Fasting, Women, and Hormones

I wanted to take a moment to address how fasting affects women, especially women over the age of 40. I’ve heard conflicting opinions about how fasting isn’t safe for women because of the hormonal toll it takes, so I wanted to look into it further.

I’ve been reading everything I can on the subject of women, fasting, and hormones, and I’ll share with you what I’ve learned. Off the bat, I would recommend two excellent books on the subject: Fast Like a Girl by Mindy Pelz, and Intermittent Fasting Transformation by Cynthia Thurlow. Both address the specific considerations women face when we consider fasting, and both go into much more detail than I’ll venture into here.

Order Intermittent Fasting Transformation here

Also, for the ease of this discussion, “fasting” refers to intermittent fasting. That’s when you don’t eat for a period of time (usually 12-16 hours per day), and then you have an “eating window” of 8-12 hours per day. The point isn’t to reduce your daily calories, but rather to reduce the time during which they’re consumed. Benefits of fasting can include weight loss, fat burning, metabolic flexibility, improved gut health, decreased inflammation, and many others.

So to set the stage, while everyone has a 24-hour circadian cycle, females have to consider our hormone balance throughout the menstrual cycle. To complicate things further, some of us have a menstrual cycle, some are on hormonal contraceptives, others are in perimenopause (which happens several years before a woman’s last menstrual cycle, usually starting at age 40-44), and yet others are going through – or have gone through – menopause. So there’s a lot of variation to consider!

Order Fast Like a Girl here

Regardless of which category you fit into, the point is that fasting isn’t necessarily bad for women – it just has to be done correctly. In fact, it can help alleviate many of the hormonally-driven problems that women face. We just have to be cognizant of when we should fast, and when we shouldn’t. Fasting without respect for my hormones is probably why fasts made me feel so terrible before I learned how to do it properly.

The theory that fasting is bad for women revolves around the stress hormone cortisol. Fasting is a hormetic stress on the body. Hormesis means that something stresses you out in the short-term but makes you stronger in the long-term. Exercise is a great example. Anyhow, hormetic stressors cause the release of the stress hormone cortisol, and too much cortisol is bad for you. It’s particularly bad for women because it can signal to your body that you don’t have the resources to carry a child. And this will put the brakes on your normal, healthy sex hormones like estrogen and progesterone, causing you to lose your period. This is especially true if you are already lean, so it’s necessary to approach fasting with caution.

But how much cortisol is too much? How much makes you stronger, and how much is detrimental? The answer is: it depends. (This is my least favorite answer.)

First, it depends if you’re cycling. If you are, then it’s probably best not to fast every day, or you could be at risk of losing your period. Again, this is particularly true if you don’t have much fat to lose. It’s also important to consider the timing of your fasts across your menstrual cycle. The first 10 days of your cycle (day 1 is your first day of bleeding) is the best time to fast because your body is focused on making estrogen. Estrogen isn’t actually affected as much by cortisol, but it suffers when your glucose and insulin are high, such as when you eat a high-carbohydrate diet. So if you want to fast and/or eat a low-carb diet, you’ll feel best if you time it for days 1-10. It’s even safe for the first three weeks of your cycle, just don’t overdo it.

The worst time to fast is the week before your period. This is the time when the hormone progesterone is increasing. Unlike estrogen, progesterone hates the increases in cortisol caused by fasting. If you spike your cortisol too much, you run the risk of tanking your progesterone. This can cause spotting, missed cycles, irritability, and trouble sleeping. Instead, progesterone thrives with a higher-carb diet, so this is the time to add in natural sources of carbohydrates, such as potatoes, and to avoid things like excess stress and a low-carb diet.

If you’re going through perimenopause, fasting can really shine for you. This is because many women in perimenopause are “estrogen dominant.” This means that even though both estrogen and progesterone decline as we age, progesterone declines more, leaving us with a relative excess of estrogen. This can cause hot flashes, irregular bleeding, mood changes, weight gain, and decreased libido. Since fasting can help us detoxify estrogen (by microbiome changes and cellular cleanup), it can actually improve our symptoms. Just avoid fasting the week before your period and when you’re under a lot of stress.

Finally, menopause. This is probably the stage when the benefits of intermittent fasting for women are greatest. Without the need to time fasting to a hormonal cycle, you can achieve more of its benefits like more energy, improved weight control, less inflammation, and improved insulin sensitivity. Some experts recommend varying the lengths and days of your fasts, and both of the books below have programs that will walk you through a fasting regimen.

I hope that helped you understand that fasting isn’t necessarily bad for women, but we do have to consider our hormones. Again, here are the two books from which I’ve sourced this information if you’d like to learn more.

Fast Like a Girl – Dr. Mindy Pelz

Intermittent Fasting Transformation – Cynthia Turlow, NP