Intermittent fasting has recently gained more attention – and for good reason! The benefits of intermittent fasting have been backed by science. They include weight loss, improved blood sugar, improved chronic health conditions, metabolic flexibility and support, and longevity.

As a dietitian, I see first-hand on a daily basis how intermittent fasting can be an amazing tool for weight loss and improved overall health. However, intermittent fasting needs to be done correctly in order to reap the benefits.

More specifically, women need to fast differently than men, taking our menstrual cycle into account to ensure we are supporting our hormones and metabolism. The hormonal variations women experience throughout their menstrual cycle control important aspects of nutrition, including metabolism, hunger and cravings. For this reason, not taking hormonal fluctuations into account can lead to some difficulties when it comes to reaching health goals.

If we neglect to fast according to our cycle, we may run into adverse effects such as weight gain, inability to lose weight, irregular menstrual cycles and insatiable cravings/hunger.

Over the last 4 years, I have helped clients figure out the best intermittent fasting schedule for them. The approach I’ll outline in this article combines research from Dr. Mindy Pelz, a noted expert in this field, with my experiences working with clients.  

Let’s dive deep into the science behind cycle syncing intermittent fasting to discuss the optimal way to fast according to our menstrual cycle. 

Intermittent Fasting with a Menstrual Cycle: Fasting During the Fertility Years

Women who menstruate experience a lot of hormonal changes throughout the month that can impact the benefits of fasting. Here are some general guidelines on cycle syncing intermittent fasting:

Days 1-10: From day 1 (the first day of your period) through day 10 of a woman’s cycle, there are fewer restrictions when it comes to fasting. Women are able to fast for 15+ hours and even 24-36 hours if desired. In this phase, estrogen and progesterone levels are lower, and overall appetite is lower. This makes it a favorable time to fast.

Days 12-20: During the follicular phase, days 12 through 20, it is recommended that women do not exceed a 15-hour fast. Focus on eating higher-protein foods, like grass-fed meats, organic poultry and wild-caught seafood, and an overall lower carbohydrate intake.

Days 21-28: NO fasting. During this time, the body needs increased carbohydrates and potentially more calories overall. It is recommended that women do not fast during this time to support their energy and metabolic needs. Fasting during this time can have negative effects on hormones, causing weight gain and increased inflammation.

Intermittent Fasting and Perimenopause

Perimenopause is a transitional time between your fertility years and menopause. It can happen at different times for different women.Ssome women experience symptoms starting in their 30s and others experience them in their late 40s. Some characteristics of perimenopause include irregular menstrual cycles, abdominal weight gain and/or inability to lose weight, increased fatigue, and hot flashes.

During this time, women should try to track their cycles. This can be difficult, as cycles become very inconsistent. But picking up on hormonal patterns is key to knowing when to fast.

If you have consistent cycles, fast as you would in your fertility years.

If you have inconsistent cycles and are unable to track patterns, it can be worth a DUTCH test (dried urine test for comprehensive hormones) to determine your progesterone and estrogen levels. These can be done with your doctor or with an at-home test. You can also watch for symptoms (listed below) to determine if you have elevated estrogen or progesterone levels.

If you have elevated estrogen levels: Fast

Symptoms of elevated estrogen include midsection weight gain, chronic fatigue, low libido, and irregular menstrual cycles

If you have elevated progesterone levels: Don’t fast 

Signs of progesterone include spotting, increased hunger and fatigue, anxiety, and cramping. Instead of fasting, increase your intake of whole-food carbs like rice, fruit, chickpeas, beans and other legumes.

Intermittent Fasting and Menopause

During menopause, we have much more freedom when it comes to intermittent fasting. Want to do intermittent fasting most days, and that feels good to you? Do it! Want to try longer fasts for autophagy over 17 hours? Do it! At this time, you can even try a longer fast – anywhere from 24 hours to 3 days. 

Dr Mindy Pelz does recommend not fasting 1 day a week to support progesterone levels. The benefits can include improved insulin sensitivity, increased ketone production, autophagy (the processing and removal of old cells), immune system restoration, and neurotransmitter support, which could reduce anxiety and depression.

During this time, it’s still very important to listen to your body. If you notice stubborn weight gain, irritability, anxiety or bloating, play around with your fasting schedule – maybe don’t do it as often or switch up the hours.

As a Registered Dietitian who believes in the power of fasting, I often create customized meal plans for my clients and have them pair intermittent fasting with the plans. Time-restricted eating combined with an individualized plan has shown to provide the greatest results for my clients.

Case Study: How Intermittent Fasting Helped One of My Clients Get off Her Diabetes Medication

Cycle syncing intermittent fasting can help women lose weight and improve their overall health. Many of my clients have experienced the benefits of intermittent fasting, but some of the transformations are more dramatic than others. Here’s an example.

When I first met Cheryl*, she had uncontrolled diabetes. Her A1c levels were 12.3 (anything above 9 is considered dangerous). She was also experiencing weight gain.

My nutrition recommendation was a high-protein, low-glycemic customized plan combined with intermittent fasting. We started having regular check-ins with dramatic results:

• 2-month progress: Cheryl lost 13 pounds, and her A1c dropped from 12.3 to 6.4. She reduced her diabetes medication from twice daily to once daily and experienced increased energy
• 3-month progress: Cheryl lost 26 pounds, and her fasting blood sugar reduced from over 200 to 84-96 in the morning
• 4-month progress: Cheryl’s doctor advised her to discontinue all diabetic medications. She was now following a gluten-free, high-protein diet, limiting added sugars, and continuing to combine her customized plan with intermittent fasting to continue on her way to reversing insulin resistance

Cheryl tried intermittent fasting from 12 hours to as long as 16 hours and reports it has helped her ‘jump start decreasing [her] blood sugar & weight!’ With a solid plan in place, she was able to regain control over her body and feel like herself again.

Bottom Line

Intermittent fasting can be a powerful tool for weight loss and overall health gains. Whether you are trying to lose weight, develop healthier eating habits or manage a chronic condition like diabetes, intermittent fasting can be beneficial when you follow your cycle.

Of course, be intuitive with your body. Pay attention to your energy levels, hunger cues and cravings. If you ever have questions, check in with your healthcare provider to make sure your intermittent fasting plan is working for your body.

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*Name has been changed to protect my client’s privacy.