Should Women Intermittent Fast? How Fasting Impacts Female Hormones
Is intermittent fasting (IF) safe for women? In this post, i’m going to lay out what the science points to, my clinical observations and my OWN personal experience, while including action steps at the end for those of you babes interested in time-restricted eating.
My goal is to give you a comprehensive overview, without being a snooze-fest. If you want to see more science, there are plenty of highly-respected people who have already written awesome posts diving into the science more than I have here:
Stefani Ruper & Mark Sisson
Let’s get this party started.
I’m going into this post assuming that you already know what IF is, but if not, let’s recap real quick. Intermittent fasting is a “style” of eating where you go for prolonged periods of not eating, followed by an eating “window”. During this window, you consume your REGULAR amount of food for the day. There are many different ways to fast including skipping meals, prolonged fasts of 24-48 hours, a technique called Eat Stop Eat and more. There is evidence that fasting has benefits like slower aging, decreased autoimmunity, decreased insulin resistance and even destruction of cancer cells.
I’ve found 14, 16 and 18 hour fasts to be to be the most popular amongst women and there are plenty of ladies that scream the benefits of IF from the rooftops. They report things like weight loss, decrease in autoimmune symptoms, better digestive function and more mental clarity.
THE DARK SIDE OF FASTING
What we don’t hear often in literature and blogs posts is the negative side effects some women are experiencing from prolonged intermittent fasts. Women are reported developing symptoms like:
Sleeplessness + Anxiety
Irregular or Missing Periods
Weight gain or weight loss plateaus
Signs of Hormonal Imbalance like acne and hair loss
Binge Eating & Food Obsession
Early Onset Menopause (as early as mid-twenties)
It’s clear that men benefit, but women? It depends.
What about all that evidence that supports fasting? Many of the scientific studies done point to fasting being beneficial for MEN. And because we know how different men and women are on a biochemical and hormonal level, we might have to consider that intermittent fasting affects women way differently than it does men.
Why? It turns out the those key hormones responsible for regulating ovulation and making sure your sex hormones stay juicy and balanced are HIGHLY sensitive to signals of stress and starvation.
Your reproductive hormones and fasting:
So, we have this triple endocrine axis (which stands for different glands working together) called the HPG Axis. This hypothalamic-pituitary-gonadal axis (say that five times fast) works together to create a perfect symphony of hormones from your brain to your ovaries (or testes) to signal the body to create the hormones/functions needed for reproduction.
It goes like this:
Your hypothalamus (in your brain) releases gonadotropin releasing hormone (GnRH)
GnRH then tells the pituitary to release luteinizing hormone (LH) and Follicle Stimulating hormone (FSH)
LH and FSH then act upon the gonads (aka your ovaries) by triggering the production of estrogen and progesterone — the hormones needed to release a mature egg (aka ovulate) and support a pregnancy.
Obviously, if this doesn’t happen on a very regular and specific cycle in women, things can get out of whack real quick. And as it turns out, GnRH pulses are VERY sensitive to environmental factors, including starvation and stress signals that can be caused by fasting.
I don’t know about you, but I would like my hormonal pulses to stay intact, TYVM.
What the studies show:
Sadly, there are no human scientific studies to illustrate. But, there was a fasting study done (you can view it here) on young female rats that is very illuminating.
In the study, they took 10 male and 10 female rates and allowed half to eat whenever they wanted and half to eat every second day. This was done for 12 weeks (an equivalent to 10 years of human life). It only took 10-15 days to have an effect on the females.
Here’s what was observed:
They lost 19% of their bodyweight — you might be like “ohhh awesome”, but note, I did not say “bodyfat” I said WEIGHT. It looks like this wasn’t just loss of fat, but loss of muscle and organ mass as well.
Blood glucose levels were lower
Their ovaries had shrunk — not a promising sign
LH went significantly down — if LH isn’t signaling your ovaries to make estrogen and progesterone, your cycles and fertility will suffer.
Estradiol (a hormone that inhibits GnRH) increased by 4x — high estrogen inhibits GnRH
Leptin – the hormone that tells your brain your fed, safe and okay – was 6x lower
Safe to say, prolonged fasting is probably not a good idea for women of reproductive age until further research is done to make sure it’s 100% safe.
Your hormones are IMPORTANT.
You might be wondering: So, what’s the biggie if I miss my period and am not fertile? I’m not trying to get preggo anyways.
I’m so glad you asked.
Your period is not just for pregnancy. The hormones that regulate fertility are HIGHLY tied to your physical and emotional well-being.
Estrogen impacts fat storage, brain function, moods, digestion and bone formation just to name a few.
Progesterone impacts sleep, moods, fluid retention, brain function, aging, thyroid function and skin health to name a few.
You can bet your own booty that if you aren’t menstruating, you have disrupted hormonal function which will impact how you feel on a day to day basis.
