SIMPLE’s guide to intermittent fasting during your period

Written by Melissa Renae

Medically reviewed by Louise Bula, RD

You’re just minding your business, ticking things off your to-do list (is it us, or does that thing get longer every day?), and quietly making progress. 

Then BAM — along comes the monthly gift from your reproductive cycle to make life that much more … interesting. 

You’ve heard intermittent fasting is an easier way to help manage your health — and that sure sounds like a good thing with everything else you have going on — but you’ve got some questions.

Is it safe to continue intermittent fasting during your period? Can fasting affect your period? Would you need to make changes to your fasting schedule during menstruation? Could intermittent fasting have stopped my period?

All of this along with “What’s for dinner tonight?” Sheesh.

Don’t worry, we’ve got your back on everything to do with intermittent fasting and periods. (FYI, we can hook you up with dinner ideas, too.) 

Key takeaways

• Intermittent fasting on your period can be safe and beneficial if done with care.
• Increasing three key nutrients in your diet is important for successfully mixing fasting and your menstrual cycle.
• Getting to know your cycle and your needs is important for deciding if intermittent fasting while on your period is right for you.
• Certain food choices can support your body (and results) during different menstrual phases. 

Is intermittent fasting a good idea for women on their periods? 

Intermittent fasting can be safe and effective for women, but a slower, gentler approach could help to reduce any risks, especially when fasting during your period.

Fasting can be more complicated for women than it is for men. A big reason why is the difference in hormones and how women’s bodies respond to calorie restriction (check out intermittent fasting for women for a deeper dive). This is especially true when it comes to menstrual cycles. 

One exception may be for women with PCOS or hyperandrogenism. Although the research is limited, intermittent fasting schedules such as 16:8 have been shown to reduce the amount of androgens in both men and women.[1] Androgens are our growth and reproduction hormones, more readily found in men. In women, they are naturally produced in smaller amounts, but for some women, like those with PCOS, they can be in excess, causing irregularities in period cycles and problems with fertility. For women with PCOS or hyperandrogenism, intermittent fasting may prove to have benefits in terms of regulating cycles and improving fertility.  

In general, we recommend women to start slow. Starting with shorter fasting periods, like 12:12, or even just adding an hour to your regular overnight fast and working up to a longer window is a smart bet in the beginning.

If you haven’t started your fasting journey yet and are not quite sure how to get started, read our intermittent fasting for beginners guide to learn more about the different schedules. Then, take our SIMPLE quiz to find out which one might work best for you.

How does intermittent fasting affect your menstrual cycle?

Intermittent fasting during your menstrual cycle can be safe and beneficial, but to keep it that way, there are a few intermittent fasting mistakes to avoid. 

There isn’t much research on intermittent fasting and the menstrual cycle. We know that aggressive calorie restriction can lead to hormonal changes which can affect if and when Aunt Flo shows up.[2] Overly restricting calories through time restriction is no different. 

Our recommendation is that women not fast longer than 18 hours to ensure they’ve got enough time to get in all the nutrition they need unless their doctor has given them the OK to do so. While research is lacking, what we do have points to gentler fasting approaches having little adverse effect on menstruation.[1] 

Some of the most common intermittent fasting side effects, especially when getting started, look and feel like premenstrual (PMS) symptoms.

• hunger and cravings
• irritability
• headaches
• fatigue and sleep issues
• upset stomach

This suggests the best time to start fasting is not during your luteal phase (i.e., before the start of your next menstrual period) when PMS is in full swing.[3] Those days are hard enough!

Is intermittent fasting on your period safe?

If you’re wondering, “Can — or should — you fast while on your period? Is it safe to do so?” here’s the answer. In general, intermittent fasting on your period is safe, but there are some things to take into consideration. During your menstrual cycle, your body goes through many changes; therefore, its needs change. We’ll get into more detail on that later. 

Notice how your body responds to fasting as you go through your cycle. If you are noticing any changes in your cycle or an increase in PMS symptoms, your body may be telling you to dial it back a bit. To stay safe, listen to these signals and adjust as needed. 

Are there any health benefits to fasting while on your period?

Again, there isn’t much research on the health benefits of fasting while on your period. As we discussed above, women with PCOS seem to benefit most.

One large study found that those following an intermittent fasting plan had lower levels of anxiety and depression.[4] But we must take these results with a grain of salt, as more research is required before we can confidently claim this as a benefit for all people.

Menstrual cycle phases and intermittent fasting

The average cycle is about 28 days but can run shorter or longer.[5] When is the best time to fast during your menstrual cycle? Let’s look at the four phases to find out. 

Menstruation  (Days 1–5)

This begins at the first sign of bleeding or shedding of the uterine lining (aka your period). It’s when progesterone levels start to drop back down and can cause an increase in inflammation.[6] 

Due to the potential anti-inflammatory benefit of fasting in those with a higher weight [7], this phase could be the optimal time to increase your fasting hours (if you want to, of course) and focus on anti-inflammatory foods like green leafy veggies, nuts, berries, and sweet potatoes.[8] 

Follicular phase (Days 6–14)

Estrogen and follicle-stimulating hormone (FSH) rise, causing the uterine lining to thicken, and an egg begins to form in the ovary.[9] 

With estrogen comes higher energy levels and a mood boost.[10] This may be the ideal time to fast during your menstrual cycle. And, as insulin sensitivity is also at its best during this phase [11], it’s a good time to focus on high-fiber, complex carbohydrates like whole grains, beans, and fruits during your eating window. 

Ovulatory (~ Day 14)

Here, yet another hormone kicks in — luteinizing hormone (LH), which causes the now-fully-developed egg to be released.

Estrogen is now at its highest, and perhaps you’re feeling cute and frisky. The reason for that pep in your step: you are now at your most fertile. Perhaps you’re also feeling kinda “hot and bothered.” That’s due to your body temperature being higher, making hydration even more important. 

