Join the Conquer PCOS Course today!

Hi, I’m Alyssa! AKA, The PCOS Nutritionist Alyssa!

I’m a Registered Dietitian dedicated to helping you eliminate your PCOS symptoms with sustainable and realistic nutrition changes.

Some of Our Favorite Products

Intermittent Fasting for PCOS: A Dietitian Weighs In

Have you considered trying intermittent fasting for PCOS? 

Intermittent fasting has become increasingly popular in recent years. People claim it has several benefits from weight loss and improving heart health to anti-aging properties. 

Women with polycystic ovary syndrome (PCOS) are also showing interest in this diet trend. But is intermittent fasting a good idea for the management of PCOS symptoms? 

As a registered dietitian who also lives with PCOS, I understand firsthand how difficult it can be to navigate this hormonal disorder. My goal is to make eating well for PCOS realistic and straightforward. 

Before we dive into intermittent fasting for PCOS, let’s do a quick recap of what PCOS is.

Clock laying on an empty plate alongside a fork and knife. A fabric tape measure is draped over the corner of the plate also.

What Is PCOS?

Polycystic ovarian syndrome (PCOS) is a common endocrine disorder that affects up to 20% of women of reproductive age worldwide (1). Some of the most common PCOS symptoms include menstrual cycle irregularities, infertility, and weight gain, however it can present in various ways.

Symptoms of PCOS may include:

  • Hirsutism (unwanted hair growth, particularly body and facial hair)
  • Hair loss
  • Acne
  • Irregular periods
  • Weight gain
  • Infertility
  • Mood swings
  • Painful periods

Although PCOS was previously thought to only affect young women of childbearing age, we now know that this is a lifelong condition. Unfortunately, those with PCOS are at an increased risk of developing type 2 diabetes mellitus, high blood pressure, metabolic syndrome, heart disease, and even endometrial cancer. 

The good news though is that a healthy diet and lifestyle changes can help to reduce your symptoms and also reduce your risk factors for developing other health problems. 

PCOS: Why What You Eat Matters

Although the exact cause of PCOS remains unknown, researchers believe that several driving factors are at the core of PCOS, including insulin resistance, chronic inflammation, and/or adrenal dysfunction.

Insulin resistance is very common in those with PCOS. In fact, up to 80% of those with PCOS are insulin resistant, or have impaired glucose metabolism (2). 

With insulin resistance, your body’s cells aren’t as sensitive to the hormone insulin, which is responsible for regulating your blood sugar levels. This can lead to high insulin levels, leading to a myriad of issues from high testosterone levels to fatigue to weight management struggles. 

The foods you eat can directly influence insulin resistance and inflammation. 

Including nutrient-dense foods such as fruits, vegetables, whole grains, legumes, lean proteins, and healthy fats can help reduce insulin levels and inflammation. On the other hand, a diet high in refined grains, sugar, processed foods, and alcohol may worsen insulin resistance and inflammation. 

To learn more about which foods can help to reduce inflammation, check out this list: Anti-Inflammatory Foods List PDF: Dietitian Approved

Now that we know a little more on how food can impact our PCOS, what is the best diet to follow? Let’s explore intermittent fasting for PCOS

What Is Intermittent Fasting?

Unlike diets that tell you what to eat, intermittent fasting focuses on when to eat.

Intermittent fasting is any eating plan that switches between periods of fasting and periods of eating. There are a variety of ways that people can choose to fast and which intermittent fasting plan someone chooses will usually be a personal choice. 

Types of Intermittent Fasting:

  • Time-Restricted Eating: Also called Time-Restricted Feeding, this is perhaps the most popular approach to intermittent fasting. This approach limits your eating to a certain window of time per day. Some common schedules are 16:8 or 20:4. In a 16:8 fasting schedule, you would abstain from food or calorie-containing beverages for 16 hours in the day and then eat all of your calories during an 8-hour window of time. 

