Fasting for Health and Hormone Balance: What Women Need to Know

Fasting and ketogenic nutrition have gained great momentum in recent years, and for good reason: they offer powerful tools to improve metabolic flexibility, support longevity, and reduce the burden of chronic disease. As a doctor specializing in preventive and nutrition medicine and fasting, I want to emphasize an often-overlooked truth: not all fasting is created equal, and women in particular need to approach fasting with a nuanced, body-aware strategy.

In this article, I’ll explore the benefits and potential pitfalls of fasting, especially for women, and explain how the Fasting-Mimicking Diet (FMD) offers a gentle alternative with all the health benefits of fasting — and how to integrate it in a woman’s cycle without compromising well-being.

The Science Behind Fasting

Fasting is not simply “not eating” — and it is also not “starving.” It’s a highly orchestrated physiological process that shifts the body from glucose metabolism to fat burning, enabling deep cellular repair mechanisms like autophagy, reduced inflammation, and improved insulin sensitivity. Autophagy is the body’s cellular recycling system, where damaged or dysfunctional components are broken down and reused to maintain or even renew cellular health.

For myself, one of the most fascinating benefits of fasting — and one I see consistently in clinical practice — is its positive effect on brain function. When the body switches into fat-burning mode, it produces ketone bodies such as beta-hydroxybutyrate (BHB). These ketones are more than just fuel — they are signaling molecules that reduce inflammation and oxidative stress, promote mitochondrial function (cell energy), and regulate gene expression (turning on and off genes).

From a neurological perspective, ketones:

Provide a cleaner, more efficient energy source than glucose
Enhance the production of brain-derived neurotrophic factor (BDNF), which supports neuroplasticity and memory
Reduce oxidative stress and neuroinflammation
Support mitochondrial biogenesis in brain cells

Subjectively, many people report a striking sense of mental clarity, sharper focus, and improved concentration during fasting or when in ketosis. In the long term, this metabolic shift may offer preventive benefits against neurodegenerative diseases such as Alzheimer’s and Parkinson’s. Research increasingly supports the idea that ketones may help preserve cognitive resilience, especially as we age.

Therefore, a smart concept is combining fasting with a ketogenic diet, which may amplify metabolic benefits, as nutritional ketosis promotes fat oxidation and endogenous ketone production without the need for extended fasting periods.

Fasting and Female Physiology: A Delicate Balance

Yet, fasting is a natural stressor to the body. The stress of fasting — especially prolonged fasts — triggers hormonal pathways, including cortisol and adrenaline, which can backfire if the body is already stressed, undernourished, or hormonally imbalanced.

While both men and women benefit from fasting, female physiology — particularly related to the menstrual cycle, reproductive hormones, and metabolic regulation — requires special attention. Cyclical fluctuations in estrogen, progesterone and leptin influence insulin sensitivity, stress responses, and nutrient demands. Fasting — especially prolonged fasting — can disrupt this delicate rhythm if not adapted to a woman’s hormonal landscape.

Some signs that fasting may be too intense for a woman at a given time include:

Poor sleep
Mood swings
Irregular or missed periods
Hypoglycemia
Feeling cold, weak, or anxious

That’s why I recommend cyclical fasting and Fasting-Mimicking Diet (FMD) — gentle strategies that allow for metabolic benefits without overstressing the body.

The Fasting-Mimicking Diet (FMD)

One of the most exciting tools in modern fasting science is the Fasting-Mimicking Diet, originally developed by Dr. Valter Longo. This approach provides the body with minimal, precisely designed nutrients that do not interrupt the fasting-like state — allowing individuals to access many of the benefits of fasting without complete food deprivation.

As a fasting expert, I guide individuals into the fasting process with this method and especially recommend the FMD for:

Women sensitive to prolonged fasting
Individuals with lower BMI
Those new to fasting and concerned about energy crashes and starving
Individuals seeking metabolic or cognitive benefits with fewer risks

Clinical studies show that FMD enhances ketone production, supports weight loss, reduces blood pressure, and improves metabolic and inflammatory markers — all without the physical stress of complete fasting. Importantly, ketone production can be quite elevated, as healthy fats are included. This enhances mental clarity and mood regulation, making FMD particularly useful for women juggling hormonal balance and mental performance.

A Case Report: Missing Links for Smart Fasting

This case involves a woman following a fasting and feasting protocol tailored to different phases of the menstrual cycle. After a couple of days of fasting, she experienced weakness, poor sleep, and muscle pain during the night. The following morning, she awoke feeling lightheaded, and her blood glucose reading was 55 mg/dL (3.0 mmol/L). After eating a low-carb meal, she reported feeling much better, but was also uncertain whether fasting might negatively affect her health. She recalled reading research years ago suggesting that women shouldn’t fast because it could disrupt hormonal balance.

