Introduction
Intermittent fasting (IF) has become one of the most popular dietary trends in recent years.Praised for its potential to promote weight loss and improve metabolic health, IF alternates between periods of eating and fasting. Yet, as women increasingly adopt this eating pattern, researchers have raised an important question: How does intermittent fasting affect menstrual cycle regularity and reproductive health?
The menstrual cycle is governed by a delicate hormonal network known as the hypothalamic- pituitary-ovarian (HPO) axis, which regulates hormones such as estrogen, progesterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) (Sallis et al., 2021). Any disruption to this system—whether through diet, stress, or illness—can lead to irregular cycles, anovulation, or conditions such as polycystic ovary syndrome (PCOS) (Harvie et al., 2010).
The Science Behind Fasting and Hormones
Emerging evidence suggests that intermittent fasting can influence reproductive hormones. In a review of human trials, Cienfuegos et al. (2022) found that fasting reduced androgen levels and increased sex hormone–binding globulin (SHBG), particularly in women with obesity. Similarly, Kim et al. (2021) demonstrated that fasting alters circadian patterns of hormone secretion, highlighting the complex relationship between diet timing and endocrine function. For women with PCOS, who often struggle with hormonal imbalance and irregular periods, IF may be beneficial. Li et al. (2021) reported that an eight-hour time-restricted feeding (TRF) schedule improved menstrual regularity and metabolic health among women with anovulatory PCOS. However, other studies caution that fasting can also disrupt energy balance and GnRH (gonadotropin-releasing hormone) pulsatility, potentially worsening menstrual irregularities when energy intake becomes too restricted (Kalam et al., 2022).
Mixed Outcomes: Not One-Size-Fits-All
While some research points to hormonal improvements, others find minimal or even adverse effects. Kalam et al. (2022) observed little change in sex hormone levels among both pre- and postmenopausal women following TRF, suggesting that age, metabolic status, and baseline hormone levels all influence how fasting affects the body.
Beyond hormone balance, IF has also been investigated for its effects on premenstrual syndrome (PMS). Hooshiar et al. (2023, 2024) found that alternate-day fasting (ADF) significantly reducedPMS symptoms and improved quality of life in women with overweight or obesity. This indicates that fasting may offer mood- and symptom-related benefits independent of menstrual timing.
Fasting Versus Other Diets
Comparative studies show that intermittent fasting may perform as well as, or better than, traditional calorie-restricted diets. Harvie et al. (2010) found that intermittent energy restriction improved weight loss and reproductive hormone profiles in overweight women. Meanwhile, Jakubowicz et al. (2013) discovered that meal timing—especially earlier eating windows—plays a crucial role in insulin sensitivity and androgen levels among women with PCOS. These findings suggest that when one eats may be just as important as what one eats.
Where Research Stands Today
The overall evidence remains mixed. Some women may experience more regular menstrual cycles and improved hormonal balance with IF, while others may face disruptions, particularly if fasting is prolonged or extreme. The diversity in fasting protocols, participant populations, and study durations makes it difficult to generalize findings (Gabel et al., 2018). Until long-term randomized controlled trials are completed, healthcare professionals recommend individualized dietary approaches. Women should consider factors such as body weight, activity level, and reproductive goals before starting any fasting regimen. Consulting with a healthcare provider or registered dietitian can help ensure that fasting supports—not harms—hormonal and menstrual health.
Conclusion
Intermittent fasting offers promising benefits for metabolic and hormonal regulation, particularly in women with PCOS or obesity. However, it is not a universal solution. Individual variability in response underscores the importance of personalized nutrition and medical guidance. As scientific understanding grows, future research must explore the long-term safety and reproductive consequences of intermittent fasting in diverse populations.
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