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Intermittent Fasting During Pregnancy: Safety And Risks

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How safe is intermittent fasting while pregnant? Although studies state that intermittent fasting has many health benefits, learn about its safety in pregnancy. Intermittent fasting is a diet routine that cycles between brief periods of fasting and eating within a fixed time frame. You can plan your intermittent fasting in different ways, such as 16:8 (fasting 16 hours a day and eating in an eight-hour window), an alternate-day fast, 5:2 (eating normally for five days and fasting two days a week) (1).

Though it is generally considered safe, read on to know the potential health risks and safety concerns associated with intermittent fasting while you are pregnant.

How Does Intermittent Fasting Work?

When individuals eat three main meals and two snacks a day and do no exercise, they utilize the calories (glucose) from the food, leaving their fat stores untouched. However, when they fast for hours, their body utilizes all the stored glucose stores and triggers fat burnout (ketosis).

When the body metabolizes fat, it produces ketones, which are used as the main energy source instead of glucose. This metabolic switch combined with fasting helps (1) (2) (3):

  • Lower blood cholesterol and improves lipid profile
  • Improve glucose or blood sugar regulation, reducing the risk of diabetes
  • Reduce abdominal or belly fat and lower blood pressure
  • Alleviate oxidation and inflammation
  • Improve memory

While intermittent fasting looks so beneficial, it isn’t the right choice for everyone.  

Can You Do Intermittent Fasting When Pregnant?

No. Fasting or restrictive eating during pregnancy isn’t advisable. Instead, experts advise pregnant women to make any dietary or lifestyle changes during pregnancy in consultation with their healthcare provider.

Generally, the research studies on the effects of intermittent fasting throughout pregnancy are sparse, and the studies that exist have small sample sizes or shorter study duration. Also, the results of these studies are mixed.

  • A 2006 study conducted on 168 pregnant women concluded that “maternal diet restriction is associated with an increased risk of gestational diabetes (GDM) and induction of labor. The frequency of neonatal admission to special care baby units (SCBU) has increased (4).” 
  • In contrast, a 2021 case report and review study showed that dietary measures, including intermittent fasting, caloric restriction, and exercise, can increase insulin sensitivity, reduce body fat, correct fetal growth abnormalities, and enhance a mother’s mood (5).

However, more studies are required to confirm these findings. Additionally, research studies need to evaluate the possibility of any adverse effects, such as pregnancy loss. Due to these shortfalls, no recommendations can be made on the safety and efficacy of intermittent fasting for pregnant women.  

What Are The Health Risks Of Intermittent Fasting During Pregnancy?

Pregnancy is a phase where eating well is essential to ensure your baby gets ample nourishment to gain weight and develop properly. In fact, eating well is crucial for you as well for gaining weight and developing fat stores to facilitate delivery and support breastfeeding. In such a scenario, eating less than recommended or fasting during pregnancy to manage or lose weight can lead to nutritional deficiencies, such as iron deficiency anemia, affecting your and your baby’s health. Also, it may cause the baby to have a low birth weight.

According to the American Society of Nutrition (ASN), “energy restriction during pregnancy is known to increase risk of preterm birth (6). This risk is higher when women fast during the second and third trimester of pregnancy when the energy needs of a mother are higher than during the first trimester. Another study showed that fasting during pregnancy could affect fetal breathing movement, indicating the negative effects of fasting during pregnancy (7).

What If You Were Practicing Intermittent Fasting Before Pregnancy?

Maintaining your weight (or BMI) within healthy ranges before pregnancy is crucial to ensure healthy weight gain during pregnancy. It is why several women opt for different weight loss approaches, such as intermittent fasting, to lose weight before pregnancy. If you were on intermittent fasting before conception, whether or not to continue with it during pregnancy is a decision you should make in consultation with your doctor. Remember, the right weight gain during pregnancy is vital for a healthy pregnancy.  

How To Control Your Weight Gain During Pregnancy?

