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Fasting & Your Menstrual Cycle

Oct 19, 2022 | Inflammation & Autoimmune Disease

Women have special needs when it comes to fasting, especially when they’re dealing with the menstrual cycle. Changes to our delicate hormonal balance can cause a number of issues for us. It’s important to understand why women need to be particularly careful with calorie restriction during our cycle and how to optimize fasting while menstruating.

Phases of the Menstrual Cycle

Before we dive in, let’s first talk about the phases of the menstrual cycle. We can break this down into four distinct phases.

  1. Phase one: menstruation.  This is when you’re actually bleeding and having an active period.  During this time, your body is shedding the uterine lining. It usually lasts around five to six days, and estrogen and progesterone levels are at their lowest.
  2. Phase two: proliferative phase. This phase starts when your period ends, and goes until ovulation. For most people, this is around day six to day 14. Your uterine lining is building back up again and estrogen levels are on the rise. Also, phase one and phase two are known as the follicular phase.
  3. Phase three: ovulation. This is when the egg leaves the ovary and you ovulate.  Estrogen is rising up until this point and signals the brain to release the luteinizing hormone (LH). LH triggers the release of your egg. After the egg is released. estrogen levels start to drop. Ovulation usually happens usually around day 14, but this can vary greatly depending on your cycle.
  4. Phase four: secretory or luteal phase. This is from ovulation to the start of your next period. During this phase, progesterone rises up until the next period starts. Then both progesterone and estrogen drop.

Why Does Fasting Interfere With Your Menstrual Cycle?

Fasting can trigger both stress and hormone imbalances, both of which can be detrimental to your menstrual cycle. The caveat here is that there’s very little research on the effects of fasting on women.


In a stress response your hypothalamus, pituitary, and adrenal (HPA) axis is activated.  Stress signals the release of corticotropin-releasing (CRH) which has a negative impact on regulating the Gonadotrophin-releasing hormone (GnRH). Additionally, CRH imbalances suppress reproductive function during stress. The other thing that CRH does is it stimulates two other hormones: the adrenal corticotropin hormone (ACTH) and cortisol. Cortisol is important here because cortisol actually suppresses the release of LH, which triggers ovulation. It can also alter the hormonal balance which can affect your menstrual cycle.


Intermittent fasting can also decrease estrogen. This happens because of a hormone called kisspeptin. Kisspeptin stimulates the production of LH and your follicle-stimulating hormone ( FSH).  Fasting can cause kisspeptin to decline, which can lower your estrogen levels overall. Lower estrogen levels can negatively affect your menstrual cycle. Lower estrogen levels are also tied to amenorrhea and infertility. In addition, estrogen levels also start to decline the week before your period starts. The decline in estrogen can be very stressful on your body and can trigger your cortisol levels to rise even more. That being said, your menstrual cycle can be stressful for the body in and of itself, and you’re just adding more fuel to the fire by fasting with declining estrogen levels.

How Do You Fast Safely?

Fasting according to your menstrual cycle can help keep your hormones balanced and keep your cycle regular. Again, everyone is different so go by how you feel about this. This is how you should try to fast to be in sync with your menstrual cycle.

During phase one of your menstrual cycle, it’s advisable to include fasting.  Start doing an overnight fast somewhere between 12 to 14 hours, beginning around day three of your period. 

During phase two of your cycle (the proliferative phase), which is around day six or seven to day 14, you can push your fast longer if you feel up to it.  This is usually when you have the most energy. Doing high-intensity exercises during this time and during the menstrual phase is allowed. Insulin sensitivity is optimal during these two weeks, you can eat more carbohydrates to fuel your workouts.

Phase three (the ovulatory phase) is usually when your body temperature rises. Push your fasting back a bit and reduce your exercise intensity. Focus more on proteins and fewer carbohydrates as insulin sensitivity starts to decline.

Phase four is your luteal phase after ovulation and right before menstruation. This is the time to really focus on self-care. Take the intense movement down and hold off on fasting. Your insulin resistance is much lower, so be careful about eating simple carbohydrates such as chocolate and sugar, which are usually what we crave during this time.

Hopefully this information will encourage you to be mindful when you try fasting. Again, not every woman will have a negative reaction to fasting. Some women’s bodies are completely able to tolerate fasting and truly thrive doing it. The bottom line is to listen to your body. Try fasting but be flexible with it. It’s not an all-or-nothing practice.

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