Last week, I listened to Dr. Aviva Romm’s On Health podcast episode on intermittent fasting and time-restricted eating, which she refers to as time-based eating. On the podcast, she talks about how helpful she has found time-based eating to be for her female clients. Many years ago, I tried time-based eating as part of a “body composition challenge” being offered at my CrossFit gym, and I found it to be pretty horrible for me! If I recall correctly, I think I started with 12 hours of fasting with a 12-hour feeding window (this is a VERY liberal feeding window for this kind of fasting) or perhaps it was 14 fasting, 10 eating. I’m not sure! In either case, it was not as long of a fasting period as is generally recommended, and it was pure torture for me. As I anxiously waited for the start of my feeding window, I was full-on “hangry” and couldn’t focus on anything.

When my feeding window started, I stuffed my face with food. For the entire rest of the day, all I could think about was eating. I’m certain I ate more than I normally would have, just in a shorter period of time. I tried again a few days later, and the same thing happened. When I reached out to my coach, he basically said, “Suck it up and deal with it.”

So I started looking up if perhaps there was something about my body that didn’t agree with time-based eating. I learned that there wasn’t much research done on any forms of fasting among pre-menopausal women and that our bodies might be more sensitive to threats of famine than male bodies or post-menopausal women. This made sense to me and seemed to fit with the severe anxiety that was triggered in me when I couldn’t eat food when I wanted it.

So I stopped fasting and went on with my life.

But… I really respect Dr. Romm, and after listening to her podcast, I decided to re-investigate how time-restricted eating or fasting might help me or my clients. I figured more research had been done that could shed more light on the topic for women, and indeed, that is the case. I will admit that my stance has softened on the strategy, though I think there is still a lot of research left to be done.

Terminology

Before we dig into what I found, I want to clarify some terms, as Dr. Romm also did on her podcast.

We often use the term “intermittent fasting” to refer to a shortened feeding window on any given day. This form of fasting is actually time-restricted eating. Intermittent fasting refers to the practice of going at least 24 hours without food. I cannot find any research on the use of this more extreme tool for PCOS, so I won’t be discussing it here. Instead, I’ll focus on time-restricted eating.

Time-Restricted Eating and PCOS: What does the research say?

Two studies consider the use of time-restricted eating among women with PCOS. The first one, a study of women with PCOS fasting for Ramadan (Zangeneh et al. 2014) is honestly subpar in quality, and I wouldn’t personally use its findings to make recommendations, but it is often cited as proof of the use of fasting (or time-restricted eating) for women with PCOS, so I want to take a minute or two to talk about it.

Fasting during ramadan

This study recruited 40 female patients from the Infertility Center of Royan Institute in Iran, all of whom had been diagnosed with PCOS. Twenty of these women were fasting for Ramadan, while the other 20 were not fasting. The paper does not say that the fasting treatment was randomized across the women; it sounds like the fasters had chosen to fast, while the others either did not follow the practice or had another reason to abstain from fasting, such as an illness.

The researchers did not collect baseline data from the participants, so it is unclear if the various hormonal measures considered differed between the two groups of women before fasting even started. This lack of baseline data is even more concerning given the fact that the treatment wasn’t randomly assigned to the women.

The researchers also do not say when during Ramadan the measurements were taken, only that they were taken while the Ramadan observers were fasting.

All participants were between 20 and 40 years old, with an average age of around 29. The researchers found no differences between the two groups in terms of follicle-stimulating hormone, luteinizing hormone, testosterone, adrenaline, beta-endorphin, or fasting insulin. They do find that the fasting group had lower cortisol and lower nor-adrenaline, two stress hormones, than the non-fasting group. However, we do not know if this group had lower levels of these two hormones before the fasting period began. Stressful life circumstances might be the reason why the non-fasting group was not fasting. If this were the case, then fasting could have had no impact on stress hormones. We can’t be sure without additional information.

