maternal dehydration and decrease milk volume, as breast milk is primarily water.
Low Milk Supply: Prolonged or severe caloric restriction can significantly reduce milk supply, especially in the early postpartum period.
Nutrient Depletion: While macronutrients may be buffered, fasting can decrease the level of vital micronutrients like zinc, magnesium, and potassium in breast milk.
Maternal Fatigue: Inadequate calories during fasting can cause excessive fatigue, dizziness, and difficulty managing the demands of caring for an infant.
Infant Growth Concerns: A reduced or less nutritious milk supply can impact infant weight gain and overall growth, particularly for exclusively breastfed babies.
Expert Guidance is Crucial: Any consideration of fasting while breastfeeding should involve consultation with a healthcare provider to create a safe, personalized plan.

The Physiological Demands of Lactation

Breastfeeding is an energy-intensive process, requiring a mother to consume approximately 330 to 500 extra calories and significant additional fluids daily. This high demand is critical for producing the recommended 750mL or more of breast milk per day during the first six months of exclusive breastfeeding. When a mother fasts, her body enters a state of caloric deficit, which can interfere with the complex balance required for healthy milk production. The body's priority shifts to preserving the mother's energy stores, potentially at the expense of milk volume or nutrient quality.

The Impact of Fasting on Milk Supply and Composition

One of the most immediate concerns with fasting while breastfeeding is its effect on milk supply. While short-term fasting (less than 12-14 hours) may not drastically impact the overall quantity for a well-nourished mother with an established milk supply, prolonged fasting significantly increases the risk of a noticeable drop in milk production. Studies conducted during Ramadan have shown that while macronutrients like fat and protein might not change significantly in the short term, levels of critical micronutrients such as zinc, magnesium, and potassium can be negatively affected. Furthermore, inadequate fluid intake from fasting can directly reduce milk volume, as breast milk is comprised of about 87% water.

Maternal and Infant Health Risks Associated with Fasting

Fasting during lactation presents several health risks for the mother. Dehydration is a primary concern, potentially leading to fatigue, headaches, dizziness, and reduced milk volume. A significant caloric deficit can also cause extreme fatigue, making it challenging for a mother to care for herself and her baby. In rare but serious cases, prolonged fasting can lead to ketoacidosis, a dangerous metabolic state. For the infant, the consequences are tied to the mother's health. A reduced milk supply can lead to poor weight gain and dehydration, especially for babies exclusively reliant on breast milk. A baby's growth and development can also be compromised if consistent nutrition is not maintained.

Situations Where Fasting is Especially Risky

Not all breastfeeding journeys are the same, and some situations make fasting particularly hazardous. It is generally not recommended for mothers with babies under six months old, as their milk supply is still being established and the infant is exclusively dependent on breast milk. Mothers with a history of low milk supply, chronic illnesses like diabetes, or a history of eating disorders should also avoid fasting. The demands of nursing multiples (twins, triplets) also make consistent, high caloric and fluid intake non-negotiable.

Fasting Protocols vs. Breastfeeding Needs: A Comparison


Aspect	Extended Fasting (e.g., 24+ hours)	Breastfeeding Needs	Conflict/Compatibility
Energy (Calories)	Severe caloric deficit intended for weight loss	Requires 330-500 extra kcal/day to produce milk	High Conflict: Fasting directly contradicts the high energy demands of lactation, leading to fatigue and supply issues.
Hydration (Fluids)	No food or drink for prolonged periods (e.g., dawn to dusk)	Requires 2.7-3+ liters of fluids daily to support milk production	High Conflict: Eliminating fluid intake causes dehydration, which immediately impacts milk volume.
Nutrient Intake	Limited intake of macronutrients and micronutrients	Needs consistent supply of protein, fat, vitamins (zinc, magnesium, potassium)	Moderate Conflict: Macronutrients are buffered in the short term, but micronutrient levels can drop significantly with prolonged fasting.
Maternal Hormones	Affects hormones like insulin and cortisol, indicating stress	Requires balanced hormonal environment for milk letdown (prolactin, oxytocin)	Moderate Conflict: Fasting-induced stress can inhibit oxytocin, interfering with the milk ejection reflex.
Body's Priority	Energy conservation and fat burning for survival	Nourishment of the infant via milk production	High Conflict: The body prioritizes survival over milk production during starvation mode, potentially decreasing supply.

Safer Approaches and Expert Recommendations

For mothers who wish to incorporate some form of fasting, especially for religious reasons, healthcare professionals often suggest modified, gentle approaches and robust pre-planning. This involves limiting fasting windows, ensuring proper hydration during non-fasting periods, and eating nutrient-dense foods. An overnight fast of 12-14 hours may be tolerable for mothers with a well-established supply, especially after the first six months postpartum when solids are introduced. Continuous monitoring of both maternal health and infant well-being is essential. Signs like dizziness, persistent headaches, or a decrease in wet diapers for the baby are red flags to break the fast immediately. Consulting a doctor or a lactation consultant is crucial before attempting any fasting regimen while breastfeeding.

Conclusion: Prioritizing Infant Needs Above All

The fundamental reason you can't fast when breastfeeding is that your body's priority is sustaining your infant. Lactation places a high and consistent demand on your caloric intake, hydration, and nutrient reserves. Fasting can jeopardize these critical resources, potentially leading to a drop in milk supply, dehydration, and a decline in maternal well-being. While some modified or short-term fasting may be possible under expert supervision for mothers with a well-established supply, the risks associated with prolonged fasting outweigh the potential benefits. The safest and most recommended approach is to prioritize consistent nourishment to support a healthy breastfeeding relationship and ensure the optimal development of your baby. For comprehensive guidance, consider reviewing the guidelines from the Centers for Disease Control and Prevention (CDC).

Frequently Asked Questions

For mothers with a well-established and stable milk supply, a short fast (e.g., one day) is unlikely to cause a permanent or significant drop. However, it can lead to temporary dehydration and fatigue, and increased nursing may be needed the following day to restore supply.

Strict intermittent fasting is not recommended, especially in the first six months. Gentle, time-restricted eating (like a 12-14 hour overnight fast) might be possible for some mothers with established milk supplies, but requires close monitoring and a nutrient-dense eating window.

Signs include your baby appearing less satisfied or fussier after feeds, fewer wet or dirty diapers, and slower weight gain. For the mother, breasts may feel less full, and you might experience increased fatigue or dizziness.

Many religions exempt breastfeeding women from fasting. If a mother decides to fast, it should only be after consulting a doctor and with extreme caution, particularly if the baby is over six months and consuming solids. It is important to stay hydrated during non-fasting hours and break the fast if feeling unwell.

Immediately break your fast by drinking fluids and eating a nutritious meal. Focus on rehydrating and eating regularly over the next 24-48 hours. If you notice a drop in milk supply, increase nursing or pumping sessions. Consult a doctor if you feel unwell.

Signs of dehydration in a baby include fewer wet diapers (less than 6-8 in 24 hours), dark or strong-smelling urine, a sunken soft spot (fontanelle) on their head, dry mouth, or cold hands and feet.

During your eating window, focus on nutrient-dense foods. This includes proteins like lean meat, fish, and legumes; complex carbohydrates like whole grains; healthy fats like avocado and nuts; and hydrating fruits and vegetables. Ensure you consume enough calories to support milk production.