As a medical doctor specializing in preventive medicine, metabolic health, and fasting, I see this case as an important example — not of “too much fasting,” but of missing foundations that could have made the experience safer and more beneficial:

Symptomatic hypoglycemia (lightheadedness at 55 mg/dL): This reflects poor metabolic flexibility and delayed ketone production, possibly due to underlying insulin resistance. Without sufficient fat adaptation, the body struggles to maintain stable energy during a fast.
Poor sleep during fasting: Sleep disturbances are often related to elevated cortisol, one of the body’s stress hormones. As glucose and insulin levels fall, cortisol rises to stimulate gluconeogenesis and ensure adequate fuel, if ketone production is not yet increased. If cortisol remains elevated into the night, it can impair deep, restorative sleep.
Muscle pain at night: Likely caused by an electrolyte imbalance, particularly from sodium and magnesium loss during fasting. Without adequate electrolyte intake, symptoms like cramps and muscle aches may occur.
Quick recovery after eating: Her rapid improvement suggests that the meal provided enough glucose or protein (for gluconeogenesis), along with salt and fat to support ketone production and stabilize energy levels.
Lack of personalized support: Since this was likely her first experience with fasting, expert guidance or participating in a guided group setting would have provided valuable support — even though she fasted during a theoretically suitable phase of her cycle.
Gradual adaptation to fasting is essential to build metabolic resilience and reduce the risk of adverse effects.

What I Recommend Instead

For women who wish to benefit from fasting while respecting their hormonal and metabolic individuality, I recommend the following foundational principles:

Begin with metabolic preparation: Develop fat-adaptation first — through a ketogenic or low-carb diet, or time-restricted eating — before attempting prolonged fasts.
Track your menstrual cycle: Avoid extended fasts during the late luteal phase (about 10 days before bleeding begins), when progesterone is high and the body’s need for nourishment increases.
Use fasting-mimicking strategies (FMD) with awareness: FMD can offer many of the cellular benefits of fasting — such as autophagy and metabolic switching — with less abrupt energy restriction. It may be particularly useful in individuals with insulin resistance who are not yet ready for longer fasts. However, FMD still activates stress pathways and should not be used during hormonally sensitive phases (like the late luteal phase), when the female body requires more nutritional stability. Careful timing and adaptation remain key.
Prioritize electrolyte support: During any fast, especially beyond 24 hours, supplement sodium, potassium, and magnesium to support muscle, nerve, and sleep function.
Watch for red flags: Symptoms like fatigue, dizziness, hypoglycemia, or sleep disturbances signal the need to adapt your approach, and to get guidance.
Personalize your rhythm: No protocol fits every woman. Biofeedback, lab values, and daily energy are key indicators.
Support brain and hormone health with ketones: When fasting isn’t optimal, consider exogenous ketones to enhance mental clarity and resilience without placing extra demands on hormonal balance.

A new and increasingly accessible way for enhancing mental clarity, resilience, and other neurological benefits that ketones offer, even without entering a fasted state, are exogenous ketones. These compounds deliver ketones directly into the bloodstream, supporting brain energy metabolism, reducing oxidative stress, and stabilizing mood and cognition — without requiring food restriction. This can be particularly helpful for women navigating hormonally sensitive phases, such as the late luteal phase, or during times of emotional or physical stress, when fasting might place too much strain on the body. In these situations, the strategic use of exogenous ketones (perhaps with a gentle low carb approach) can provide metabolic and mental support, without disrupting hormonal balance.

Final Thoughts

Fasting offers profound health benefits, from improved metabolic markers to enhanced brain function and potential longevity effects. It is a powerful tool, and like any therapeutic intervention, fasting must be applied with care — especially in women, not only due to their hormonal rhythms but also because of the manifold social challenges they face, which are often accompanied by high stress levels.

Fasting does not have to mean pushing through fatigue, ignoring symptoms, or chasing strict numbers. It can be gentle, intentional, and sustainable. Tools like fasting-mimicking diets and exogenous ketones can be of great support — especially for women who seek to harmonize hormonal balance, mental performance, and healthy longevity.

Fasting — especially for women — should be tailored to physiology, life stage, and stress level.

The goal is not to fast longer or harder, but to fast smarter:

Respect your cycle
Build metabolic flexibility
Find the fasting method that fits your individual needs
Use supportive tools like exogenous ketones
Seek expert guidance and the support of a group — especially if you’re new to fasting

When applied wisely, fasting and ketogenic strategies can unlock not just metabolic health, but mental clarity, resilience, and long-term vitality.