If you’re thinking about trying the keto diet for weight loss, you’ve probably heard about some less-than-pleasant side effects you might experience at the beginning, such as the “keto flu.” But one factor you might not have considered is how the keto diet affects your period. That’s why it’s important to educate yourself about these changes before you start the eating plan. This way, you aren’t in for a shock if you notice anything different during “that time of the month.”
As you may be aware, the keto diet is a low-carb, high-fat diet. Going into ketosis — a state in which your body gets energy from fats instead of carbs — can often cause rapid weight loss. But if you start to lose weight quickly, your loose-fitting pants might not be the only instant change you see. Research has shown that quickly shedding pounds can lead to sharp drops in estrogen. This can potentially cause irregular periods at the beginning of your keto diet, especially if you lose a lot of weight in a very short amount of time.
In some cases, women may even experience amenorrhea — the abnormal absence of a menstrual cycle for three months or more — while following a very low-carb diet like keto, according to registered dietitian Mary Jane Brown, PhD.
“The most common cause of amenorrhea is hypothalamic amenorrhea, caused by too few calories, too few carbs, weight loss, stress, or too much exercise,” Dr. Brown writes for Healthline. “Amenorrhea occurs due to the drop in levels of many different hormones, such as the gonadotropin-releasing hormone (GnRH), which starts the menstrual cycle.”
Irregular or missed periods aren’t the only changes women have experienced while following a keto diet. According to the Keto Summit, other women have reported seeing a lighter or a heavier period while first starting out on the eating plan. Yet others have seen their period appear more frequently than they were happening before. It’s no wonder why there’s a whole reddit thread called "Keto and menstruation," which is entirely devoted to discussing this wide range of experiences that women have had while on the diet.
Here’s the good news: Once your body gets used to being in ketosis, your period will likely return to its regular routine, according to Perfect Keto. If it doesn’t, it’s possible that other stressors in your life may be responsible. Remember: Always talk to your doctor before starting any new diet, especially one as restrictive as keto.