Is Fasting Safe During Pregnancy? What You Need to Know

Is Fasting Safe During Pregnancy? What You Need to Know

     Fasting during pregnancy is a significant concern for many expectant mothers, particularly in cultures and religions where fasting is traditionally observed for extended periods. Although religious and medical guidelines often exempt pregnant women from fasting, studies indicate that up to 90% still choose to fast for at least part of the fasting period to maintain cultural and familial connections.1

But before deciding to fast, have you consulted your healthcare provider? Have you assessed your health condition to ensure that fasting is safe for both you and your baby? Have you taken the necessary precautions to protect yourself and your baby? While many pregnant women choose to fast for cultural and religious reasons, it is essential to determine whether your body can handle it. Fasting during pregnancy may pose risks, and if your doctor advises against it, it could be dangerous for both maternal and fetal health.

This article examines whether fasting for extended periods or multiple days is safe during pregnancy, the potential effects on both maternal and fetal health and what scientific research reveals about fasting during pregnancy.

 

What Is Fasting and What Are Its Different Types?

 

Fasting is the practice of abstaining from food and sometimes drinking for a period longer than the usual overnight fast, often for religious, cultural or health reasons.2

There are various types of fasting and related restrictive diets, including:

 1. Calorie Restriction (CR): Involves a daily reduction of calorie intake by 15–40% without causing malnutrition.

 

2.Intermittent Fasting (IF): Involves alternating between periods of eating and fasting. Common forms of IF include:

a. Alternate Day Fasting (ADF): Fasting (0 kcal) every other day, alternating with normal food intake.

b. Time-Restricted Eating (TRE/TRF): Food intake is limited to a daily time window, typically 8–12 hours (e.g., 16:8 fasting, where food is eaten within 8 hours and fasting occurs for 16 hours).

c. 5:2 Diet (Periodic Fasting): Two days per week (either consecutive or non-consecutive), calorie intake is restricted to approximately 600 kcal per day, while normal intake is maintained on other days.

3. Long-Term or Prolonged Fasting (LF): Involves fasting for 2 to 21 days or more, where only minimal calories (200–250 kcal/day) are consumed.

4. Diets Derived from Fasting Strategies:

  • a. Very Low-Calorie Diet (VLCD): A controlled hypocaloric diet providing 800–1000 kcal/day with high protein content.

b. Fasting-Mimicking Diet (FMD): A low-protein, ketogenic diet that mimics fasting effects while still allowing some food intake (800–1100 kcal/day for 5 days).

 

5. Nutrient-Restricted Normocaloric Diets:

a. Ketogenic Diet (Carbohydrate Restriction): A diet very low in carbohydrates that forces the body into ketosis.

b. Protein or Amino Acid-Restricted Diets: Some diets limit proteins intake (such as methionine restriction) to promote longevity and metabolic health.3

 

Is It Safe for Pregnant Women to Fast?

 Scientific research on pregnant women is relatively limited due to ethical, legal and medical concerns, which also impacts the availability of data on fasting during pregnancy. However, with the limited data available, along with recommendations and guidelines, let’s explore this topic further. The safety of fasting during pregnancy depends on multiple factors including duration of fasting, the trimester of fasting, the mother’s overall health, nutritional intake before and after fasting and hydration levels.

Available scientific studies provide mixed results. However, prolonged fasting during pregnancy may negatively impact both maternal and fetal health, potentially leading to hypoglycemia, dehydration, ketosis, nutritional deficiencies, intrauterine growth restriction (IUGR), preterm birth, and neurodevelopmental complications.

 

  • Hypoglycemia: 

Hypoglycemia is typically characterized by a plasma glucose level of less than 70 mg/dL, but symptoms may not manifest until glucose levels fall below 55 mg/dL.4 But in pregnancy, Hypoglycemia is any blood sugar less than 70 mg/dl with or without symptoms. Eating too little or eating too late like skipping or delaying meals or snacks can cause hypoglycemia in some individuals. When it occurs you may feel shakiness, weakness, feeling lightheaded, hunger, irritability, a rapid heart rate, headache and feeling clammy (cold sweat).5 In non-diabetic pregnancies, severe hypoglycemic episodes are rare, but if maternal glucose levels drop significantly, it can affect both the mother and the developing fetus. Relative hypoglycemia is commonly observed in pregnant women with intrauterine fetal growth restriction (IUGR), even if they do not have diabetes.6

  • Dehydration: 
The relationship between hydration status (water intake) and fetal growth parameters such as birth weight, length, head circumference and chest circumference highlight the importance of hydration during pregnancy.7 Dehydration may limit blood volume and nutrient transport, which can impact fetal growth outcomes.

