Intermittent fasting is a broad term that describes going for a period of time without eating. There are lots of different forms of intermittent fasting (16:8, 5:2, and OMAD, to name a few), but the intended benefits are generally the same across the board, including weight loss, increased energy, and improved mental clarity.
Although many people swear by intermittent fasting, there’s a gray area and conflicting opinions when it comes to whether or not intermittent fasting is safe for women.
Some experts argue that fasting can cause hormonal disruptions that can lead to mood swings and fertility challenges, while others say that it’s perfectly safe, as long as you’re listening to your body and doing it right. So, why the confusion? Let’s break down whether women should intermittent fast, and if so, how to do it healthfully.
Is intermittent fasting safe for women?
Double board-certified physician Amy Shah, M.D., who specializes in hormones, says it all boils down to your overall stress load. “Women are wired differently,” she explains, “They’re wired in a way that stressful situations to the body can cause negative effects on women’s hormonal cycles.”
The term “stress” often comes with a negative connotation, but it’s not all bad. There are a lot of health-promoting practices, like exercise and the keto diet, that put stress on your body.
If you’re managing your stress levels well, these practices prompt positive, healthy changes in your body. However, if you’re over-stressed, your body may not be able to handle any additional stressors. In this case, adding fasting, which Shah explains is “a hermetic stressor,” to the mix can cause negative hormonal changes, instead of the intended health benefits.
The bottom line is that every woman is different. Some women do great with intermittent fasting, but others are more sensitive to the stress it puts on the body. While there’s a lot of anecdotal evidence from women who have experienced everything from reduced cravings to better sleep to increased energy, there’s not enough scientific evidence to make definitive conclusions yet.
However, what we already know for sure is that there are certain groups of women who definitely shouldn’t fast. This includes anyone who:
- Is pregnant or breastfeeding
- Is underweight
- Has a history of disordered eating
- Is under a great deal of chronic stress
- Has other major medical issues, like diabetes or high blood pressure
How intermittent fasting can affect your hormones.
To understand why some experts are concerned about the safety of intermittent fasting for women, it’s helpful to have a little background on your hormones and how intermittent fasting can affect them.
Women produce large amounts of a compound called kisspeptin, which is a protein that’s highly involved in reproduction—and extremely sensitive to stressors, like fasting.
When kisspeptin is released, it activates a hormone called gonadotropin-releasing hormone, or GnRH. GnRH then stimulates the release of follicle-stimulating hormone (or FSH) and luteinizing hormone (or LH) from an area of the brain called the pituitary gland.
In women, LH triggers the ovaries to produce and release estradiol, a form of estrogen, and progesterone, two of the most critical hormones in reproduction. LH also signals your ovaries to release an egg during the ovulation period of your cycle. FSH stimulates the growth of follicles in the ovaries and also plays a role in estrogen production.
Some studies show that fasting decreases the production of kisspeptin, which, in turn, disrupts the production and release of estrogen and progesterone. In theory, this means that some women could experience hormonal disruptions that result in things like mood swings and missed or irregular periods. And in extreme cases, it could lead to fertility struggles.
But the problem is that most of the research on fasting’s negative effect on kisspeptin has been done on animals. One study that was done on lambs showed that short-term fasting could decrease the production of kisspeptin, which led to decreased levels of LH in the blood.
However, another study found that fasting had no effect on LH, FSH, estradiol, or progesterone levels during a woman’s mid-follicular phase—or the time between the first day of the menstrual cycle and ovulation.
Many experts caution that fasting may cause hormonal disruptions in women, but more research is needed to fully understand how fasting may affect hormones in humans.
Can fasting affect fertility?
Because fasting may negatively affect a woman’s hormones, there are related concerns about fertility. Some medical experts think that a woman’s body may see fasting as a danger of impending starvation. As a result of this, they think the body inhibits ovulation since there wouldn’t be enough nutrients to sustain a growing fetus.
However, there are other doctors, like Felice Gersh, M.D., who have opposing views. Gersh says, “Based on what we know now, my prediction is that short periods of fasting will actually enhance fertility.”
