Did you know that intermittent fasting in active females can help heal or completely wreck a woman? In this post, we’ll outline exactly who would benefit from intermittent fasting, when to perform it, and the right way to do it to make sure you get all of the benefits without any of the downsides.
Intermittent fasting has become one of the many popular diet trends in the last few years. Its promising metabolic and cardiovascular health effects have many people jumping on the bandwagon for the magical benefits! Especially in situations where you may be feeling “lost” in your health journey and looking for absolutely anything to jump-start your way to health, drastic measures that have resulted in seemingly overnight success for some individuals have become extremely enticing.
So what’s the problem? If there’s such great research to support fasting, shouldn’t we all be doing it?
If our ancestors fasted successfully year-round, shouldn’t we be equipt to do the same?
In some cases, yes, but not always. Let us show you all of the essential facts so you know exactly if you should be performing intermittent fasting and how to do it right.
What Sets Women and Intermittent Fasting Apart from Men
There are a lot of nuances to intermittent fasting for women due to the impact this style of eating can have on overall hormonal balance and stress in the body. Intermittent fasting for blood sugar regulation in individuals with type 2 diabetes looks different than intermittent fasting for female athletes and thus intermittent fasting and menstruation.
Some of the details you need to consider about fasting for women include its impact on hormones, your period, athletic performance, and more so that you can make an educated decision about the safety of fasting for YOU and YOUR body (not your best friend Sally!)
Listen, what works for one person, does not always work for another, and that’s ok!
But first, what is intermittent fasting? Let’s review some of the basics of fasting and some benefits before we dive into the nitty-gritty of intermittent fasting and women!
Interested in a free 3-Day Meal Plan for the Active Female to learn how to fix hormone imbalance, bloating, painful periods, and so much more? Download it for free now.
What is Intermittent Fasting?
Intermittent fasting is a pattern of eating where your daily calories are consumed during a specific window of time. Outside of that set window of time, you are not eating food or drinking calories.
So unlike most diets telling you what to eat, intermittent fasting is characterized by dictating when you eat. Similar to different styles of jeans, there are different styles of intermittent fasting. Different schedules dictate the different eating windows that a person would follow.
Schedules of Intermittent Fasting
There is research to support a variety of eating patterns that you may have heard about somebody doing or read about. Here are some of the most common.
12-hour fast. In a 12-hour fast, you eat within a 12-hour window and fast for a 12-hour window. For example, you consume your meals between 7 am and 7 pm, and then you do not eat between the hours of 7 pm and 7 am. Now, we would argue that this isn’t exactly any fancy form of intermittent fasting but rather just a natural pattern of eating that most individuals should follow. Nothing crazy here! It’s easy and still effective because it works with our natural circadian rhyme to eat when the sun is out and fast while we are sleeping.
The 16:8 method. This method is often the form of fasting people think of when they hear the term intermittent fasting or want to try it out. It’s a more popular approach to time-restricted feeding and it’s done by prolonging the overnight fast from 12 hours to 16 hours. You get 8 hours of your day to consume food and then do not consume food for 16 hours. This would look like eating between the hours of 12 pm to 8 pm and then fast between 8 pm to 12 pm. Essentially, this form of fasting has you skipping breakfast or maybe a mid-morning snack if you typically consume one.
This form of fasting can be problematic for females because of the within-day energy deficits.
Experts will argue that one can still consume all the food they need to maintain an equal energy balance of calories in, and calories out, but this may not be enough for active females. You very well could meet your calorie/nutrient needs by consuming more food between 12 pm and 8 pm, but it doesn’t change the fact that the body is in a catabolic state for 16 hours. The body senses the stress of these acute energy deficits, which have been correlated with menstrual dysfunction in elite endurance athletes.
The 5:2 method. In the 5:2 method, you’re not actually restricted to a certain time window for eating or not eating, rather the amount of calories is dictated. For two days of the week, you only consume 500 or fewer calories and then 5 days of the week you eat as you normally would, whatever normal is for you.
Essentially, you’re still getting yourself into a weekly calorie deficit! This will likely result in weight loss, go figure! But we would argue that achieving a calorie deficit (if that is appropriate for you) is possible without having to practically starve for several days.