Hydration during pregnancy is crucial for maintaining the balance of amniotic fluid, which plays a vital role in fetal well-being. When the amniotic fluid level is insufficient, a condition known as oligohydramnios can occur.7 Oligohydramnios can be associated with several complications and risks that can affect both the mother and fetus, including restricted fetal growth, compromised lung development, cord compression, increased risk of preterm birth, labor complications.8

  • Ketosis: 
Ketone bodies are byproducts of fat metabolism that serve as an alternative energy source when glucose levels are low. During pregnancy, physiological changes in metabolism make pregnant women more prone to developing ketosis, even under normal conditions. An improper diet during pregnancy can lead to a mild to moderate increase in ketone body levels, as the body shifts to fat metabolism due to insufficient glucose availability. Additionally, increased glucose utilization and excretion lead to a more rapid drop in fasting blood glucose levels, making pregnant women more prone to starvation ketosis during prolonged fasting.9
  • Nutritional Deficiencies: 
Severe food deprivation, including malnutrition and famine, can lead to deficiencies in essential nutrients such as iron, calcium, protein, folic acid and others. This deprivation has been linked to preterm birth, growth restriction, and low birth weight. Some of these effects may be linked to a stress response that triggers early labor and pre-term delivery. Additionally, research suggests that prolonged fasting, such as multiple days of fasting during Ramadan, may increase the risk of hyperemesis gravidarum (severe form of nausea and vomiting during pregnancy that goes beyond typical morning sickness), lower birth weight and higher future child mortality. Therefore, adequate nutrition during pregnancy is essential for fetal growth and development, ensuring the best possible health outcomes for both the mother and baby.10
  • Intrauterine Growth Restriction (IUGR):
Intrauterine growth restriction (IUGR) is defined as a rate of fetal growth that falls below the normal range, considering the growth potential based on the race and gender of the fetus. It is often described as a deviation from or a reduction in the expected fetal growth pattern. Any mismatch between the nutrient supply provided by the placenta and the demand of the fetus can lead to intrauterine growth restriction (IUGR) which means IUGR occurs when the fetus does not receive enough nutrients and oxygen to grow at a normal rate, which can be caused by various factors such as placental insufficiency, maternal malnutrition or conditions that restrict blood flow to the placenta.11 This condition may result in low birth weight, developmental delays, and increased risks for health complications after birth .
 
  • Preterm Birth: 
Preterm birth is defined as the birth of babies who are born alive before completing 37 weeks of pregnancy. Fasting for extended periods or multiple days may increase the risk of preterm birth.12 For instance, fasting during the second trimester has been associated with a 35% higher risk of very preterm birth compared to not fasting. The risk is even more pronounced for women who fast during the latter half of the second trimester, such as during Ramadan.10
 
  • Neurodevelopmental complications: 
Nutrition during pregnancy is essential for maintaining life, but it is especially critical at the onset of life, during the antenatal and early life stages, when the growth and development of organs and systems are taking place. Malnutrition during pregnancy and early life, particularly resulting from an inadequate quantity or poor quality of nutrients consumed by the mother can have lasting effects on the offspring’s growth, metabolism, immune system as well as brain and cognitive development.13

 

 

Conclusion

 

     The impact of fasting on gestational length remains understudied, and therefore, there is no universal recommendation regarding the maximum fasting duration, as it largely depends on the individual’s health status. Short fasting periods, such as 8-12 hours, are generally well-tolerated in healthy pregnant women, provided they maintain proper hydration and nutrition before and after fasting. However, fasting periods exceeding 12 hours are typically not recommended and should be undertaken only under the supervision of healthcare professionals to minimize the risk of complications.