Given all of these drawbacks, I would use caution when citing this study as a reason to use fasting among women with PCOS.

time-restricted eating May significantly improve hormone levels in overweight women with pcos

A second study utilizes far superior research methods (thank goodness!), and hopefully, more such studies will follow to make sure the results are reproducible. This study (Li et al. 2021) recruited 18 women with PCOS between the ages of 18 and 31 who were anovulatory (did not have naturally occurring periods) and had BMIs of at least 24. A BMI of 25 or more is considered overweight, so it is unclear why they chose 24 as their lower bound. However, their average BMI was 29.75, just below the cutoff for obesity, so we can generally categorize their study population as meeting the BMI criteria for being overweight. All participants were outpatients at the Department of Endocrinology at the Shengjing Hospital of China Medical University. The study excluded women who were taking hormonal birth control, insulin-sensitizing medications, statins, or fish oil, and those with a history of fasting or a history of engaging in high-intensity exercise. The recruited women were also healthy except for their PCOS diagnosis.

This study did not have a control group, which they would ideally have included in case there were outside trends that would have led to changes in the parameters being measured. For example, let’s say we’re running a study on a new diet, and we start the intervention right after the start of the new year. We then re-measure our participants post-intervention a month later. We’d expect weight to a decline a bit on average, even in the absence of the diet intervention because most of us eat a bit more at holiday gatherings and then return (hopefully!) to our baseline weight sometime after the holidays are behind us. In this example, we would use a control group to net out the trend happening in the general population from the impact of the diet intervention being studied. This helps to remove spurious correlations. Previous studies looking at other kinds of PCOS interventions generally only find declines in wellness parameters among the women in their control groups across time. Given this, we can reasonably assume that any positive changes could be attributed to the time-restricted eating intervention, but a better research design would be more compelling.

Okay, back to the study…

During the first week of the study, participants ate as they normally did and kept track of their food consumption. They also weighed themselves each day, and the researchers took a variety of baseline measurements (unlike the Ramadan fasting study), which will be discussed further below.

During the next 5 weeks of the study, all of the participants were asked to fast for 16 hours and eat within an 8-hour window, from 8 am to 4 pm each day. They were asked not to adjust their diet in any way (in terms of total calories or macronutrient composition) relative to their baseline diets.

Three of the participants dropped out after just the first baseline week (pre-time-restricted eating), but all of the 15 who started the fasting protocol completed it.

Despite not reducing caloric intake, participants lost an average of almost 3lbs, saw a one percentage point reduction in their body fat percentage, and experienced a 6% reduction in visceral fat area.

In terms of insulin sensitivity, participants experienced a 21% reduction in fasting insulin, a 28% improvement in their handling of an oral glucose drink, and a 21% reduction in HOMA-IR (a measure of insulin resistance). All of these changes are substantial improvements.

Participants experienced no changes in triglycerides, total cholesterol, or LDL cholesterol.

In terms of reproductive hormones, participants experienced an average of a 9% reduction in total testosterone, a 19% increase in sex-hormone binding globulin (which we want to see increase to reduce free testosterone), and a 26% decrease in free androgen index. These changes would all help to address PCOS symptoms like acne and hirsutism.

The team did not find changes in luteinizing hormone (LH), follicle stimulating hormone (FSH), or the ratio of LH to FSH (this ratio tends to be high in women with PCOS, impeding ovulation). Despite a lack of change in LH/FSH ratio, 11 of 15 participants saw improvements in menstrual irregularity, although it is not clear from the paper how this was measured.

Lastly, the participants saw substantial reductions in C-reactive protein, a measure of general inflammation, and insulin-like growth factor 1.

Given the far-reaching impacts found among participants, I am less concerned about the study’s lack of a control group. This seems like compelling evidence to me that time-restricted eating could be a useful tool for many women with PCOS.

Why does time-restricted eating help with pcos?

Time-restricted eating often, although not always, has been shown to improve insulin sensitivity. With insulin resistance being a primary underlying factor for the reproductive hormone effects found in PCOS, it makes intuitive sense that improving insulin sensitivity would also improve reproductive hormone levels.

The weight loss findings here are perhaps less intuitive at first glance. The participants did not change their caloric intake or food composition, but still lost weight and body fat. This is likely coming through changes in the amount of time per day that insulin was present in participants’ bodies as they changed their eating timing.

Whenever insulin is present, it inhibits fat from being broken down. In a well-functioning body, the presence of insulin correctly tells the body that there is plenty of (or maybe too much!) glucose available in the blood to use for energy, so tapping into fat stores is not needed. If you have insulin resistance, your body produces more insulin that it otherwise would in response to a given amount of carbohydrate consumption, and your blood sugar remains high for longer. This extended presence of insulin prevents fat loss, even if you’re eating in a caloric deficit.