SHOULD YOU FAST AT ALL? HOW I AIM TO GET THE BENEFITS OF FASTING IN MY OWN LIFE.
Now, this is what works for my body, but as you know, I encourage women to tap in, tune in and to above all, LISTEN TO THEIR BODIES. Every body is a so different that sometimes, what works for one, might not work for another.
I personally have found great benefit from eating according to the circadian clock and leaving a 12 hour window between my last meal of the day and my first meal of the next day. I’ve experienced:
Insulin Sensitivity and Blood Glucose Stability
Better Sleep + Waking Up Feeling More Rested
More mental clarity and focus throughout my day
Decreased Autoimmune Symptoms
For example: if I eat dinner around 7pm, I take a mental note of the time. I make sure not to eat until at least 7am the next day. Some days, depending on which part of menstrual cycle I am in and my hunger signals, I will push this a little longer. Seems completely doable and normal right? This is because I am following my body’s natural internal clock and never pushing it beyond what it tells me to do.
NOTE: You might recall that at the beginning of 2018 I was experimenting with daily fasts of 16-20 hours. At first, I felt amazing. Had tons of mental clarity, was losing fat like crazy and lots of energy. Unfortunately, after two months of great results, my routine 16+ hour fasts left me going downhill fast. I started experiencing hair loss, fatigue, irregular cycles, complete loss of hunger and weight GAIN. Not to mention I was irritable AF at all times.
Before fasting, you should ask yourself:
Is my body under extra stress during this season of life? Questions like:
+ Am I eating well/enough?
+ Am I stressed out?
+ Am I sleeping well?
+ Am I exercising/moving my body?
If any of the answers to this question is no, I strongly suggest rethinking your idea to practice intermittent fasting. Why? Because not eating well, external stress, lack of sleep and not exercising are all hormonal and metabolic stressors. Add in prolonged fasting and that is a recipe for hormonal disaster.
2. What part of your menstrual cycle you are in?
Menstrual Phase- Don’t push beyond 12 hours. Why? During prolonged fasting, estrogens raise. Before menstruation, you want your estrogen to naturally drop. High estrogen during this time could lead to heavier bleeding, headaches, PMS and moodiness.
Follicular Phase- Yes. Why? Your estrogen and progesterone levels are naturally rising during this time to prepare an egg to be fertilized (ovulation). Because fasting naturally raises estrogen, it won’t interfere with your natural spike. Fasting will be better tolerated during this time.
Ovulation and Luteal Phase- Not beyond 12 hours. Why? Whether your egg was fertilized or not, your body’s whole goal is to protect a potential fetus if implantation did in fact, take place. If you are not eating enough during this time, you could see your hunger hormones — specifically leptin and grehlin — go crazy. Think insatiable hunger and blood sugar issues.
3. Is this a struggle?
Be honest with yourself. Are you listening to your body? Are you pushing through your body’s intelligent wisdom? Are you experiencing insatiable hunger or hormonal issues? It should never be struggle to get through your day, feel good or ovulate/menstruate.
Because 12-14 hour fasts provide us the many benefits of intermittent fasting, I would encourage women of reproductive age to not go beyond 14 hours unless there’s a good reason. For example: you are severely overweight or are partaking for a medical reason and have discussed it with your doctor.
WHEN YOU SHOULDN’T FAST:
If you are already lean and/or calorie restricted
If you are over consuming caffeine and relying on caffeinated beverages to get you through your fast
Have struggled/are struggling with an eating disorder
“But Jess, I fast all the time and am now not sure if it’s working for me or not?”
Your body speaks to you in signs and symptoms, I urge you to listen up.
WARNING SIGNS THAT IF IS NOT WORKING FOR YOU OR YOU’RE PUSHING IT TOO FAR:
+ Tired, but wired feeling
+ Weight gain, especially around your belly
+ Food Obsession or Binge Eating
+ Loss of Your Period and/or Infertility
+ Muscle Loss
+ Hair Loss
But whyyyyy? I want abs *foot stomp*
Weight loss at the expense of hormones and fertility is a poor reason to fast. Ask yourself, what are your motivations?
Our society paints us a picture that a healthy women makes herself SMALLER. Being lean, slim and “toned” is idealized, but this does not make it right for your unique body. Many times, our bodies paint a completely different picture and scream at us to keep a healthy weight as a matter of SURVIVAL.
As I always say, a healthy body is a perfect vessel for pursuing your purpose. Health should be about feeling GOOD and being able to do life WELL. If prolonged fasting makes you feel vibrant, fertile, energized and unstoppable. Awesome. I’m so glad it works for you. But, if you experience the opposite, there are plenty of other ways to pursue higher quality health.
With anything here, my goal is to educate you, so that you feel empowered to make the best decision for your body based on the facts.