If you’ve nosed around in the posts on my own experiments or read some of my many posts on nutrition and insulin resistance, you might have come across a reference to continuous glucose monitoring. This tool has been a game-changer for refining how I use nutrition to manage my hormonal imbalances. You can read about some of these experiences here.

If you’ve been diagnosed with PCOS, you’ve likely (and hopefully!) had a metabolic blood work panel done that included fasting blood sugar levels and fasting insulin levels. These provide a basic snapshot of your metabolic health at one point in time. If you’re like me, and a relatively small percentage of women with PCOS, your numbers might have been fine, and you might think this post isn’t for you. But I have a working hypothesis that all women with PCOS are insulin resistant during at least some portion of their menstrual cycles, so I'd suggest reading on regardless of what your bloodwork says! 

A Lesson on Carbohydrate Digestion

To understand how continuous glucose monitors (CGMs) work, we need to understand a little bit about carbohydrate digestion.

The simplest forms of carbohydrates are glucose, fructose, and galactose. All carbohydrates must be broken down into these simplest forms in the digestive tract to be absorbed. Common table sugar is a compound with only one fructose molecule and one glucose molecule. It is quickly broken down into fructose and glucose to be absorbed by the body. When we consume large amounts of sugar (or other sweeteners like honey, coconut sugar, maple syrup, high fructose corn syrup, etc.), our body quickly absorbs the sugars, raising our blood glucose levels sharply.

More complex carbohydrates contain long chains of carbon, hydrogen, and oxygen atoms, requiring more time to be broken down fully into the simplest sugars for absorption. This leads to a slower increase in blood sugar spread out over a longer duration of time, and hence, the idea that complex carbohydrates provide sustained energy.

Our bodies tightly regulate the concentrations of various substances in our blood, including blood glucose. Glucose is the easiest source of fuel for our cells to use, so we ideally have a stable concentration of glucose at the ready for all of our bodily energy needs. Our body can even convert protein and some fats to glucose to use as fuel when needed. When our blood glucose dips too low, we experience extreme fatigue because our cells don’t have the energy they need to carry out the millions of reactions and processes going on in our bodies at any given time.

But high blood sugar levels are also a problem. 

As blood glucose levels rise past what your body needs at that moment, your pancreas secretes insulin, which is used to signal cells, both muscle and fat cells, to let glucose enter. In muscle cells, glucose is stored as glycogen, prime fuel for your future squats, running, or basic body movements like lifting a fork or typing on your computer. Once your muscle cells are at capacity, the remaining glucose is stored as fat in fat cells for longer-term storage.

When you have repeatedly elevated blood sugar from consuming fast-absorbing carbohydrates regularly, insulin is constantly being secreted. We all know someone who talks too much or maybe nags too much, who we eventually just tune out over time. Well, our cells in the face of ever-present high insulin levels are much the same way; they stop responding to insulin and stop letting glucose in.

Your body’s only mechanism for controlling blood glucose is to secrete insulin, and so in response to your cells tuning out insulin, your body pumps out even more insulin in its struggling attempt to lower blood glucose levels. This vicious cycle is what leads to insulin resistance and eventually type II diabetes and chronically elevated blood sugar levels.

Blood Sugar Regulation and PCOS

A study of the rate of insulin resistance among women with PCOS found that 75% had insulin resistance (Tosi et al. 2017). Given my own experiences, I also suspect that that number is too low. My insulin sensitivity is excellent during the majority of my cycle, so I would have fallen into the 25%, but for about a week during each cycle, my insulin sensitivity is a disaster. But for the sake of argument, let's say at a minimum, the majority of women with PCOS experience insulin resistance.

There is a debate in the literature about whether the excessive androgens, like testosterone, that are present in women with PCOS result in insulin resistance because excess androgens can contribute to insulin resistance. Or whether insulin resistance causes the excess androgens. High insulin can cause the secretion of androgens. It is a true chicken and egg debate, with substantial consequences for women with PCOS.

However, there is some evidence that at least for some women with PCOS, abnormalities in insulin signaling and/or insulin receptors exist (Moghetti and Tosi 2021), and studies have shown that women with PCOS have a harder time clearing insulin from our systems than women without PCOS (Peppard et al. 2001). Other studies have demonstrated that treatment of insulin resistance with Metformin improves fertility outcomes (Morley et al. 2017). These findings suggest that insulin resistance drives excess androgens and impaired reproductive function, for at least some portion of women with PCOS. And in my experience, managing blood sugar and insulin resistance can significantly reduce the most common symptoms of PCOS like acne, excess hair growth on the face and body, hair thinning, and weight gain. 

Reducing insulin resistance also lowers your risk for cardiovascular disease, non-alcoholic fatty liver disease, and obesity.

What Is a Continuous Glucose Monitor (CGM)?

A continuous glucose monitor is a small device that you wear either on the back of your arm or your lower belly. Using the provided sensor applicator, a small wire on the sensor gets inserted into your skill. The wire measures your blood sugar in real time. Then the transmitter on the device sends your data to the paired app on your smartphone. You can watch your blood sugar rise or fall in response to food, exercise, etc.  