Studies have shown that women with PCOS take longer to clear insulin from their bodies. When you have insulin resistance AND your body takes a long time to clear any insulin, you likely have chronically elevated insulin levels all day long if you are eating all day long. Under these circumstances, fat loss will be very difficult, no matter how much you restrict caloric consumption.

With time-restricted eating, you have a larger window of time without food being digested, which means you have a longer window of time for insulin to be cleared from your system and for your body to switch to fat-burning mode. Thus, we can maintain eating the same amount of food per day, just within a smaller time window, and potentially lose weight, and importantly, also lose fat.

Note, however, that there are also plenty of other ways to address insulin resistance, which will help with weight loss. You can find an overview of several options here, a discussion of the impact of exercise on insulin resistance here, and two posts on meditation and their impacts on insulin resistance here and here.

Time-restricted eating is not the only way! But it is one way!

timing window, participant criteria, and future research

I think it is important to note that the eating window in this study started relatively early in the day. Many studies of time-restricted eating entail skipping breakfast and starting the feeding window around noon. Given the data from my own continuous glucose monitor, as well as data from my clients’ CGMS, I think the earlier window considered in this study is helpful from a blood sugar regulation perspective. Melatonin can interfere with insulin sensitivity, with the degree of interference in part determined by genetics (Garaulet et al. 2020). When I’ve consumed carbohydrates closer to bedtime, I’ve observed my blood sugar spiking higher overnight than the same food would have done if consumed earlier in the day. And when these spikes have occurred, my blood sugar has remained dysregulated, with peaks and dips occurring for hours. An earlier eating window would avoid this issue.

I would LOVE to see a study that compares the earlier window tried here with a more traditional window of perhaps 11 am - 7 pm or 12 pm - 8 pm, done with women with PCOS (of course!).

I’d also like to reiterate that the study excluded women with a BMI less than 24 and women who engaged in high-intensity exercise. While I’m still working my way through the time-based eating criteria, I have yet to find a study that considers lean women with or without PCOS who engage in high-intensity exercise (i.e., women like me). If you know of such a study, please send it my way!

Lastly, the research I have seen so far has not seriously considered the impacts of longer-term time-restricted eating on menstrual cycle regularity. The study above said it improved but did not provide a metric for this improvement. Given that the intervention only lasted 35 days, and the study group was anovulatory to start, this seems like a narrow window to determine cycle regularity, unless they were tracking ovulation. It doesn’t appear that they did this. In other studies that compare pre- and post-menopausal women, they compare markers like insulin resistance and weight loss and generally find no differences between the two groups, but they don’t measure (or don’t report) metrics of menstrual cycle regularity. This seems like a key parameter to me!

take home points

Just 5 weeks of time-based eating led to significant improvements in insulin sensitivity, reductions in body weight and body fat percentage, and improvements in the hormonal profiles of women with PCOS.

Participants ate between 8 am and 4 pm and did not restrict total calories consumed per day.

Future research is needed to determine the optimal feeding window, more research is needed on a wider range of female participants, and research needs to be better at considering the impacts of time-restricted eating on menstrual regularity.

References

Garaulet M, Qian J, Florez JC, Arendt J, Saxena R, Scheer FAJL. 2020. Melatonin effects on glucose metabolism: Time to unlock the controversy. Trends Endocrinol Metab, 31(3): 192–204. doi: https://doi.org/10.1016/j.tem.2019.11.011

Li C, Xing C, Zhang J, Zhao H, Shi W, and He B. 2021. Eight-hour time-restricted feeding improves endocrine and metabolic profiles in women with anovulatory polycystic ovary syndrome. J Transl Med, 19:148. https://doi.org/10.1186/s12967-021-02817-2

Zangeneh F, Abedinia N, Naghizadeh MM, Yazdi RS, and Madani T. 2014. The effect of Ramadan fasting on hypothalamic pituitary ovarian (HPO) axis in women with polycystic ovary syndrome. Women’s Health Bulletin, 1(1):e18962. DOI: https://dio.org/10.17795/whb-18962

Disclaimer: This post is not intended to diagnose or treat any medical issues. It is intended for informational purposes only. I am not a medical practitioner. Always consult a trusted healthcare provider with any questions you may have about a medical condition or treatment and before starting any new health care regimen.