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Writer's pictureTanya Kurzbock

Intermittent Fasting and Your Hormone Cycle

Updated: Dec 27, 2022

Intermittent fasting is all the rage! But is it right for you? Does consistency pay off, or should IF have a more flexible approach? And why bother doing it at all?


This article will dive into all these questions and more.




Benefits of Intermittent Fasting

Intermittent Fasting (which will be called IF many times in this article) is hugely popular and can yield almost miraculous results in people. It has been used therapeutically to aid many chronic conditions such as Alzheimer's.


People report the following benefits;

  • Mental sharpness

  • Burning stored body fat

  • Chronic disease prevention

  • Overall health improvements

  • Easier weight loss

  • Optimised workout performance

  • Greater lean mass

  • Enhanced sleep

  • Stronger immune system

  • Stabilised blood glucose (anti-aging)

  • Boosted physical and mental energy


The mechanism of action behind these results comes from 2 things.

1 Hormetic stress. Fasting puts our body into a state of hormetic stress. This builds resilience and makes us stronger. It also builds metabolic flexibility. Metabolic flexibility means your body uses whatever fuel is available – dietary fat and stored fat, or glucose (sugar) and glycogen (sugar stores). In pre-industrial times, humans were metabolically flexible by necessity, but in our modern world, many of us have lost metabolic flexibility.

When we lose metabolic flexibility, our blood sugar system is not working so well, so missing meals causes issues such as hypoglycemia. People with poor metabolic flexibility tend to lose muscle before fat reserves when restricting calories and tend to have severe cravings at certain times, like before a period (for women).

The goal of building metabolic flexibility is to become 'fat adaptive', healthier, and prevent disease. Fat adaptive is where your body will use its fat stores for energy rather than muscle.

2. Reduces weekly calorie intake. The notion of calories in calories out with diet and exercise for weight loss is a very mechanistic approach. The thing that disrupts the simplicity of this statement is hormones. So people with hormone fluctuations may not lose weight with calorie restrictions from IF. This is the number one reason why menstruating women and perimenopausal women, have hit-and-miss results with IF. I'll talk more about this in a sec.




Types of Intermittent Fasting

There are many approaches to IF, and no real set rules per se.

The goal of this article is to learn how to identify your own body's needs, how to listen to its cues, and adopt the right form (if any) of IF according to your needs. Here are the 3 most "popular" forms of IF;


5:2 Diet

This is such a popular approach to IF, and works well for many people. The idea is to eat normally for five days (don’t count calories); then on the other two days eat 500 or 600 calories a day, for women and men, respectively.

I like to cycle this approach in with exercise on the morning after your fast day, and eating a large meal after the workout that contains 20 grams of protein. This is only appropriate for people with good metabolic flexibility.

Fasted exercise offers many health benefits, including enhanced autophagy, increased fat-burning, and anti-aging benefits. Through daily intermittent fasting and regular fasted exercise, you may increase your insulin sensitivity. It may lead to increased human growth hormone to help you burn fat, lose weight, and build muscle. Fasted exercise may help you to achieve your desired results faster and more effectively.


Time-Restricted Fasting (TRF)

With this type of IF, you choose an eating window every day, which should ideally leave a 14 to 16-hour fasting period. This means you eat your food in a 10 or 8 hour window respectively. The most common type of TRF is an eight-hour daily feeding window, known as the 16:8 diet.


You should eat as much food in the TRF window as you would any other day. However - I have seen many people slide here, and end up eating less and less, which resulted in a slower metabolism. The weight loss slowed to a halt, and rebound weight gain occurred.


You can combine both above approaches together as well - eg. on the 2 fast days, eat in an 8-hour window between 11 am and 7 pm.


Overnight Fasting

Just about everyone benefits from a 12-hour eating window and should aim for this every night. The 12 hours should fall overnight when you are asleep to allow your digestive system a rest. Also, do not eat within 3 hours of going to bed. It affects sleep by promoting cortisol, which interrupts melatonin production. It also disrupts natural detoxification and repair processes that occur only at night when melatonin is in the system telling the body to go to work healing.


Women and Intermittent Fasting

As mentioned earlier, fasting puts the body under hormetic stress. Therefore, women should be adapting their diet accordingly in order to get good results that don't affect energy, mood, and sleep.

Fasting is a hormetic stressor, so picking the right time to do it is essential.

Women in the peak of their fertile years with a menstrual cycle are most at risk of tipping the balance with fasting.

A woman's period is a 28- to 30-day intrinsic biorhythm. From the day she starts bleeding until right before ovulation, that is the follicular phase. This part of the cycle (and ovulation phase) is when fasting, exercising hard, and pushing oneself is best to do, as estrogen is nice as high.


When the cycle shifts to the luteal phase progesterone hormone rise. This is a time to slow down the intensity. The body also becomes a little more insulin-resistant. 5-7 days before the period, progesterone drops. In this time frame, women should not do more than 12 hours of fasting and should graze more. Adding in some starchy root vegetables into the diet may be helpful here too.


One reason women get such bad cravings right before their period is due to these hormone shifts, and her trying to maintain the same level of output as they did in the first half of her cycle. Instead, try slowing down in the 5 days before your period and just observe how differently you will feel.


When the bleed starts, hormones settle down again and fasting can be started again.

