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To Fast or Not to Fast, that is the Question!

To Fast or Not to Fast, that is the Question!
Fasting is an increasingly hot topic in the fertility space and both women and men question if they should be fasting to boost their chances of getting pregnant. While research has shed light on many health benefits of fasting for the general population, not many studies have been done on fasting’s impact on fertility. So, how do you decide whether to implement fasting or determine if it’s safe? Let’s take a look!

What is Fasting?

Fasting is the abstinence from eating and sometimes drinking for health, ritual, religious, or ethical reasons. There are several forms of fasting, but two of the most popular used today include:


  • Intermittent fasting (IF) which is a pattern of eating where you alternate between calorie-restricted and non-calorie-restricted eating. One example of IF is the 5:2 protocol where you limit your intake to ~400-600 calories (approximately 25% of your total calorie intake) on 2 non-consecutive days of the week. Another example is Complete Alternate Day Fasting where no food is eaten over a 24-hour period one or more non-consecutive days of the week. People often use the phrase “intermittent fasting” for various forms of fasting, but they are not all the same. 


  • Time-restricted eating (TRE) involves narrowing the window of time you eat but does not restrict calories. For example, 12:12 TRE is when you fast for 12 hours overnight and eat within a 12-hour window, such as 7am – 7pm. Very common is the 16:8 TRE pattern where a person fasts for 16 hours followed by an 8-hour eating window. TRE is one of the most popular and widely practiced forms of fasting

What are the Benefits of Fasting?

For the general population, there are several known health-boosting benefits of fasting:


  • Improved blood sugar balance and insulin sensitivity
  • Reduced inflammation and oxidative stress
  • Positive changes to the gut microbiome/gut health
  • Lower blood pressure
  • Improved ability to burn fat for energy
  • Inhibition of certain types of cancer and delayed tumor growth
  • Improved athletic performance 
  • Improved cognitive function
  • Increased energy levels

Should I Fast for Fertility? 

As mentioned above, limited studies have been done specifically on the impact of fasting on fertility, so caution should be taken. Fasting will impact each person differently and how it impacts you will depend on your unique circumstances. However, a recent study does suggest that IF may support fertility in women with high androgen levels. This is often seen in women with insulin resistance and polycystic ovarian syndrome (PCOS). Also, TRE may increase levels of sex hormone-binding globulin in women with obesity, especially those who stopped eating by 4pm. Yet, more is not always better! Limiting your calories or narrowing your window of eating too much can result in the brain sending signals to your body that may reduce or stop ovulation altogether.  


In the above study, it suggests that IF may actually reduce testosterone and androgen levels (which can reduce libido) in already lean, active, young males. When it comes to supporting fertility, it seems that IF and TRE may provide the greatest benefits to men who are overweight, obese, or have high levels of inflammation and/or oxidative stress. 


If you are planning to become pregnant and want to explore the idea of fasting, it is important that you work with a trained licensed practitioner who can do baseline lab testing and monitor your progress. However, once a woman becomes pregnant, IF and TRE are not recommended! You want to honor your hunger cues and eat whenever is necessary for you and your baby. This is not the time for restriction, rather a time to focus on listening to and nourishing your body!  

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Lisa Dreher

Lisa Dreher

Lisa is a registered dietitian/nutritionist with a Master’s Degree in Nutrition and Integrative Health. She has been practicing for over a decade and works full time at Dr. Mark Hyman's UltraWellness Center in Lenox, Massachusetts.

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