24-hour fast. Some individuals will fast for a 24-hour period or essentially a full day. This can be done for a few days in a row or split up during the week.
**We think it’s pretty obvious here that an entire day (or multiple days) without energy coming in is likely to cause more harm than good in an active woman who has performance goals.
Positive Impact of Women and Intermittent Fasting
One of the many theories of why intermittent fasting shows improved health outcomes, besides getting people into a caloric deficit to lose weight is that fasting stresses our cells. With any stress response in the body, the body responds to the stress by improving its ability to cope with stress and potentially resist disease.
There are even situations where intermittent fasting in women can be used therapeutically to address metabolic health issues like type 2 diabetes, insulin resistance, and obesity, but this is used temporarily, strategically, and in the right candidate!
Other health impacts include:
- weight loss
- fat loss
- cognitive function
- Improved sleep
- inflammation reduction
While all these benefits seem appealing and cause for jumping headfirst into intermittent fasting, these effects are not often representing females and the impact of reproductive function, aka a women’s main vital sign, or studied in the female athletic population.
Studies on intermittent fasting in active females have not yielded as beneficial results.
Intermittent Fasting and Hormones
The question of “does intermittent fasting work for women?” can be rather complicated, because the hormonal impact on women is so variable. Women, in general, are significantly more sensitive to stress than males which is why women tend to see more negative health outcomes and female hormonal imbalances with intermittent fasting than men.
Here’s another thing to consider with fasting…
Often the argument is made that “our ancestors have been fasting since the beginning of time” with no long-term implications on their bodies, but can we really compare the nature of our society now to the nature of our ancestors?
We now live in the 21st century where everything is go, go, go. We sit on screens all day, and we value constant productivity, where how much we accomplish in one day is glorified over resting more. The average person is chronically burdened with stress in ways that our ancestors never did.
So, the overall impact of this single stressor (fasting) is vastly different nowadays when we consider how overflowed our stress buckets are!
If we were spending the majority of our days making homemade tortillas around the campfire, the stress of fasting would likely be more tolerable and beneficial to the female body.
How Does Intermittent Fasting Affect Females?
The crucial piece of information to understand regarding intermittent fasting for women is that intermittent fasting has primarily been researched in men. Actually, let’s be honest, MANY nutrition approaches, trends, and sports nutrition guidelines are formulated based on male research.
Women are said to be too difficult to study because of the unpredictability of the menstrual cycle and our associated hormonal fluctuations.
I mean…is it not obvious that BECAUSE of the hormonal fluctuations that impact most, if not all functions in the female body, we should deeply consider the utility of something like intermittent fasting in females and not generalize results studied in 50% of the population to 100% of the population?!
I don’t know… just a thought!
Male and female physiology is vastly different and nutrition approaches impact us differently often.
Intermittent Fasting and Cortisol
As we mentioned earlier, fasting is a “stress” to the body, which is going to impact cortisol. Cortisol is the body’s primary stress hormone. It is absolutely crucial to have robust levels of cortisol so our body can respond to stress, regulate blood sugar, support immunity, reduce inflammation, and aid in many other biological functions. However, too much or too little of this hormone does the opposite of what it is intended to do.
Our cortisol levels fluctuate throughout the day. Upon waking up, levels naturally rise and then gradually fall throughout the day. A situation that could cause cortisol to stay elevated in the morning and now fall naturally is low blood sugar.
Can eating carbohydrates lower cortisol?
Yes, you read that right, the way to naturally reduce cortisol is to eat carbohydrates within an hour of waking up, which goes against the recommendations of intermittent fasting for women.
If the brain is burning carbs/glucose for fuel for the sake of reproductive function signaling and production of estrogen, and those nutrients are not available (from fasting), the body secretes more cortisol to keep the body moving and functioning. It’s essentially serving as back-up to glucose and helping the body overcome the stressful tasks it’s required to do, like the 289374298 demands we have from the start of the day!
So, when cortisol becomes chronically elevated, what’s the issue now? The remaining hormones, which we will get into shortly, that are required to signal for reproduction get downregulated.