Although medical guidelines generally advise against fasting during pregnancy, if fasting is necessary due to religious or personal reasons, it is important to consult with a healthcare provider to assess whether fasting is safe during your pregnancy. Pregnant women should ensure they consume nutritious food and stay adequately hydrated before and after the fasting period to prevent complications like hypoglycemia, dehydration, ketosis, nutritional deficiencies, intrauterine growth restriction (IUGR), preterm birth and neurodevelopmental issues. Additionally, monitoring for any signs of weakness, dizziness or fetal distress is crucial. If any of these symptoms arise, immediate action should be taken to safeguard both maternal and fetal health.  

In conclusion, while fasting during pregnancy may be acceptable for short durations under specific conditions, it is vital to prioritize maternal and fetal well-being. Adequate hydration, proper nutrition and medical supervision are essential to ensure a healthy pregnancy. Always consult with a healthcare provider to determine the safest course of action based on individual health needs and circumstances.  

 

References
  1.  Glazier, J.D., Hayes, D.J.L., Hussain, S. et al.The effect of Ramadan fasting during pregnancy on perinatal outcomes: a systematic review and meta-analysis. BMC Pregnancy Childbirth. 2018;18:42. https://bmcpregnancychildbirth.biomedcentral.com/articles/10.1186/s12884-018-2048-y#citeas
  2. Visioli F, Mucignat-Caretta C, Anile F, Panaite SA. Traditional and Medical Applications of Fasting. Nutrients. 2022 Jan 19;14(3):433. https://pmc.ncbi.nlm.nih.gov/articles/PMC8838777/
  3. Wilhelmi de Toledo, Françoise & Grundler, Franziska & Sirtori, Cesare & Ruscica, Massimiliano. Unravelling the health effects of fasting: a long road from obesity treatment to healthy life span increase and improved cognition. Annals of Medicine. 2020;52:1-15. https://www.researchgate.net/publication/342091120_Unravelling_the_health_effects_of_fasting_a_long_road_from_obesity_treatment_to_healthy_life_span_increase_and_improved_cognition
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  5. Kaiser Permanente. Hypoglucemia (low blood sugar) during pregnancy. Kaiser Foundation Health Plan of the northwest. Accessed on March 03,2025. Available from: https://healthengagement.kaiserpermanente.org/wp-content/uploads/14665-hypoglycemia-during-pregnancy-ada-english.pdf
  6. Bengt Persson, Ulf Hansson. Hypoglycaemia in pregnancy. Baillière’s Clinical Endocrinology and Metabolism. 1993;7(3):731-739. https://www.sciencedirect.com/science/article/abs/pii/S0950351X05802162
  7. Mulyani EY, Hardinsyah, Briawan D, Santoso BI, Jus’at I. Effect of dehydration during pregnancy on birth weight and length in West Jakarta. J Nutr Sci. 2021 Aug 27;10:e70. https://pmc.ncbi.nlm.nih.gov/articles/PMC8411261/
  8. Keilman C, Shanks AL. Oligohydramnios. [Updated 2022 Sep 12]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan. Accessed on march 03,2025 Available from: https://www.ncbi.nlm.nih.gov/books/NBK562326/
  9. Qian M, Wu N, Li L, Yu W, Ouyang H, Liu X, He Y, Al-Mureish A. Effect of Elevated Ketone Body on Maternal and Infant Outcome of Pregnant Women with Abnormal Glucose Metabolism During Pregnancy. Diabetes Metab Syndr Obes. 2020 Nov 25;13:4581-4588. https://pmc.ncbi.nlm.nih.gov/articles/PMC7701151/#abstract1
  10. Rasmi M Tith, Marianne Bilodeau-Bertrand, Ga Eun Lee, Jessica Healy-Profitós, Nathalie Auger. Fasting during Ramadan Increases Risk of Very Preterm Birth among Arabic-Speaking Women. The Journal of Nutrition. 2019;149(10):1826-1832. https://www.sciencedirect.com/science/article/pii/S0022316622164564#:~:text=During%20pregnancy%2C%20adequate%20nutrition%20is,weight%20(3%2C%204).
  11. Sharma D, Shastri S, Sharma P. Intrauterine Growth Restriction: Antenatal and Postnatal Aspects. Clin Med Insights Pediatr. 2016 Jul 14;10:67-83. https://pmc.ncbi.nlm.nih.gov/articles/PMC4946587/#sec5
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