Women and Fasting: Does Fasting Affect Your Cycle?

By Jason Fung, MD

Many young women are afraid to fast because they’re worried fasting will be problematic for their cycles.  Ladies worry that is potential disruption in their cycles it may cause them to become infertile or create great difficulty for them becoming pregnant down the road.  This scares a lot of young women away from fasting.  But the truth is, fasting is more likely to regulate your cycle and reduce the symptoms of premenstrual syndrome (PMS) dramatically!

Like many of the women I’ve worked with, I was scared to fast at first without knowing how it would affect my fertility.  I was 27 years old and a metabolic mess.   I was diagnosed with polycystic ovarian syndrome (PCOS) when I was just 14 years old.  Back then doctors told me not to worry, and that I’d “grow out of it”.  Well, I didn’t “grow out of it”.  Overtime it became worse.  And I was petrified of reducing my chances of getting pregnant even more.

As a scientist, I always rely on good quality data to guide my choices, but there was no solid research on fasting and fertility.  So, I put on my scientist hat and decided to think about things from a more practical, evolutionary perspective.  The first things I thought about was breakfast.  Not in the “break you fast sense” but in the traditional “you must wake up and eat immediately” sense that we’ve adopted in the Western world.

I couldn’t help but laugh to my self at the funny images that were popping up in my head as my mind started to take this evolutionary stroll throughout human history.  Cavewomen didn’t wake up and go to their cave refrigerators and pull out a dozen eggs, nor did they go to their cave cupboards and pull out a box of cereal.  We had to hunt and gather.

And what if the weather sucked?  Ironically, I was thinking about this on a very cold, snowy day in January.  What the heck would we have hunted and gathered on this day in Toronto?  Bark?  There was no viable plant life to consume and almost all animals were in hibernation.  No, we would have had to have fasted until there was food to eat, which could have been months.

At the end of the day I concluded two things.  First, women obviously fasted for centuries and had no issues reproducing or I wouldn’t be here, and neither would you.  Second, what did I have to lose?  If you know my story, you know I was a metabolic mess.

Aside from the PCOS, I had fatty liver disease and type 2 diabetes.  I also had this damn weight gain that kept piling on faster each passing year.  My health was going down the toilet before my eyes despite doing everything my doctors and dietician recommended.   At the rate my health was deteriorating, I would be on disability by the time I was 35 and dead by the time I was 40.  I had nothing to lose.

Within six months of fasting intermittently everything about “that time of the month” completely changed for me, and for the better!  For the first time in my life, I started having regular periods every 28 days like clockworks without having to take birth control or any medications to make that happen.  It was incredible!
In addition to my regular cycle, I stopped suffering from premenstrual syndrome (PMS) too.  That was a bloody miracle if there ever was one.  A few days leading up to my cycle, I would avoid boyfriends, friends and family members during this time because I felt so psychotic and would cry at just about everything.  You would have thought I had been trapped in a room watching The Notebook and listening to Adele on repeat.

The emotional upheaval that comes along with PMS is one thing, but the physical pains are another.  The severe back pain and near debilitating tummy craps are just brutal and totally disrupt our day-to-day lives for an entire week all went away.  I started having pain-free periods that lasted from 2-3 days with a lot less bloat.

My appetite changed for the better too!  I stopped craving all of those sweet and salty foods that I once did.  I started to be able to follow my low carb lifestyle during my period with little effort.  Eventually, even the fasting become effortless!

But none of these changes came over night.  And like most things in life, it got worse before it got better.  At first, I thought “maybe it’s just me” but after coaching thousands of women through this, there are some definite trends that have started to appear when women start fasting.

The Tread – The Frequency of Your Cycle

For the first two months of fasting most women report more than usual delayed menstrual cycles.  This really freaks them out and makes them think that either their pregnant, which isn’t always desired, or they think that fasting is destroying their lady bits and they’re going to die.  I’ve had more patients hyperventilate over this than anything else in the seven years we’re run the IDM program.  And I was one of them.

In my case I knew I wasn’t pregnant unless immaculate conception is truly a thing, but I was worried I had destroyed my lady bits too and destroyed my chances of every becoming a mom.  I spent one day crying like a crazy person after my period was 9 days later than usual.

Luckily, I had the benefit of understanding the science a bit better than most.  There were so many changes going on in my body.  I had virtually erased my fatty liver disease over night, and I was losing so much weight!  My whole body was completely out of homeostasis and it was struggling to find it’s new “normal”.  I was able to carry on with my fasting regimen of 42 hours twice on Mondays and Wednesdays and a 24 hour fast on Fridays each week.

To my surprise, the third period I had after I started my intermittent fasting routine happened exactly 28 days after my second period.  The same thing happened on month four and five and six as well.  Ever since then, my cycle has been on time.
Almost every woman I’ve worked with has experienced the same journey as I did.  Some don’t notice the irregularity as much at the start because their cycles have been so unregular for so long.  Regardless, it’s around months three and four when things start to regulate in terms of timing whether or not you’ve had extremely or just mildly irregular periods in the past.  Even women who haven’t had periods in nearly two years start to experience normal cycles within the first six months of fasting – it’s incredible!

The Trend – The Symptoms of PMS

The good news is that these symptoms don’t get worse before they get better despite all the hormonal changes that are occurring in your body when you first start fasting.  We still have the cramping, bloating, cravings and irritability that we’ve always had to the same degree for the first two months into our fasting journey.
Often, I encourage women to fat fast rather than truly fast during this week of the month.  So much of fasting is mind over matter.  If your body is working against you making it difficult for you to fast, you’re not likely to succeed.  This really screws people up because they think they should be able to fast ALL OF THE TIME – but that isn’t the case!  Most often people give up on fasting entirely because they feel like they’ve “failed” at it when they try to fast at inappropriate times.

Stop the madness immediately!  Don’t fast when your body or life isn’t cooperating.  Do you best to fat fast or stick to a low car, healthy fat approach instead for the first few months.

Things really start to improve around month three.  During this time, you’ll find that most of the physical and emotional side effects of PMS start to diminish greatly.  Women report that their appetite is still strong but the cravings for unhealthy, processed carbs has diminished significantly.  I still encourage fat fasting during this time.

The magic seems to happen at month six!  The side effects of PMS are a distant memory, and you feel in control of your diet.  This is when I suggest women start to actively fast during their period.  What’s even better is that they start to notice weight loss during their periods rather than weight gain!  And to add to all of the goodness, women often report that days one through seven of their cycle are the easiest days for them to fast every month!  We always laugh at how freakin’ crazy this sounds because our periods have always been a junk food eating frenzy and weight gaining nightmare.

My advice for the ladies out there who are nervous to fast?  Start out slowly.  Cut out snacking.  Try to eat your dinner an hour earlier if possible.  And start cutting out the meals one by one as you feel comfortable.

Megan Ramos, IDM Program Director

By The Fasting Method

For many health reasons, losing weight is important. It can improve your blood sugars, blood pressure and metabolic health, lowering your risk of heart disease, stroke and cancer. But it’s not easy. That’s where we can help.

Jason Fung, MD

By Jason Fung, MD

Jason Fung, M.D., is a Toronto-based nephrologist (kidney specialist) and a world leading expert in intermittent fasting and low-carb diets.

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