Think about it, the body isn’t going to willingly make space for a body in an environment that is unsuitable!
Impact of Intermittent Fasting and Menstruation
And now for the main event! Intermittent fasting and menstruation! As I have alluded to in this article, intermittent fasting can affect your monthly Aunt Flo, because fasting influences our hormonal signaling due to the perceived stress the body senses.
Short-term stress can be very beneficial for the body, such as what we see with exercise. Your 30 min HIIT class or lifting session stresses your muscles, cardiovascular system, and nervous system actually supports healthy levels of metabolic adaptation.
A 30-minute workout is great. However, a 30-minute HIIT session, which you’ve done on 5 hours of sleep, before a very stressful workday, and without any carbohydrate in your system day after day after day becomes a recipe for adrenal dysfunction aka a hormonal storm!
It’s because of the disruption in signaling from the top down. The hypothalamus, aka your brain, senses a threat from a lack of resources coming in (aka food), which disrupts the proper balancing of hormones and downregulates the production of hormones that allow for reproductive function to happen!
How Does Intermittent Fasting Impact Gonadotropin-Releasing Hormone?
Gonadotropin-Releasing Hormone otherwise known as GnRH, is a hormone in the brain that signals for luteinizing hormone (LH) and follicle-stimulating hormone (FSH). LH and FSH signal for the production of sex hormones, estrogen in particular.
Without proper levels of estrogen, ovulation does not occur. Without ovulation, we have negligible levels of progesterone.
So how does intermittent fasting affect GnRH?
GnRH is highly sensitive to stress. Intermittent fasting is stress to the body as we’ve hopefully emphasized at this point! Also, GnRH is regulated by a neuropeptide called kisspeptin, which is dependent on circulating carbohydrate levels.[4,5]
Think about it… low carbs = low output of GnRH. So when you’re going for an extended period of time in the first part of the day without any nutrients (carbs in particular) cortisol can remain elevated and GnRH signaling can be disrupted, making for downstream negative effects on menstruation and fertility. This can look like delayed ovulation, no ovulation, short menstrual cycles, infertility, and more!
Again, disruption of kisspeptin and GnRH has been shown to decrease output of estrogen, which can prevent ovulation from occurring, thus leading to low levels of progesterone. 
Don’t want to take our word for it? No problem, but how about the data?
Here are screenshots of one of our client’s hormone levels while practicing intermittent fasting that reveals the impact intermittent fasting can have on raising cortisol levels and subsequent low levels of the sex hormones estrogen and progesterone.
How Much Can I Fast Without It Affecting My Period?
As you may expect, there is no one-size-fits-all approach to any nutrition approach. Fasting included. Every female responds differently and can take on a different amount of stress without it impacting the menstrual cycle.
The extremely brief answer to how much I can fast without it affecting my period is that many women can likely perform intermittent fasting 1-3x/wk during times of low stress and less intense training.
This means that most women will not likely be able to fast every week or even every month as very very few of us have had the time, job, family life, or overall capacity to live a low-stress lifestyle week in and week out. It requires regular high-quality sleep, whole foods, and a moderately paced work or family schedule to be able to fast on a consistent basis. Here is free a checklist to help you determine when you should, or should not be fasting:
The more detailed and long answer to how much or how often you can fast without it having an effect on your period is that it is truly individualized.
One female may do a 16-hour fast every single day and be completely unscathed, while other may notice disturbances in their period after a few weeks.
As mentioned, short-term fasting may be helpful for weight loss in women who have insulin resistance, but even in these situations we often find that women gain the weight back easily if fasting and/or the calorie deficit is too low and done chronically.
Some women are not going to notice a direct impact on their cycle with a few days or weeks of fasting. There have even been studies looking at how a 72-hour fast impacted GnRH and LH signaling in women and found no effect on levels.
Most individuals can do something for a short amount of time that causes stress and the body will show resilience through that stressor because the things our body can do really are AMAZING! The issues is when a stressor is applied consistently over weeks to months that disruptions are likely seen. Additionally, highly active female athletes need to be aware that they may respond differently than others due to the nutritional demand their bodies have over non-active women.