When placed correctly, you won't feel the wire sensor in your skin. Fortunately, CGM technology is continuously improving. Newer models are smaller and less noticeable than older models, making them a bit less conspicuous if you're wearing them on your arm. 

Five Ways that a Continuous Glucose Monitor Helps Women with PCOS

If you have any degree of insulin resistance, continuing to consume foods that cause large blood sugar spikes will continue to force your body to pump out high levels of insulin. This cycle will only increase your degree of insulin resistance over time and lead to chronically elevated androgen levels (levels of male hormones).

1. Continuous Glucose monitors who you in real-time how your body responds to certain foods.

While we have tools like the glycemic index (see my post on this), this index is based on the average person. Across people with the same insulin sensitivity, individual responses to certain foods will vary for a variety of reasons, including differences in your microbiome, differences in how quickly you digest certain foods, differences in stress levels, etc. 

The glycemic index, and corresponding glycemic load, are great places to start, but if you’re finding yourself still struggling with signs of insulin resistance and PCOS symptoms, a CGM might be useful to see if there are foods you’re eating regularly that just aren’t working for you. I have a client for whom tomatoes cause giant blood sugar spikes. This was quite unexpected given that tomatoes have both a low glycemic index and low glycemic load. I’ve also seen clients who are quite sensitive to fruit sugar. Learning these things allowed them to adjust their diet and improve their symptoms.

2. Continuous Glucose Monitors Help you identify variations in insulin sensitivity across time

There are two main time frames for this.

First, for some females, insulin resistance can vary across their menstrual cycles (Yeung et al. 2010, Brown et al. 2015). When this is the case, some degree of insulin resistance occurs during the luteal phase of the menstrual cycle (the phase in between ovulation and menstruation, read more about phases here). Not all females experience this, and for those who do, the pattern can vary. For example, I have insulin resistance starting about 10 days before my period, and it pretty much holds steady until my period arrives. One of my clients experiences insulin resistance during the luteal phase of her cycle only during some cycles, and hers follows the more textbook pattern, where insulin resistance peaks mid-luteal phase and gradually improves as her period approaches. For a full discussion of possible patterns, see my post on the topic.

Without a continuous glucose monitor, I would not have known that I had this intermittent insulin resistance. During this phase of insulin resistance, my body’s response to carbohydrates is substantially different than it is during the rest of my cycle, so I adjust my diet accordingly during this cycle phase, consuming almost exclusively low glycemic index and low glycemic load foods (Download my guide to carbs if you haven’t done so yet for a cheat sheet on these foods!) because these are the only carbs my body can handle in this phase without massive blood sugar spikes. This adjustment has helped tremendously with my last lingering PCOS symptoms and has put my cycle firmly in the “normal length” category. Given that I've had irregular periods for about 20 years before adjusting my nutrition, having consistently regular periods is pretty exciting to me!

During the rest of my cycle, I go back to regularly consuming carbs in the lower three levels of my PCOS carb pyramid, and every so often in the upper two levels of the pyramid.

The second time domain for which insulin resistance can vary is within a single day. This pattern can also vary across people, but I have most commonly observed a decrease in insulin sensitivity in the evening in both myself and some of my clients. This is usually caused by the secretion of melatonin in the evening, which for some people can reduce insulin sensitivity (Garaulet et al. 2020). Now that I know I’m less insulin sensitive in the evening, I keep my evening carbs in the low glycemic index and low glycemic load category on most days, enjoying carbs with higher glycemic index or load earlier in the day. I do, however, still enjoy going out for sushi or a nice steak with a side of mashed potatoes every so often. What matters most is what we do most often; we don’t need to be perfect!

3. Continuous glucose monitors can show you how lifestyle factors and risk factors affect your blood sugar levels.

The most common factors include:

1. Poor sleep - Your CGM will likely show that your blood sugar levels are higher and spike more easily after a night where you slept poorly or not enough. Inadequate sleep is associated with higher fasting blood glucose levels and increased risk of metabolic syndrome (Che et al. 2021). 

2. Stress - Many of us struggle with chronic stress. Our body's stress response evolved in a time of major physical stressors where we had to be prepared to fight or flee from wild animals. In our current lives, our stressors are rarely physical, but the stress response has not adapted to this change. Consequently, when we're stressed, our bodies still prepare us to fight or flee by increasing blood sugar levels that they think will be necessary for the impending physical activity. But... we don't need to fight or flee and so our blood sugar just remains elevated for no reason.

3. Illness - If you're sick while wearing a CGM sensor, you'll likely see elevated blood sugar levels and bigger blood sugar spikes. Colds and other illnesses have a similar effect on the body as stress. 

4. Continuous glucose monitors can show you how positive lifestyle factors can improve insulin sensitivity.

These things include:

1. Exercise - The effect of exercise on insulin sensitivity varies a bit across people, but most people will experience increased insulin sensitivity after working out. This means that we can consume a higher carbohydrate meal in this window without creating a large blood sugar spike. Regular exercise, including both moderate-intensity exercise and high-intensity interval training, can also improve insulin sensitivity in the long run.