Healthy weight gain during pregnancy doesn’t require restricted eating or fasting. Instead, you need to eat a balanced diet and keep a close watch on your daily calorie intake. Most healthy pregnant women require an additional 340 calories a day during the second trimester and 450 calories during the third trimester (8).

You can get these extra calories by incorporating moderate amounts of various nutrient-rich, healthy foods into your diet. In addition, staying active and indulging in pregnancy-safe exercises is another healthy lifestyle practice that can help you keep your weight within desired limits. Experts suggest that eating healthy and exercising regularly during pregnancy can help gain healthy weight and avert health problems for you and the baby (9).

Can Intermittent Fasting Help When Trying To Conceive?

Several studies show that intermittent fasting may have beneficial effects on fertility (10). For instance, a 2021 study found that “low-carbohydrate dietary patterns along with intermittent fasting may help individuals with insulin resistance not only lose weight but also increase their insulin sensitivity (11).” Insulin insensitivity or resistance is known to affect fertility in women.

Another study highlighted that obese women with polycystic ovarian syndrome (PCOS), when fasted regularly, saw an increase in luteinizing hormone (LH) levels. LH is a vital hormone responsible for facilitating ovulation (12). These promising results show that intermittent fasting, when done under a doctor’s guidance, may help improve a woman’s fertility.

Intermittent fasting is a cyclic eating pattern that can promote health and well-being in general. However, since its effect on pregnancy outcomes for the mother and the baby are still under research, no recommendations can be made regarding its safety during pregnancy. Remember, fasting during pregnancy is generally not advisable as it can cause nutrient deficiencies, leading to adverse outcomes, such as preterm delivery.

References:

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  1. Research on intermittent fasting shows health benefits.
    https://www.nia.nih.gov/news/research-intermittent-fasting-shows-health-benefits
  2. Intermittent Fasting: What is it, and how does it work?
    https://www.hopkinsmedicine.org/health/wellness-and-prevention/intermittent-fasting-what-is-it-and-how-does-it-work
  3. The benefits of intermittent fasting.
    https://www.ucihealth.org/blog/2020/01/intermittent-fasting
  4. Hisham M Mirghani and Omer AHamud; (2006); The effect of maternal diet restriction on pregnancy outcome.
    https://pubmed.ncbi.nlm.nih.gov/16450268/
  5. Amira Mohammed Ali and Hiroshi Kunugi; (2020); Intermittent Fasting, Dietary Modifications, and Exercise for the Control of Gestational Diabetes and Maternal Mood Dysregulation: A Review and a Case Report.
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7765295/
  6. Fasting during the second trimester of pregnancy may be particularly harmful.
    https://nutrition.org/fasting-during-the-second-trimester-of-pregnancy-may-be-particularly-harmful/
  7. HM Mirghani et al.; (2009); The effect of intermittent maternal fasting on human fetal breathing movements.
    https://www.tandfonline.com/doi/abs/10.1080/01443610400007844
  8. Healthy Weight during Pregnancy.
    https://www.eatright.org/health/pregnancy/prenatal-wellness/healthy-weight-during-pregnancy
  9. Health Tips for Pregnant Women.
    https://www.niddk.nih.gov/health-information/weight-management/healthy-eating-physical-activity-for-life/health-tips-for-pregnant-women
  10. LunHua et al.; (2020); Time‐restricted feeding improves the reproductive function of female mice via liver fibroblast growth factor 21.
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7533054/
  11. Megan W Arbour et al.; (2020); Clinical Implications for Women of a Low-Carbohydrate or Ketogenic Diet With Intermittent Fasting.
    https://pubmed.ncbi.nlm.nih.gov/33838849/
  12. Pradeep M. K. Nair and Pranav G. Khawale; (2016); Role of therapeutic fasting in women’s health: An overview.
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4960941/
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Swati Patwal

Swati Patwal is a clinical nutritionist and toddler mom with over eight years of experience in diverse fields of nutrition. She started her career as a CSR project coordinator for a healthy eating and active lifestyle project catering to school children. Then she worked as a nutrition faculty and clinical nutrition coach in different organizations. Her interest in scientific writing... more