So, who’s right? Once again, the science isn’t totally clear—and most of the research has been done on animal models, instead of humans.
In one study, researchers looked at how three months of intermittent fasting affected female rats. They found that the rats not only lost 19% of their body weight, but they also had significant changes in their reproductive hormones. LH and kisspeptin levels went down, while estradiol levels went up.
However, another review looked at intermittent fasting in women with polycystic ovary syndrome, or PCOS—a condition that can lead to fertility challenges. The researchers hypothesized that intermittent fasting could actually improve fertility in women with PCOS by reducing levels of glucose, insulin, IGF-1, and IGFBP1.
According to the report, women with PCOS tend to have increased expression of IGF-1 and IGFBP1, two hormones that affect insulin production. When insulin levels get high, it triggers the body to make more androgen hormones, like testosterone, which makes it harder to get pregnant. On the other hand, when insulin levels go down, it can improve ovarian function.
Another study added on to this, concluding that short-term calorie restriction could actually increase LH levels in women with PCOS while simultaneously decreasing glucose, insulin, leptin, and testosterone.
Intermittent fasting & your period.
There’s also concern about whether you should fast during your period. But, according to Shah, you don’t have to avoid intermittent fasting when you’re menstruating; it’s the week before that matters.
Shah explains that the week leading up to your period is when you’re most sensitive to extra stress. That’s because your estrogen levels go down significantly, a change that also increases your sensitivity to cortisol, the main stress hormone. And since, according to Shah, women are hardwired to be more sensitive to external stressors, adding in extra stress, like intermittent fasting, can have negative effects on your body.
That doesn’t necessarily mean that you have to avoid intermittent fasting completely when you’re premenstrual, but it’s probably a good idea to scale back, at the very least. If you typically do a 16:8 fasting schedule, you may want to drop your fasting window down to 12 hours for the week. “And then the day 0 of the cycle to day 14 is kind of your green light to go a little harder on the fasting and the workouts,” says Shah.
Intermittent fasting during menopause.
Menopause, one of the biggest hormonal changes in a woman’s life, is another common concern. As you approach your 50s, the average age when menopause begins, estrogen and progesterone levels naturally go down. You also become less sensitive to insulin.
These hormonal changes can slow down your metabolism, making you more prone to weight gain. They can also cause other uncomfortable symptoms like mood changes, fatigue, brain fog, and psychological stress. This brings up questions about whether peri- and postmenopausal women should take up fasting.
Bhatia calls intermittent fasting an ideal tool to help get you through the discomfort of menopause, explaining, “If you’re struggling with weight gain, fatigue, and/or insulin resistance during menopause, you may want to give it a try.”
Of course, you don’t have to just take her word for it. Research shows that intermittent fasting can help improve insulin sensitivity and promote fat loss. In one specific animal study, researchers found that intermittent fasting helped improve insulin resistance in obese postmenopausal mice, even without calorie restriction.
Studies also show that intermittent fasting can help protect your brain from stress, diminish depression, and contribute to increased self-esteem and feelings of achievement.
Tips for women trying intermittent fasting.
If you do decide to try intermittent fasting, make sure you’re doing it smartly and safely. Here are some tips to get you started:
- Start with a smaller fasting window, and work your way up.
- Incorporate only two fasting days per week in the beginning.
- Avoid high-intensity exercise on fasting days.
- Listen to your body. If you feel weak, tired, or lose your period, stop fasting.
- Eat healthy, nutrient-dense foods during your feeding windows.
- Keep a journal to track how you feel.
The bottom line is every woman is different. Some women, especially those under extreme stress, are more sensitive to potential negative hormonal changes when fasting. On the other hand, there are some women who thrive with intermittent fasting.
One of the most effective ways to find out which camp you belong in is to try intermittent fasting for yourself and see how you feel. If you feel like something is off, it’s a good sign that your body isn’t reacting well to the additional stress. If you feel great, you can continue the course.
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