In 2019, "intermittent fasting" was the most googled food-related topic globally, and it still ranks in the top three. Intermittent fasting continues to be a popular diet tool amongst men and women alike. From weight loss to increased mental clarity, fasting fans tote the benefits of fasting methods for various reasons.  

However, any diet or health trend impacts each person very differently. Regarding intermittent fasting, women may respond quite differently than men. Understanding how fasting affects female hormones is essential in creating an effective intermittent fasting strategy and a significant factor in deciding if fasting suits you as a woman.

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What is Intermittent Fasting?

Intermittent fasting is the practice of regularly switching between a timed period of eating and a timed period of avoiding eating. While many diets focus on what to eat, intermittent fasting is focused on when you eat. Intermittent fasting can be used with a variety of diets and nutritional approaches.

There are many different types of intermittent fasting, such as:

• ‍Time-restricted feeding: a form of fasting in which a person eats all of their food within a specific time frame each day. The most popular form is 16:8 intermittent fasting, which has an 8-hour eating window and a 16-hour fasting window.‍
• Alternate Day Fasting: an approach where individuals fast one day and then eat a regular diet the following day. ‍
• 5:2 Intermittent fasting: a weekly approach to intermittent fasting that has a person fast on two non-consecutive days each week; the two fasting days limit calories to about 25% of one's regular caloric intake (so food is not entirely avoided in this method).

There are also many other types of intermittent fasting. For example, fasting methods have been used to improve physiological function and insulin sensitivity, promote fat loss, and improve thinking and memory.

How Does Intermittent Fasting Affect Women's Hormones?

Intermittent fasting can impact women's hormones and can either be beneficial or potentially harmful - it's all about the frequency and duration of fasting and understanding that women need to fast in a way that supports their changing hormones.

Fasting can be a valuable part of a woman's health routine, and there's evidence of this value in areas such as cancer risk reduction, chronic pain, healing metabolic syndrome, treating PCOS, and supporting mental health.  

PCOS

One area that is being researched more and more is how intermittent fasting can impact PCOS. Intermittent fasting, particularly 16:8 time-restricted fasting, has shown favorable effects in several studies related to polycystic ovarian syndrome (PCOS). Fasting was shown to decrease levels of androgens, like testosterone, while improving insulin resistance and reducing body fat in women with certain types of PCOS. In some women, intermittent fasting may be therapeutic for hormone regulation.

Fasting may not always be beneficial, though. There are specific areas within women’s health where fasting may be doing more harm than good.  

Menstrual Cycle Regularity

Many benefits of intermittent fasting are due to how one's body adapts to perceived stress. Short-term stressors can be good for us, helping us to be able to better adapt to stress in the future. With prolonged stress (including fasting), the hypothalamus will "turn down" the production of reproductive hormones that are important for ovulation and a healthy menstrual cycle. So it's possible for fasting to be "too much" of a stressor in some women, stressing them enough to prevent healthy ovulation.

Another study looking at the effects of intermittent fasting on DHEA levels showed that fasting could lead to a decrease in DHEA in pre- and post-menopausal women. DHEA has many roles in the body, one of which is to stimulate egg production in premenopausal women, playing a role in fertility.  

If you're noticing changes in your period (or losing it altogether) while fasting, that's a sign that you may be overdoing it.

Thyroid Function

Studies suggest that thyroid function decreases with prolonged fasting, though the thyroid regains its function once fasting is stopped. Any long-term period of calorie restriction has the potential to slow thyroid function if it isn't balanced with periods of eating adequate calories. Hypothyroidism in women has been linked to fertility issues and potentially to a decrease in progesterone levels. For women, it's essential to ensure that intermittent fasting isn't causing a reduction of thyroid hormones, especially if she's trying to get pregnant.

Effects On Insulin And Blood Sugar In Women

One study showed that certain types of fasting (alternate-day fasting) negatively impacted the blood sugar response in non-obese women. This suggests that women may benefit from some types of fasting more than others and that women who are a healthy body weight may not experience the same benefits as women who are overweight or obese when it comes to blood sugar regulation.

How Female Hormones Affect Metabolism?

Estrogen plays a vital role in metabolism, impacting insulin sensitivity, cholesterol metabolism, hunger-satiety signaling, and maintaining nutrient balance. Healthy estrogen levels are essential for a healthy metabolism. As women go through menopause, they can experience symptoms related to decreasing metabolic health as their estrogen levels decline.  

Progesterone affects how women metabolize the three primary macronutrients: carbohydrates, fats, and proteins. Progesterone also can play a role in blood glucose regulation, influencing insulin sensitivity throughout the menstrual cycle.

Because estrogen and progesterone are constantly communicating with various other hormone systems (i.e., thyroid hormones, cortisol and the stress response, and inflammation pathways), it's easy to see how changes in hormone levels are continually impacting a woman's metabolic health.

Understanding how intermittent fasting affects female hormones can help you better gauge how your body would respond to different fasting methods. Working with a functional medicine practitioner to test and evaluate your hormone levels can ensure a safe approach to intermittent fasting and improving metabolic health.

How Intermittent Fasting Affects Women At Various Stages Of Life?

There are three major hormonal stages in a woman's life - premenopausal, perimenopausal, and postmenopausal. Each stage comes with its own hormonal changes. Women considering intermittent fasting should understand how their hormones may be affected by fasting to make the best decisions on the timing and frequency of a fasting method.

