Do You Burn More Calories on Your Period?

As Bruce points out, that time of the month doesn’t always have to affect you negatively.

“Your period is not a time to hide,” says Stacy Sims, Ph.D., senior research fellow at the University of Waikato in New Zealand, and author of ROAR: How to Match Your Food and Fitness to Your Unique Female Physiology. “It’s a time to hit those personal bests.”

You read that correctly. “Your levels of estrogen and progesterone are at their lowest during your period, which means your pain tolerance and time to fatigue increase,” Sims says. “And your body can tap into more carbohydrate stores, helping you recover faster than when your hormones are higher.” She explains that this low-hormone phase—a.k.a. your period—is actually a great time to go hard in your workouts, as long as you’re feeling up to it.

LOL-ing at that thought? Well, research suggests that your period may not hamper your performance as much as you’d think: A BMJ Open Sport & Exercise Medicine study in tennis players shows no association between menses and serve speed and accuracy, and a Journal of Sports Medicine and Physical Fitness study found that soccer players performed similarly at various points in their cycle.

Still, some period benefits are overstated, or flat-out wrong. For one, you don’t burn more calories on your period, contrary to some locker room chatter. If anything, Sims says you burn slightly more calories when your hormones are higher (known as the post-ovulation luteal phase) because your heart rate, respiratory rate, and core temperature increase. “It’s very minimal though,” she says. “Approximately 100 calories per day.” And no, getting your period is not like a natural form of “blood doping.” “It’s not about having more blood in your system,” Sims says. “It’s about having reduced effects of estrogen and progesterone, which inhibit your ability to hit top speed.”

But of course, every woman is different. And if your cramps ever kept you curled up on the couch all afternoon, you know that your period hardly guarantees a PR. What’s most important is listening to your body and doing what’s best for you. Here, we address some common period concerns to help you prep for optimal performance, no matter what your uterus is up to.

Why is my poop different?

The drop in hormones during your period can send you to the bathroom, and not just because you need to change your tampon. “Intestinal movements can be faster or slower, which translates into constipation or loose stools,” says Alyssa Dweck, M.D., a gynecologist practicing in Mount Kisco, NY. She suggests avoiding dietary triggers, such as sweet and salty foods, and keeping up your running routine; just make sure there are some bathroom stops along your route.

This isn’t a question but…OMG CRAMPS.

Like a lot of women, you might have cramps at the start of—or throughout—your period because “your uterus contracts to help expel its lining,” according to the Mayo Clinic.

An easy run could help. “Endorphins are your body’s natural painkillers, so you could feel better if you power through your cramps,” Dweck says. If you can predict when they’re coming (try a period-tracking app like Flo), she says to take Advil or Motrin in advance of your period to get ahead of the problem.

Is it normal to lose your period?

Well, it’s common among athletes, but it’s not good. “Your period is a vital indicator of wellness,” says Kirstin Leitner, M.D., an assistant professor of clinical obstetrics and gynecology at Penn Medicine. So, if it disappears (often caused by excessive exercise or low body weight, known as amenorrhea), make an appointment with your ob-gyn ASAP. (Amenorrheamay affect up to half of female athletes at some point.)

Aside from fertility issues, you can experience a decrease in bone density (caused by low estrogen) if your period goes MIA for too long, which puts you at a higher risk of injury, Leitner says. Indeed, high school athletes with irregular periods were more likely to experience a severe injury than girls with normal periods, per a journal of Athletic Training study.

The other end of the spectrum isn’t so great, either: “If you’re soaking through two tampons or pads an hour, you might be at risk for anemia,” Dweck says. Look out for weakness and shortness of breath, and a see a doc if your heavy periods persist month after month.

What about PMS and performance?

You might notice a dip in your mood and motivation the week before your period, which is totally normal. PMS is, in fact, associated with lack of concentration and low motivation, according to an International Journal of Women’s Health study on high school students.

“This is a good time to focus on steady-state runs and higher rep, lower-weight resistance exercises,” Sims says. “Think of your training schedule as a monthly cycle. Give yourself the flexibility to push hard when you’re feeling good and to back off when you’re not.”