The bottom line is, the way we know how fasting is affecting our body is by being in tune with our cycle and tracking it.
Tracking our menstrual cycle clues us into this important vital sign. It helps us see how our individual body is responding, versus what the media and research articles say should happen.
Even if you seem to have amazing results with intermittent fasting initially, tracking your cycle can be an effective way to spot changes in your menstrual cycle early on before the irregularities become too great.
How Do I Track My Menstrual Cycle
Stay tuned for an entire article about ins and outs of tracking your menstrual cycle, but here are a few tools to help you get started.
- Cycle charting app
I recommend Wild AI for female athletes who are highly active. However, other apps that may be usual for women include Flo and Glow to begin paying attention to how often your menstrual cycle is occurring as well as tracking the symptoms mentioned above.
- Basal Body Temperature Tracking Device
Some women like the old school pen and paper approach where a regular thermometer is used to take temperature readings every morning and then recorded on a paper chart; however, many women like to take the leg work out of it and rely on a fertility tracking device such as Tempdrop of the DaysyDay Fertility Tracker. These devices in various ways will take your basal body temperate and then have an app to which the readings sync with.
What Does a Healthy Menstrual Cycle Look Like?
If you’re interested in figuring how if you have a healthy menstrual cycle, download our free checklist which is shown below.
Checking all the following boxes would constitute a healthy menstrual cycle!
- Cycle begins every 25-35 days
- 4-7 days of bleeding
- Ovulation occurs between days 13-18 of cycle
- 10-16 day luteal phase (second half of the cycle after ovulation occurs)
- Minimal pain, discomfort, cramping before and during period
- Absence of heavy bleeding or clotting
- Minimal signs of PMS (a little is expected) including breast tenderness, mood shifts, fatigue, nausea, bloating/puffiness, sleep disturbances, headaches/migraines, etc.
- Period does not debilitate you for an entire week
- Performance in gym does not feel flat during period
If you can’t check off the boxes above and you’re intermittent fasting, it would be a good idea to reconsider this approach for you.
Intermittent Fasting and Menstruation for Active Females Guide
As you can now see, doing intermittent fasting can greatly impact menstruation in active females and can be another fuel to the fire to drive hormonal imbalance symptoms. So, it is absolutely crucial you listen to your body and consider if it is truly a good time to add an additional stressor on your body.
We would argue the negative implications that prolonged fasting has on stress hormones and reproductive function does not outweigh the potential benefits if your cycle is disrupted.
So, if you’re an active woman that wants to fast, consider doing the 16:8 method noted above, focus on doing it during times when you’re training is less intense, your sleep has been regular, and your overall stress levels are low.
An example of how this may be applied is after a distance runner competes in a marathon. When they’re a few weeks past their event and in a recovery phase with lower mileage, throwing in some intermittent fasting 1-2x/wk for a month or so before ramping mileage and training back up may have some significant benefits in boosting autophagy (cellular clean up and repair) which may help reduce long term injury.
Final Thoughts on Intermittent Fasting in Women
Much of the determination of if intermittent fasting is beneficial to you will depend on timing and closely measuring how your body responds. Listen to your body and focus on applying the added stress of intermittent fasting only if or when it is likely your body can easily accommodate the added stress (which for many of us may not be anytime soon!).
If you’re all interested in fixing the problems with your intermittent fasting or menstruation and want to dive deep into how to painlessly and quickly correct your hormonal health, you may want to consider working one-on-one with one of our dietitians (including me) to get to the root of your fatigue, painful or irregular periods, or sluggish performance.
We have all the tools to help get things moving in the right direction from showing you where to shop for healthy snacks that will actually taste good and how to prepare delicious healthy meals in 15 minutes or less using just 5 ingredients. We’ll even help you build a personalized shopping list so you don’t even have to think about what to buy on your next grocery trip. If you’re ready to get started on fixing your issues once and for all and fixing them fast, schedule a FREE 15-minute strategy call to get started.
Not ready to book a call? Try our free 3-Day Meal Plan for the Active Female which will show you exactly how to get going in the right direction for fixing your health now.