By honoring the menstrual cycle correctly, PMS symptoms quickly improve, and common gynecological issues such as endometriosis can be avoided.

Perimenopause and Fasting

This is a prickly subject to write about because of all the variable factors. By the time a woman reaches perimenopause (the 5 - 10 years preceding menopause), the state of her hormones varies greatly. Some women have auto-immune diseases, and others have hypothyroidism and others adrenal fatigue. Or a mix of all the hormone imbalances!

But regardless of that, the key term to remember is Hormetic Stressor. Just remember that fasting is a hormone stressor, and then factor that into your own situation. Do your hormones need more or less stress? Figuring that out may require some testing to allow you to make a better and more informed choice.

Some women will respond well adding stress to their bodies in the form of fasting. Others will not. Most women benefit from only fasting in the first half of their menstrual cycle. You will quickly know which one is which by assessing how you feel during and after your fast days.


Menopause and Fasting

Generally speaking, once a woman has not had a period (bleed) for 12 or months she is in menopause, and can start IF again at any time unless she feels worse for doing it.



Fasting with a Hysterectomy or "I don't get a period anymore"

If you don't experience a bleed, but are still hormonally active, picking the timing can be a bit tricky.

This occurs in a few situations, such as when a woman has had a hysterectomy but still has 1 or 2 of her ovaries. She may be using a contraception that skips her period. She may have been doing extreme fasting or exercise.

You may have some signs and symptoms of your hormone cycle, so do continue tracking these in a menstrual app. Signs such as larger or more tender breasts, changes in your mood - more irritability, food cravings (such as chocolate or sugar), more fluid retention, or adult acne around the chin. Keep a diary and see if these have a monthly pattern - that can help you see where you are at in your hormone cycles.

If you know where you are in your hormone cycle, avoid fasting - or any hormetic stressors - for 5 days before where your period would happen.

Regular hormone testing through a blood or saliva sample may be needed to get a true baseline of where you are at in your hormone journey.



Men and Intermittent Fasting

As most men do not have the same level of hormone fluctuation as women, they generally do really well with IF, lose weight fast, and gain all the benefits.

IF can assist in;

  • Reducing a 'beer belly'

  • Balancing blood sugars - unless insulin dependent.

  • Improving levels of a brain hormone called brain-derived neurotrophic factor (BDNF).

  • Lower blood pressure, LDL and total cholesterol, and inflammation.

  • Improve testosterone levels in obese men by boosting luteinizing hormone (LH) which is a precursor to testosterone production. [study]

  • Research has demonstrated that fasting helps to increase the secretion of growth hormone. This is of particular interest to bodybuilders who commonly use fasting to help them gain muscle mass.

How to Build Metabolic Flexibility

Taking into consideration everything I have mentioned about your hormones, if you decide to try using IF to build your metabolic flexibility, the key is to start slow, tune into your body, and let IT guide YOU.


People who are insulin resistant and not metabolically flexible tend to find it harder to go too long without eating. It’s best to start small and work up to longer ‘fasts’.


If your metabolic flexibility is very poor, then I must say that exercise is the best thing you can do to improve it. Exercise affects your hormones in a myriad of ways, and just focusing on diet alone is not enough for someone who has a tendency to be hormonally sluggish. If you have type 2 diabetes, (or leading up to it), hypothyroidism, stress and sleep issues, or chronic inflammation, exercising is the number 1 tip to start with. Finding the right exercise for you is another thing, and you should use discernment here as exercise is a hormetic stressor.


Exercise burns excess glycogen - essentially emptying your glycogen fuel tanks, which is the first step needed to build metabolic flexibility. Once glucose is depleted, your body can turn to fat for fuel.

It also improves insulin sensitivity, which improves fat adaptability.


Practice time-restricted eating (TRE). Pick a eating window that will work for you. I personally fluctuate this all the time. I workout in the morning on an empty stomach, and have a protein drink after the workout, then eat a meal when I get home. On non-gym days, I tend to fast until 11 am. Finding the right eating window for you takes some tuning in, but with persistence, you will find your own unique style. And it doesn't need to be locked in and rigid with a daily timesheet. Just like nature changes with her ebbs and flows, so should you.


No snacking. Insulin rises after every meal containing protein or carbs. The less insulin fluctuation throughout the day, the faster your metabolism can recover. Unless you’re snacking on pure “fat bombs."


Sleep. The body has an intricate connection between sleep and hormonal and metabolic processes. Sleep is key to minimising hunger and cravings. (if you have trouble here, check out my online course Overcome Insomnia)


The five markers of metabolic health include:

  1. Waist circumference

  2. Fasting blood sugar

  3. Prediabetic or Type 2 diabetic

  4. Pre-hypertension or hypertension

  5. Low HDL or high triglycerides.

If you need help improving any of these markers, book a free 15-minute call to chat with me on the phone about how I can help.


Thank you for taking the time to read my blog! If you are interested in science-based natural medicine information, challenges, healthy recipes, and inspiration to support your healthiest life, come join my community!

Once you are accepted to the group, you have access to my online course "Radical Wellness". I discuss diet and lifestyle tips for your path toward vitality and freedom, disease prevention, optimal health at all ages, naturally happy moods, and a healthy, functioning body. CLICK HERE






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