  • 5:2 Diet: This approach entails eating normally for 5 days of the week. On the remaining 2 days, you limit yourself to 500-600 calories per day. 

  • Alternate-Day Fasting: This approach alternates between your regular eating pattern one day and a fasting period the next day. You then resume your regular eating pattern for one day and follow with another fasting day, and so on. There are different variations to what constitutes a fasting day. Some variations will limit to 500 calories that day (or ~25% of estimated calories), while other variations will limit to zero calories on a fasting day.

So now that you know what intermittent fasting is, you’re probably still wondering if it’s a good idea for PCOS.

PCOS And Intermittent Fasting

Research for PCOS is lacking across the board. So it should come as no surprise that the research on intermittent fasting and PCOS is also lacking. 

Most people with PCOS are interested in intermittent fasting because of the belief that it improves insulin sensitivity and can help with weight loss

There are some benefits of intermittent fasting seen in the few studies we have, however, there are some serious drawbacks also. Let’s take a look.

Benefits Of Intermittent Fasting

A recent study examined the effects of time restricted eating on PCOS; particularly an 8-hour eating window.

Those in the study were instructed to consume all of their calorie intake from 1pm to 9pm for a total of 6 weeks. They were not instructed on any sort of calorie restriction; the only instruction they received on their food intake was to limit simple carbohydrates as much as possible. 

After the 6 week period, time restricted feeding led to a decrease in body mass index (BMI), fasting insulin, fasting glucose, hemoglobin A1c, LDL (bad) cholesterol, and triglycerides. HDL (good) cholesterol had increased. 

In terms of reproductive hormone levels, AMH, LH, DHEA-S, free androgen index (FAI), and testosterone levels were significantly lower. On the other hand, TSH (thyroid stimulating hormone) increased, which may be harmful for some women. 

It’s important to note that this study only had 30 participants who completed the 6 week trial. Those 30 women were between 21-33 years old and had a BMI between 18 and 30. Anyone with a BMI under 18 or over 30 were excluded from the study, as was anyone taking hormonal birth control.

Another study had similar results as the previously mentioned study. This study had an even smaller sample size of 18 women with PCOS. Only 15 women completed the 6 week long trial that consisted of eating all of their daily calories within an 8 hour window. 

Overall, research on intermittent fasting and PCOS has been positive. It shows that time restricted feeding improves endocrine parameters, cholesterol levels, hormonal imbalances, and aid in maintaining a healthy weight. 

Now let’s talk about the downsides or potential negative effects of intermittent fasting on PCOS.

The Cons

Although the clinical results outlined above are very promising overall, let’s keep in mind the big picture. These studies were both done with extremely small sample sizes…a total of less than 50 women with PCOS to be exact. 

Six weeks is also a very short period of time to evaluate the effectiveness of any dietary approach. The long-term effects aren’t known – would the positive results continue? Or would there be any adverse effects that occurred after months or years of fasting?

Besides clinical results like lower BMI or lower testosterone levels, there’s also the sustainability factor, which I feel is just as important to address. 28% of the participants reported feeling hungry either daily or several days per week. Who likes to be hungry?! Would those who reported hunger have been able to continue to follow this eating pattern for longer than the trial?  

PCOS is such an interesting condition that can present so differently in women. The exclusion criteria for these studies narrowed down each study to a very small representation of women with PCOS. It’s impossible to say if fasting would yield the same results for everyone with PCOS. 

Intermittent Fasting In Non-PCOS Studies

Since we only have limited research on intermittent fasting for PCOS, we can also look at some of the research done in the non-PCOS population.

Metabolic Health – Insulin Resistance, Cholesterol, & Weight

While a quick search through the research shows some promising results for lower glucose, insulin, cholesterol, weight, it’s important to know that most studies are considered short term studies. 

There are very few studies that look at the effects of more than 6 months of fasting. The studies that are considered longer term have a higher dropout rate and a recent systematic review and meta-analysis showed that fasting didn’t lower body weight, glucose, insulin, or cholesterol levels any more than traditional dieting or healthy eating practices (3, 4). 