With insulin sensitivity still high [11], keep eating those B-vitamin-rich complex carbohydrates. You’ll need those B vitamins in the next phase when progesterone is queen, your mood drops, and PMS symptoms are looming.[12]

Luteal (Days 15–28) 

The released egg travels down the fallopian tube to the progesterone-prepared uterus for fertilization and attachment. 

This phase includes PMS (or premenstrual dysphoric disorder [PMDD] for some) and heightens your need for some TLC. Stress levels are high, hormones are shifting, inflammation is raging, and your body is more sensitive to all of it. 

Although fasting may help with inflammation for some [7], it can also add stress to a system that’s already under pressure.[13] This is a good time to take a break from fasting or at least dial it back to shorter fasts. 

Aim to minimize simple carbs like soda, cakes, and cookies to keep your blood sugar level. Continue to fill up on those antioxidant-rich foods (may we suggest dark chocolate covered almonds? You can thank us later) and leafy green vegetables, drink some peppermint tea, and get some snuggles in with your favorite person, animal, or comfy blanket. This is the time to treat yo’self!  

Intermittent fasting tips for women on their periods

1. Begin tracking your cycle if you aren’t already. Take note of any symptoms and changes in your mood or energy.

2. Take good care of yourself by taking our SIMPLE quiz. That way, when you’re ready to try fasting, you’re all set up with your intermittent fasting schedule and plenty of SIMPLE support. It’s here we can make sure you have plenty of healthy yet tasty dinner ideas, too. Check it out! 

3. Be flexible, and don’t be afraid to take a break or step back if your body asks you to. 

4. With period blood loss, your iron can run low.[14] Address this by eating more: 

• Red meat, fortified cereals, lentils, tofu, spinach, and dried fruit for added iron. Pair with vitamin C for better absorption, and avoid tea or coffee during that meal. 
• Fruit, especially citrus, bell peppers, and strawberries, for added vitamin C to help with iron absorption.

5. Be mindful of getting adequate sleep. Poor sleep can affect your mood any day, never mind when your hormones are in flux. Changes in when you eat (for instance, eating carbs too late in the evening or in too small of amounts [15]) can affect sleep quality, which in turn can affect hormone cycles.[16] 

When should women avoid intermittent fasting?

For the majority of your cycle, you can feel confident in fasting as usual, but in that luteal (PMS / self-care / treat yo’self) phase, we’d recommend you go more gently. Maybe shorten your fasts (or take a break completely) and give your body some extra love and nutrients like iron and antioxidant-rich foods. 

Other times to take a step back from intermittent fasting would be when:

• you notice heavier bleeding than usual
• you have a delayed or missed period (and there is no other cause)
• you notice a worsening of symptoms, especially headaches, fatigue, and anxiety

These may be signs that your body is in a stressed state and fasting is hurting, not helping. So, chat with your healthcare provider before jumping into anything.

Thinking more broadly, there are some things that mean intermittent fasting isn’t for you, whether you’re on your period or not. If you: 

• have a medical condition
• take prescription medications
• are extremely active
• are under the age of 18, or 80 years old or more
• are pregnant, breastfeeding, or trying to conceive
• have (or are at risk of having) an eating disorder or have a history of one
• have a Body Mass Index (BMI) < 18.5

avoid intermittent fasting unless you have the full support of your doctor.

SIMPLE’s expert opinion and final thoughts 

The female reproductive cycle is intricate and complex, and intermittent fasting is a personal decision. If you’ve been asking yourself, “Can — or should — I fast while on my period?” we’re confident you’ll find the answers here.  

Intermittent fasting is fully adaptable to your needs and lifestyle, and you can use that to your full advantage every time your period comes around. Fasting during menstruation is far from a no-no. 

So is it OK to fast on your period? Yes, so long as you stay aware of how both fasting and your period affect your body and adjust as needed. And if you do find you need to put fasting on pause while on your period, it needn’t derail your efforts. In fact, that may be part of your unique fasting rhythm. Find the rhythm that works for you by listening to your body and staying flexible.

Any time you get stuck, we’re here to help! Take our SIMPLE quiz to get hooked up with all the resources you need to fast as you’d like to, learn how to build strong habits, and practice eating healthfully. 

Frequently Asked Questions about intermittent fasting on your period

Does fasting make you bleed more on your period? 

It’s unclear if fasting makes you bleed more on your period. If you are noticing heavier or longer periods, stop fasting and seek medical advice (we recommend you do that before getting started with intermittent fasting in general, as well). 

Can I fast if my period is about to end?

Yes, theoretically, you can fast if your period is about to end. Remember, the menses and follicular phases are generally prime fasting time, but base your decisions on your individual response to fasting. If you are feeling particularly low energy or taking a little longer to bounce back, you may want to hold off for a couple more days.

Is brown blood still considered a period? 

Yes, brown blood is still considered a period and can be a normal part of it. However, if this is a change for you, check in with your doctor just to be sure. 

How many calories do I need to regain my period? 

How many calories you need to consume in order to regain your period will depend on a number of things, including your height, weight, and activity levels. We suggest working closely with your healthcare provider to regain your period and get personalized recommendations before making any significant lifestyle changes.

Is it harder to lose weight on your period? 

It can definitely seem harder to lose weight on your period. Hormonal shifts may cause bloating, cravings, and water-weight gain. One study of healthy, overweight premenopausal women showed that changing what and when you eat during your cycle can help you continue to lose weight [17], so don’t lose heart even if it seems your body is against you. If you’re feeling stuck, you might find some answers in our guide on why intermittent fasting is not working for you.

Written by Melissa Renae

Medically reviewed by Louise Bula, RD