FMD and women’s health. Fasting and hormonal balance
Research on women and fasting reveals that the physiological and hormonal responses to fasting vary depending on the menstrual cycle phase and specific hormone interactions.
Understanding these nuances is crucial, especially when applying structured fasting protocols like the Fasting Mimicking Diet (FMD).
Menstrual cycle phases and fasting effects
Follicular Phase (Day 1 to ~10-12): this phase begins with menstruation and includes the rise of oestrogen while progesterone remains low.
Evidence shows women are generally more resilient to fasting during this phase.
Metabolic flexibility is higher, and fasting or the FMD tends to be better tolerated with fewer disruptions in reproductive hormones.
Studies indicate that fasting during this window avoids significant menstrual irregularities, supports metabolic benefits, and enhances cellular renewal processes triggered by fasting such as autophagy.
Luteal Phase (Post-ovulation to Menstruation): rising progesterone characterises this phase, which supports a preparation for potential pregnancy.
Research suggests fasting during the luteal phase may elevate cortisol (stress hormone), reduce leptin (critical for reproductive hormone regulation), and increase risk of menstrual disturbances or premenstrual symptoms.
Women might experience greater fatigue, mood changes, and metabolic stress, making this phase less optimal for intensive fasting like FMD.
Hormonal Interactions with Fasting
Oestrogen and Progesterone
Fasting can suppress the hypothalamic-pituitary-ovarian (HPO) axis, reducing secretion of gonadotropin-releasing hormone (GnRH), which can lower oestrogen and
progesterone production, particularly if fasting is prolonged or mistimed.
This suppression may lead to ovulatory irregularities or amenorrhea as an energy-conservation response.
Leptin, a hormone that signals energy sufficiency, falls during fasting.
Reduced leptin negatively impacts reproductive hormone release (LH, FSH), contributing to menstrual irregularity, especially if energy deficits continue.
Androgens (e.g., Testosterone): in women with conditions like polycystic ovary syndrome (PCOS), intermittent fasting or time-restricted eating has been shown to lower androgen markers such as testosterone and free androgen index, which often improves menstrual regularity and fertility.
In women without PCOS, the impact on androgens is less pronounced but fasting may still modestly reduce androgen levels.
Fasting, exercise, and stress
Fasting increases cortisol, especially when combined with intense exercise or when conducted during vulnerable hormonal phases like the luteal phase.
Elevated cortisol exacerbates menstrual disturbances and metabolic strain.
Thus, moderate rather than intense exercise during fasting, particularly FMD cycles, is advised to avoid excessive physiological stress.
Managing stress and avoiding simultaneous high physical stress during fasting periods supports hormone stability and overall health.
Specific Considerations for the Fasting Mimicking Diet (FMD) in Women
Women with menstrual irregularities, PCOS, or other endocrine disorders should consult healthcare professionals before beginning FMD to ensure personalized timing and support.
Monitoring menstrual patterns, energy levels, and stress symptoms during FMD is important to adjust timing or intensity as needed.
In summary, evidence strongly supports a cycle-aware approach to fasting in women.
The FMD’s benefits on metabolic health, such as reduced blood glucose, LDL cholesterol, visceral fat, and inflammatory markers, are maximised when scheduled during the follicular phase to protect reproductive hormone balance.
Awareness of hormonal fluctuations—especially oestrogen, progesterone, leptin, and androgens—and their interaction with fasting and exercise stress is essential for optimizing outcomes and minimising potential adverse effects.
References
1. Hooshiar SH, Yazdani A, Jafarnejad S. Effect of modified alternate day fasting diet on the severity of premenstrual syndrome and health-related quality of life in women with overweight or obesity: a trial study protocol. Trials. 2023; PMC10163452.
2. Hooshiar SH, Yazdani A, et al. Does an alternate-day modified fasting diet improve premenstrual syndrome severity and quality of life in obese women? Frontiers in Nutrition. 2024; 10:1298831.
3. Mishra A, et al. Fasting mimicking diet cycles versus a Mediterranean diet in overweight and obese individuals at risk for cardiovascular disease: comparative study. Nature Aging. 2023; article number s44324-023-00002-1.
4. Nair PMK, et al. Role of therapeutic fasting in women's health: An overview. Journal of Obstetrics and Gynaecology. 2016; PMC4960941.
5. Brandhorst S, et al. Fasting-mimicking diet causes hepatic and blood markers changes indicating reduced biological age and disease risk. Nature Communications. 2024; PMC article.
6. Clinical Trial: Effects of Fasting Mimicking Diet (FMD) in Women With Polycystic Ovary Syndrome. Clinicaltrial.be.
7. Micarelli A, et al. Chemosensory and cardiometabolic improvements after a 5-day fasting-mimicking diet in overweight/obese subjects. Scientific Reports. 2025.