It’s also incredibly important to note that most studies on fasting are done in men…and we all know how different women are so we can’t just blindly assume these results will also apply to women (especially women with PCOS). In fact, one study showed that fasting improved glucose in men while negatively impacting glucose in women (5).

Reproductive Hormones

Intermittent fasting may negatively impact reproduction in several ways. If someone is not eating adequate calories, the body can perceive this as a threat and slow or shut down any “extras” like reproduction. Your body doesn’t want you to potentially become pregnant if it suspects you don’t have access to adequate nutrition to support yourself and another human.

Intermittent fasting has shown mixed results as to its effects on estrogen levels, which may negatively affect reproduction in some populations. 

Cortisol Levels

Intermittent fasting usually equates to skipping breakfast for most people. Skipping breakfast is associated with a disruption in cortisol metabolism leading to increased cortisol levels (6). 

Cortisol (aka our stress hormone) can worsen insulin resistance over time. It can also disrupt our circadian rhythm, making sleep more difficult to achieve and further perpetuating the hormonal imbalance. 

Why I Don’t Recommend Intermittent Fasting For PCOS

Ok, I’m going to come right out and say it: I don’t recommend intermittent fasting for PCOS. I mean, this is a page that preaches about sustainable and realistic diet patterns to manage PCOS so this hopefully isn’t a surprise. 

For me, the research just isn’t there. The amount of research done on fasting in those with PCOS is extremely limited by small sample sizes and short-term trials. 

Through research, we know that even in those without PCOS, intermittent fasting doesn’t lead to better results than traditional dieting or healthy eating approaches. 

Research has also shown us that those with PCOS struggle with eating disorders at a significantly higher rate than the general population. Restrictive diets, such as intermittent fasting, can be harmful in creating or exacerbating an eating disorder. 

We also know that restrictive diets don’t work long term for the vast majority of people. So people tend to jump from one diet to the next. This can lead to weight cycling, where your weight goes up and down over and over again. Weight cycling is correlated to gradual weight gain over time and is actually more harmful for hormone health in the long run.

Before considering a restrictive diet, you should always ask yourself: “is this something I can see myself doing for the rest of my life?” If the answer is no, the best thing you can do for yourself is to not start that diet at all. 

Here’s What I Recommend Instead

  • Utilize the time you’re sleeping overnight as your fasting window. This usually means fasting naturally for about 10 hours for most people
  • Eat breakfast daily, ideally within a couple hours of waking up (no, coffee doesn’t count as breakfast either)
  • Eat balanced meals and snacks throughout the day to maintain balanced blood sugar levels

For a more balanced approach that can still manage your PCOS and overall health, check out this post: A Dietitian’s 7-Day PCOS Diet Plan (PDF Included) 

I see women successfully manage their PCOS all the time with a balanced and sustainable diet that allows them to eat when they’re hungry rather than when the clock tells them they can eat. 

The Bottom Line

Researchers have conducted extremely limited research on PCOS and intermittent fasting. The existing research includes very small sample sizes and researchers have conducted it over short time periods. Therefore, it’s unknown if everyone with PCOS would experience positive benefits or if any negative effects would arise in the long-term.

Research done on intermittent fasting in those without PCOS does not show it to be more effective at lowering weight, glucose, insulin, or cholesterol than traditional dieting or healthy eating approaches.

Fasting may alter your cortisol and thyroid hormones. It may also negatively impact reproduction if you’re unable to consume adequate calories. 

As a registered dietitian, I don’t recommend intermittent fasting to manage PCOS.

Disclaimer: this is for informational purposes only and not intended to replace routine medical care or medical advice. Always consult with your healthcare provider for personalized recommendations on dietary changes that will benefit you. 

Leave a Reply

Your email address will not be published. Required fields are marked *