Women’s bodies undergo unique hormonal fluctuations throughout the menstrual cycle. Tailoring intermittent fasting to align with the menstrual cycle/infradian rhythm may help reduce the negative consequences of intermittent fasting on the menstrual cycle (read more about intermittent fasting and women’s hormones here). Before continuing with the article its important to state that there is very little, if any evidence that I am aware of conducted on tailoring intermittent fasting to the menstrual cycle. Much of the available information is based on conclusions of what we already know about female reproductive hormones. For example we know that estrogen is an insulin sensitiser and involved in appetite suppression and we know that progesterone promotes an increase in appetite. The progesterone phase is more likely to lean towards insulin resistance. Direct experiments on intermittent fasting at different parts of the cycle are very rare. I have linked what I could find at the bottom of this article.
Understanding the Menstrual Cycle and Hormonal Fluctuations
The menstrual cycle consists of four main phases but can broadly be categorised into the follicular phase (the first half) and the luteal phase (the second half). The cycle begins with menstruation, marking the first day of the follicular phase, which is primarily influenced by estrogen. As the cycle progresses, estrogen levels rise, leading up to ovulation, which occurs around the middle of the cycle. The follicular phase is variable in length and does not stay the same every month. Stress in the follicular phase can delay ovulation by means of delaying or interfering with the LH surge. After ovulation, the luteal phase follows, during which progesterone becomes the dominant hormone. The luteal phase is fixed and even though stress in the luteal phase can make hormonal symptoms considerably worse, it can not really affect the timing of the next period or ovulation. Under prolonged stress the luteal phase can become shortened (luteal phase defect) but this in itself is likely still a problem with ovulation quality and not the luteal phase itself (1). You can read more about understanding the menstrual cycle here. Because intermittent fasting is a considerable source of stress (because it can raise the hormone cortisol) it may have consequences on the menstrual cycle. Unfortunately, generalised lack of knowledge over the proper functioning of the menstrual cycle has led to recommendations for fasting that do not work for every woman.
Fasting in the Follicular Phase: Embrace Longer Fasting Windows
During the follicular phase (encompassing both the menstrual, follicular and ovulatory phase), the general recommendation is to embrace longer fasting windows. This is because estrogen levels are rising, and this hormonal environment usually supports the body’s response to fasting. Estrogen plays a role in insulin sensitivity, meaning cells respond better to insulin, and the body can use stored fat for energy more efficiently. Estrogen is also a natural appetite suppressant, making it easier and safer to avoid food during times when estrogen is high. As a result it is theorised that fasting can be extended to longer windows during the follicular phase. Some experts recommend anything from a 16 hour fast to fasting for 24 hours or more on certain days. The idea of switching up the fast is also promoted during this phase.
Longer fasting periods in the follicular phase may potentially support the detoxification and elimination of estrogen. During fasting periods, the body initiates cellular repair processes, promoting detoxification and renewal. This cellular rejuvenation can be especially beneficial for the liver and gut. By promoting liver function through intermittent fasting, the body can more effectively clear excess estrogen, potentially reducing the risk of hormonal imbalances associated with estrogen dominance. It is important to note that this is only beneficial for women who have a tendency to estrogen dominance, are insulin resistant, overweight and /or suffer with PCOS. Otherwise healthy weight women, may notice a worsening of hormone balance with fasting in the follicular phase. Read my article about the hormones affected by intermittent fasting here.
While intermittent fasting may somewhat support estrogen elimination during the follicular phase, excessively restrictive fasting or calorie restriction during the follicular phase may actually interfere with ovulation because it impacts the secretion of Lutenizing hormone (LH). Lutenizing hormone is the hormone responsible for triggering ovulation. The follicular phase is often seen as a time of increased resilience to stress, but this is only partially true. It is true that estrogen may help the body become more tolerant of mental and emotional stress for some women but in reality, the length and timing of the follicular phase is by nature very sensitive to stress. Of the very few scientific studies conducted directly on the impact of IF on the menstrual cycle on healthy women, the experiment showed a delay in LH secretion when IF occurred in the follicular phase (4). This lead to a delay in ovulation and longer menstrual cycles. Over time, excessive fasting/calorie restriction in the follicular phase can lower GnRh hormone which leads to low estrogen levels. This can in turn led to symptoms such as vaginal dryness, night sweats, hot flashes, depression/anxiety, long cycles and potential implications for fertility. For women with this hormonal profile, aggressive intermittent fasting during the follicular phase is not advised. Instead women should work on sufficient calories, good blood sugar control and a gentle form of time restricted eating emphasising an overnight fast of around 12-13 hours. One study found that a shorter overnight fast of around 12 hours in both the follicular and luteal phase was beneficial in LOWERING cortisol and calming the nervous system as opposed to to raising stress hormones (2). Sample size for this study was very small so much more research is needed.
Fasting in the Luteal Phase: Embrace Shorter Fasting Windows
As the body prepares for potential pregnancy during the luteal phase, progesterone levels rise, which can lead to increased appetite and calorie needs. During the luteal phase up to 300 extra calories are needed. During the luteal phase, especially the late luteal phase (the week before the period is expected) its advised to consider shortening the fasting window to avoid potential stress on the body. Maintaining a balanced calorie intake during the luteal phase is particularly important because the body requires additional energy to support the potential implantation of a fertilised egg as well as supporting increased caloric needs and blood sugar changes during this time. Restrictive fasting protocols during this phase may lead to increased stress levels and increase symptoms of PMS, period pain, fatigue and blood sugar imbalances. Most recommendations involve not fasting in the luteal phase and lowering physical activity to help support energy needs.