Premenopausal (Women Under 40 Years Old)

• Calorie restriction can negatively affect progesterone levels, the female hormone that peaks in the second half of the menstrual cycle. Avoiding longer fasts during days 21-28 of your cycle can help to keep your progesterone levels healthy.  
• Trying out intermittent fasting earlier in your cycle (days 1-15) will likely let you see how you might benefit from fasting, depending on your goals. Your hormone profile is better suited to handle stressors like fasting earlier in your cycle.
• Watch out for combining too many "health" stressors at once. For example, while intermittent fasting, intense workouts, and dietary approaches like a ketogenic diet may all have a time and place, combining all three long-term is likely to lead to hormonal havoc. These lifestyle options, especially all at once, may impact cortisol levels, which can affect hormones like insulin, estrogen, and progesterone.

Perimenopausal

• Women in their 40s and early 50s experience many shifting hormones as they move through perimenopause, and their cycle isn't entirely as predictable.
• As estrogen and progesterone levels start to decline, the body "hands off" sex hormone production to the adrenal glands, making perimenopausal women a little more sensitive to stress and shifting energy levels.
• Watch for signs and symptoms of low progesterone when fasting, such as spotting, insomnia, irritability, weight gain, or anxiety. A comprehensive female hormone panel can help you better understand what's happening with your hormones and how to time intermittent fasting methods to your unique physiology.

Postmenopausal

• After menopause, a woman's hormone levels are more stable than when she had a menstrual cycle (since she's making minimal hormones now), so the timing of intermittent fasting doesn't need to be as specific. It's a great time to try it out, though even postmenopausal women can benefit from taking "breaks" from intermittent fasting regularly.
• Intermittent fasting may help postmenopausal women experience improvements in body composition, insulin response, blood pressure, and lipid levels, all common health concerns for women in post-menopause.

Why Men And Women Respond Differently To Intermittent Fasting

While more inclusive studies need to be done to better understand the impacts of fasting on women, there are a few potential contributing reasons for the difference in response.

First, women have different hormone profiles than men, and their hormones are constantly in flux. While men have a hormone profile that is relatively similar daily, women's hormones - at least until after menopause - shift throughout their cycle. Their response to fasting differs depending on the day and specific part of their cycle.

Second, women may be more sensitive to changes in nutrient balance than men due to a molecule called kisspeptin. Kisspeptin controls an integral part of the reproductive pathway and is sensitive to hormones like insulin and leptin, which help us regulate hunger and satiety signaling. Women have higher levels of kisspeptin than men, which may influence the effect of fasting.

Third, women may respond differently to decreases in specific macronutrients, such as protein or carbohydrates. If women are not eating adequate protein for their body weight and activity levels, the body will sense that amino acids (the building blocks of protein) are low. If amino acids are too low, it can negatively impact estrogen binding and a hormone called IGF-1 (insulin-like growth factor 1). Both of these are important for thickening the lining of the uterus during the menstrual cycle; if the lining does not thicken, it can negatively impact fertility.

Specialty Lab Test That Help Determine If Intermittent Fasting is Affecting Your Patients Hormones

Comprehensive Female Hormone Panel

Evaluating female hormones can help you and your practitioner understand what is happening with your hormones so that you can structure the best intermittent fasting plan and assess if fasting is appropriate for you. Retesting periodically when fasting for long periods can help to see if you need to adjust your intermittent fasting schedule.

Fasting Blood Glucose

Fasting glucose measures your blood glucose after an overnight fast. A fasting blood sugar level of 99 mg/dL or lower is normal, 100 to 125 mg/dL indicates you have prediabetes, and 126 mg/dL or higher indicates diabetes.  

Fasting Insulin

Fasting insulin can be a helpful biomarker to evaluate, especially for women interested in using intermittent fasting methods to help treat insulin resistance.

Continuous Glucose Monitor

Using a continuous glucose monitor can help you keep track of your blood glucose levels while fasting and can help you make sure levels don't drop into an unhealthy range.

Comprehensive Stool Analysis

A comprehensive stool test can help a practitioner understand each patient's unique nutrient needs and any digestive support that may be helpful while trying intermittent fasting. Repeating a stool test periodically while practicing fasting methods can help evaluate nutrient needs and continue personalizing support as much as possible.

Should Women Intermittent Fast?

Women can use intermittent fasting as part of a healthy lifestyle - they just need to fast differently than men!

A few considerations for women who are fasting:

• If you experience changes in your menstrual cycle or lose your period, you may want to take a break from fasting and talk to your practitioner.
• For premenopausal women, fasting during the week leading up to your period may not be beneficial, whereas fasting in the first half of your cycle can confer health benefits like fat loss and improved metabolic health.
• Getting your hormones checked regularly while fasting is essential to make sure you're supporting healthy hormones
• Women who are trying to get pregnant or who are pregnant or breastfeeding should not use fasting methods and should discuss any dietary changes with their health practitioner.  
• Women who have a history of disordered eating should also avoid intermittent fasting, as it can be a trigger behavior.

Summary

Intermittent fasting can be a great health tool for women, though women should understand they need to approach fasting differently than men. As women move through different hormonal phases in life, their fasting approach also needs to change. Aligning a fasting schedule with your menstrual cycle is a good starting point to see if the benefits of fasting can work for you.

The most important thing is to make sure you can listen to your body cues and work alongside a practitioner to ensure you don't experience any adverse effects on your hormones from an intermittent fasting protocol.