Why Intermittent Fasting May Be Too Much For Your Period

The practice of intermittent fasting has been used as a therapeutic tool in Islamic and Buddhist cultures for centuries, and recently grew in popularity as a means to lose weight and improve disease outcomes.

In simple terms, intermittent fasting is an eating practice where an individual restricts the time period in which they eat. There are several different fasting patterns you can adopt: the 16:8 method of fasting for 16 hours and eating within an 8 hour window, the 5:2, five days of normal eating and two days of eating only 500 calories, or fasting for 24 hours one to two days a week.

Unfortunately most studies on intermittent fasting have used male subjects so we actually don’t know a whole lot about how this practice works for women.

In men, studies found that fasting for 12 to 24 hours boosted their metabolism by up to 14%, and increased levels of human growth hormone by 5-fold, improving muscle-building capacity. However, the same metabolism-boosting effect has not been seen in women. In fact, women’s metabolisms slow down to try and conserve energy. After 3 weeks of fasting women experienced worse blood sugar control, a factor that increases disease risk. Also, the rate at which women burned fat for fuel during periods of fasting plateaued as time went on, while men continued to see an increase.

So what kind of effect does all of this have on our menstrual cycles? Practicing prolonged (16 hours or longer) and daily fasting, especially if you’re at a healthy weight, can disrupt your hormones and cycle because your body identifies calorie restriction as a stressor. This can lead to a spike in cortisol and impair the release of follicle-stimulating and luteinizing hormones. You’re especially susceptible to this the week before your period, when cortisol levels are already naturally higher. 

But it’s not all bad news when it comes to fasting. Research suggests that women with PCOS can benefit from intermittent fasting and some of its side effects such as weight loss and lower blood sugar, leading to improved reproductive health. 

Although there are potential positives, It’s important to recognize that intermittent fasting is not a magic cure for your health and wellness. In fact, research has shown that when weight loss is the goal, a balanced, reduced-calorie diet is equally as effective as fasting. If you still want to try intermittent fasting but want to avoid some of the negative effects on your menstrual cycle, limiting fasting periods to no more than 16 hours per day and avoiding fasting daily for long stretches is a gentler, yet still effective approach.


Written by Laura Jeha

Laura Jeha is Registered Dietician based in Toronto who focuses on plant-centric foods to help people become healthy and happy.