2. Strength training - Strength training will have benefits over the long term, so you might need to use your CGM device for a while before seeing the full effects, but strength training increases your muscle mass and your muscle mass is a healthy place for your body to store glucose. Muscle mass is also more metabolically active than fat. Having more muscle increases the amount of calories your body burns, even at rest. Studies show the increased muscle mass, relative to your body weight decreases insulin resistance and risk of metabolic syndrome (Srikanthan and Karlamangla 2011).

3. Getting adequate sleep and managing stress - See above as to why!

5. Continuous glucose monitors can tell you how well a certain blood sugar hack works for you. 

There are a variety of tools and lifestyle changes that can help improve insulin sensitivity and/or prevent large blood sugar spikes from occurring after consuming a given meal. You can find a full discussion of these tools in this post. A continuous glucose monitor lets you see exactly how any given tool works for YOUR body! Just like bodies differ in how they respond to individual foods, they also vary in how they respond to individual tools. A continuous glucose monitor can help you determine the most effective tools for you.

There are a variety of tools that can help improve insulin sensitivity and/or prevent large blood sugar spikes from occurring after consuming a given meal. You can find a full discussion of those tools in this post. A continuous glucose monitor lets you see exactly how any given tool works for YOUR body! Just like bodies differ in how they respond to individual foods, they also vary in how they respond to individual tools. A continuous glucose monitor can help you determine the most effective tools for you.

Getting Started with a Continuous Glucose Monitor

If you’ve made it this far, you are probably at least considering using a continuous glucose monitor. There are a lot of options out there as well! My personal favorite is the continuous glucose monitor and corresponding app provided by Signos. It’s easy to set up, easy to log your food, exercise, sleep, and more, and it provides reports for you on how your body responds to different foods. If you pre-log a food that you’ve eaten before, it will even give you a nudge if it’s not your best choice. 

I generally recommend purchasing at least 3 months' worth of CGM sensors. In the first month, I'd suggest trying to stick to your normal diet as much as possible and experiment with eating all of your favorite foods to learn how each one affects your blood sugar. You can also experiment with the various tools that can help to reduce blood sugar spikes.

Then in the next two months, you can start to adjust your diet based on what you learned about your glucose response to different foods in the first month. Eliminating the foods that cause your biggest spikes can have a substantial effect on your blood sugar and PCOS symptoms. And we don't need perfection. I shoot for about 80 - 90% "compliance" with my PCOS plan. 

If you want some personalized assistance using your continuous glucose monitor, you can also explore options for working with me. I’m a huge fan of CGMs, and I’d love to work on them with you! Send me an email (kelly@theprosprofessor.com) if you have questions or leave a comment below.

References

Brown SA, Jiang B, McElwee-Malloy M, Wakerman C, and Breton MD. 2015. Fluctuations of Hyperglycemia and Insulin Sensitivity Are Linked to Menstrual Cycle Phases in Women with T1D. Journal of Diabetes, Science and Technology 9(6):1192-1199.

Che T, Yan C, Tian D, Zhang X, Liu X and Wu Z. 2021. The Association Between Sleep and Metabolic Syndrome: A Systematic Review and Meta-Analysis. Frontiers in Endocrinology, 12:773646. doi: 10.3389/fendo.2021.773646

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

Moghetti, P. and F. Tosi. 2021. Insulin Resistance and PCOS: Chicken or Egg? Journal of Endocrinological Investigation 44:233-244.

Morley LC, Tang T, Yasmin E, Norman RJ, Balen AH (2017) Insulin-sensitising drugs (metformin, rosiglitazone, pioglita- zone, d-chiro-inositol) for women with polycystic ovary syn- drome, oligo amenorrhoea and subfertility. Cochrane Database Syst Rev 11:CD003053 

Peppard HR, Marfori J, Iuorno MJ, Nestler JE. 2001. Prevalence of polycystic ovary syndrome among premenopausal women with type 2 diabetes. Diabetes Care 24:1050–1052. 

Srikanthan P and Karlamangla AS. 2011. Relative Muscle Mass Is Inversely Associated with Insulin Resistance and Prediabetes. Findings from The Third National Health and Nutrition Examination Survey. The Journal of Clinical Endocrinology & Metabolism, 96(9):2898–2903, https://doi.org/10.1210/jc.2011-0435

Tosi F, Bonora E, Moghetti P. 2017. Insulin resistance in a large cohort of women with polycystic ovary syndrome: a comparison between euglycaemic-hyperinsulinaemic clamp and surrogate indexes. Hum Reprod 32:2515–2521. 

Yeung EH, Zhang C, Mumform SL, Ye A, Trevisan M, Chen L, Browne RW, Wactawski-Wende J, and Schistermen EF. 2010. Longitudinal Study of Insulin Resistance and Sex Hormones over the Menstrual Cycle. The BioCycle Study. The Journal of Clinical Endocrinology & Metabolism 95(12):5435-5442.

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.