4 reasons intermittent fasting is not safe for pregnant people

The trendy diet should come with a warning label for anyone who's expecting.

Mercey Livingston CNET Contributor
Mercey Livingston is a health and wellness writer and certified Integrative Nutrition Health Coach. She's written about fitness and wellness for Well+Good, Women's Health, Business Insider, and Prevention.com among others. When not writing, she enjoys reading and trying out workout classes all over New York City.
Mercey Livingston
3 min read

Intermittent fasting is popular but not safe for pregnant women.

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Intermittent fasting is one of the most popular diets in the wellness world. Like many other trends in the wellness space that take hold, it's not the best or safest option for many people. And that includes pregnant and breastfeeding women.

"Intermittent fasting is a dieting strategy of limiting your consumption of calories to a certain window of time each day," says Dr. Sanaz Ghazal, an OB/GYN at Rise Fertility. "However, fasting is generally not recommended for women who are pregnant."

There are several reasons why intermittent fasting can be dangerous for both the expecting mom and unborn baby. Keep reading to find out more from Dr. Ghazal. 

1. Can increase risk for vitamin/nutritional deficiencies

Since intermittent fasting involves limiting when you eat to a certain window of time (usually a small window) it's really difficult to get all of the nutrition you need in a day. This is especially true for pregnant women who have high nutritional needs to support their health as well as the health of the unborn baby. 

"Pregnancy is a time to focus on healthy eating and consuming adequate nutrition to support you and your growing baby, not on weight loss," says Ghazal. "Intermittent fasting can potentially increase the risk of nutritional or vitamin deficiencies that can affect fetal development and even increase your risk of pregnancy complications," she says.

According to Johns Hopkins Medicine, you should be adding about 300 calories a day to your diet for a healthy pregnancy. Intermittent fasting can prevent you from getting your total requirement of daily calories and make it more difficult to consume the extra 300 calories you need per day.

2. May increase risk for preterm or premature birth

A 2019 study showed that fasting during the second trimester of pregnancy is especially risky for pregnant women. In the study, women who fasted in the second trimester had a 35% higher risk of delivering prematurely. Although the study was not designed around intermittent fasting windows specifically (the women in the study fasted during Ramadan and did not eat during daylight hours), intermittent fasting could look similar to this, but some forms of IF could be slightly less extreme. Bottom line: The study made clear that fasting is linked to preterm birth. 

3. Can cause low blood sugar

Gestational diabetes is associated with high blood sugar and is a serious risk for many pregnant women. But low blood sugar is also a cause for concern in pregnant women, according to Ghazal. Intermittent fasting can cause blood sugar to drop due to going long periods without eating. 

"Restrictive diets or prolonged periods of fasting during pregnancy can cause low blood sugar, which can cause you to feel lightheaded or faint and is associated with decreased fetal movement," says Ghazal.


Experts say intermittent fasting could impact milk supply in new moms.

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4. Milk supply and quality can be compromised 

Often referred to as the "fourth" trimester, the period of time after giving birth is also a physically demanding time that requires good nutrition. If you choose to breastfeed, you'll also have special nutritional needs to help support your milk supply. 

"It's important to understand that your body's metabolism and nutritional needs may change postpartum and while breastfeeding," says Ghazal. "Fasting for too long, restricting calories too much or rapid weight loss can significantly impact your milk supply and may even affect the composition of your breast milk," she says. 

What type of nutrition plan is best for pregnancy?

You should always consult your doctor or your dietician if you have questions about the specific nutrition needs you may have during pregnancy. Otherwise, it's important to focus on a healthy, balanced diet that supports you during a time of growth and change. 

"Instead of fasting or other extreme or restrictive diets during pregnancy, focus on eating a well-balanced diet with plenty of whole foods, organic fruits and vegetables and lean proteins," says Ghazal. Remember that some weight gain during pregnancy is normal, and you will lose pregnancy weight gradually after the baby is born. 

Other things Ghazal says to keep in mind is limiting coffee or caffeine consumption to 200mg a day, eliminate alcohol and remember to take a prenatal vitamin.

The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.