Concerns and Considerations
While aligning eating and fasting windows to the menstrual cycle and infradian rhythm can potentially mitigate some of the negative consequences of intermittent fasting for some women, there are still some concerns about the sustainability of intermittent fasting longer term.
Misalignment with the Circadian Rhythm:
The circadian rhythm is the body’s internal clock that regulates various physiological processes, including sleep-wake cycles, hormone production, and metabolism. Disruptions to this delicate rhythm can have adverse effects on overall health, including menstrual health. Irregular eating patterns and fasting windows may confuse the body’s internal clock, leading to sleep disturbances and hormonal imbalances. To mitigate this concern, it’s better to establish a consistent fasting schedule that aligns with the body’s natural rhythms. Avoid abrupt changes to fasting and eating windows, and consider practicing intermittent fasting during daylight hours when the body is naturally more alert and metabolically active. However this type of fasting, while gentle and supportive of hormonal balance and ideal for general health and longevity isn’t necessarily beneficial for rapid weight loss and unfortunately not widely promoted.
Impact on the Microbiome Clock:
The microbiome clock refers to the daily oscillations in the gut microbiome’s composition and function. The microbiome and digestive system as a whole learns to expect food intake at certain times of the day. Switching up fasting routines with the menstrual cycle and aggressively fasting in the follicular phase may lead to digestive imbalances and symptoms. This can have implications for gut health, nutrient absorption, and ultimately hormone balance. Digestive health and regularity is dependant on maintaining a consistent eating schedule and including a variety of fibre-rich plant foods in the diet.
A personal note
As a fertility awareness method instructor, I care a great deal about the menstrual cycle and teaching women to understand and appreciate their cycle. For this reason, I am concerned that much of the information about aligning intermittent fasting with the menstrual cycle is not very well supported by evidence and can not be applied to women across the board. From the research, I believe there is ample evidence supporting a prolonged period of time in-between meals, often the time needed for benefits is not as excessive as people believe. Aggressive intermittent fasting that requires constant change to stimulate the metabolism will likely have detrimental effects in the long run, even if it is only done in the follicular phase. From the limited research (and anecdotal research) currently available it is also obvious that overweight women with excess estrogen, insulin resistance and excess androgens are more likely to benefit from intermittent fasting in the follicular phase (6)(8). If you are a woman with this hormonal type, you may wish to experiment with intermittent fasting that is aligned with the menstrual cycle, however, monitor your body and adjust accordingly if the level of stress associated with intermittent fasting begins to show negative effects. Otherwise healthy weight women who wish to engage in intermittent fasting for various reasons might be disrupting the delicate balance of hormones that regulate ovulation.
I would not personally recommend extending fasting periods in the first half of the cycle, though it is thought to be safer to do so during that time. Although safer for overweight women with an androgenic profile, I would still caution the type of intermittent fasting performed and generally not advise aggressive fasting as this is not supportive for metabolism long term. For all women, changes in meal timing throughout the day leads to digestive confusion and circadian rhythm confusion. Instead women can simply adjust calorie needs between the follicular and menstrual phases while maintaining a gentle and sustainable time restricted eating approach long term. Read my article on time restricted eating here.
References:
2.Ohara, K., Okita, Y., Kouda, K., Mase, T., Miyawaki, C., & Nakamura, H. (2015). Cardiovascular response to short-term fasting in menstrual phases in young women: an observational study. BMC women’s health, 15, 67. https://doi.org/10.1186/s12905-015-0224-z
3.Kim, B. H., Joo, Y., Kim, M. S., Choe, H. K., Tong, Q., & Kwon, O. (2021). Effects of Intermittent Fasting on the Circulating Levels and Circadian Rhythms of Hormones. Endocrinology and metabolism (Seoul, Korea), 36(4), 745–756. https://doi.org/10.3803/EnM.2021.405
4.Berga, S. L., Loucks, T. L., & Cameron, J. L. (2001). Endocrine and chronobiological effects of fasting in women. Fertility and sterility, 75(5), 926–932. https://doi.org/10.1016/s0015-0282(01)01686-7
5.Olson, B. R., Cartledge, T., Sebring, N., Defensor, R., & Nieman, L. (1995). Short-term fasting affects luteinizing hormone secretory dynamics but not reproductive function in normal-weight sedentary women. The Journal of clinical endocrinology and metabolism, 80(4), 1187–1193. https://pubmed.ncbi.nlm.nih.gov/7714088/ https://doi.org/10.1210/jcem.80.4.7714088
6.Fagundes, G. B. P., Tibães, J. R. B., Silva, M. L., Braga, M. M., Silveira, A. L. M., Teixeira, A. L., & Ferreira, A. V. M. (2023). Metabolic and behavioral effects of time-restricted eating in women with overweight or obesity: Preliminary findings from a randomized study. Nutrition (Burbank, Los Angeles County, Calif.), 107, 111909.
7.Kalam, F., Akasheh, R. T., Cienfuegos, S., Ankireddy, A., Gabel, K., Ezpeleta, M., Lin, S., Tamatam, C. M., Reddy, S. P., Spring, B., Khan, S. A., & Varady, K. A. (2023). Effect of time-restricted eating on sex hormone levels in premenopausal and postmenopausal females. Obesity (Silver Spring, Md.), 31 Suppl 1(Suppl 1), 57–62. https://doi.org/10.1002/oby.23562
8.Li, C., Xing, C., Zhang, J., Zhao, H., Shi, W., & He, B. (2021). Eight-hour time-restricted feeding improves endocrine and metabolic profiles in women with anovulatory polycystic ovary syndrome. Journal of translational medicine, 19(1), 148. https://doi.org/10.1186/s12967-021-02817-2
