What I Learned from Wearing a Continuous Glucose Monitoring Device for 3 Months

The use of technology to assist in personal health and wellness decisions has exploded over the last decade. From Fitbit, Apple Watch to Garmin, Whoop and the Oura Ring, all of them collect biometric data and present it back to you in order to provide information on informed changes you can make to improve overall health and longevity. And the number of companies and devices and the kind of information they collect continues to expand rapidly. Personally, I have worn an Oura Ring for the last two years and I find it to be very helpful for guiding me to better sleep, one of the four pillars of longevity.


For three months recently, I wore a continuous glucose monitor. Why?


As I have written about before, nutrition is the one thing which impacts your health more than anything else. We all have to eat and those 2,000-2,500 calories you place in your mouth every day have a dramatic impact on both your long- and short-term health.


The Relation of Insulin Resistance and Glucose to Diabetes

One of the main drivers of chronic disease (and 6 out of 10 Americans have at least one chronic condition) is insulin resistance. Insulin resistance is the decreasing response of cells in your body to uptake glucose and use it for energy. Over time, more and more insulin needs to be excreted by your pancreas, typically in response to eating carbohydrates (which turn into sugar). Insulin also signals your liver to store more energy as fat. So the higher the insulin level the more fat your body stores and consequently you are unable to break down fat to use as energy.


The belief is that over one in two Americans has insulin resistance. This worsens as we age but often begins in our 30-40s, though you may not notice anything is wrong at first.


Insulin can be measured in your blood stream as part of routine testing, though few doctors do it. Ask your doctor to do it with your next routine blood tests. While the standard "normal" range (fasting) is 2-20 mIU/L depending on the lab, the academic literature has shown that levels less than 7 are best for metabolic health. Ideally, we would measure insulin dynamically, as we eat different foods and see the response to stress, exercise, etc. Unfortunately, it is not possible to measure it with any current consumer devices.


We can, however, measure glucose as is done millions of times a day by diabetic patients. Home testing of blood sugars has been around for over 40 years and those of you who are diabetic know the drill. At least once a day, you prick your finger and place a drop of blood on a test strip to measure your glucose level. Ideally, the level should be under 100.


About 10 years ago, continuous glucose monitors (CGMs) entered the marketplace. Typically, these devices were reserved for "brittle diabetics," or patients who had significant difficulty controlling their blood sugar levels in order to provide real time feedback on their current glucose level and how much insulin they may need to give themselves on a daily basis. They were often paired with insulin pumps which deliver a continuous level of insulin to Type 1 diabetics who produce little to no natural insulin.


Benefits of Continuous Glucose Monitoring

The ability to see dynamic changes in your blood sugar is game changing for health and longevity. Why?

  • Most of us walk around with the knowledge that sugar laden foods are bad for us, yet we have no immediate feedback to act on that knowledge. Meaning, if you could see the immediate effect of what you eat, such as a sharp rise in blood sugar to over 200 after eating certain food, most of us might say "hey, I should probably stay away from that."

  • Knowledge is power: most of us have no idea what foods actually trigger high insulin release (as measured by spiking blood sugar), so continuous monitoring can help us understand our personal response to foods.

  • Individuals are individuals. While advice like minimizing or avoiding simple or refined carbohydrates is correct and helpful for the general population, how I respond to a particular food may be very different than how you respond to it.

  • The combinations of other SIMPLE activities can have a dramatic effect on blood sugar control.

There are several companies out there now offering this to the public. The one I used was from Levels, which bills itself as a personal data analytics company that converts your personal data to usable information via their algorithms. There are others reviewed in this article, including Nutrisense and January. Most use a standard CGM device and link the raw data to their proprietary algorithms and app which analyzes the rise and fall of your blood sugar. I’ll describe these devices towards the end.


So, what were my results?


Here is one month's worth of "high glucose events," times when my glucose spiked:

Here is the "Activity Catalog," which describes which meals or activities at what times led to good glucose levels or worse ones:

And here was my average glucose over the course of one of the months:

There are also reports which rank each of my meals according to how much they each led to a spike, both the best:

And the "room for improvement" meals:


What I Observed During the Three Months

Data is data and I must confess this information actually opened my eyes to a few things:

  • First, like the vast majority of people, I am very carbohydrate sensitive. In general, I eat less carbs than the average person and focus more on healthy fats and proteins. I have given up, for the most part, on "sweets," and refined grains like pasta, breads and rice. That said it was profoundly evident that when I added carbs to a meal like a piece of gluten free toast with my morning eggs and bacon/sausage then my blood sugar would rise 50 points from my baseline of under 100. If I did not have the bread, I did not see the spike.

  • There is no such thing (for me) as a good complex carbohydrate. You will hear many people say simple carbs like bread, rice and pasta are bad but complex carbs like steel cut oats are okay. Check out the latest recommendations from HHS and USDA on what we should eat daily. The highest spike I had in my blood sugar was one morning when I decided to cook, from scratch, steel cut oats (not instant) and add a small handful of blueberries on top. No added sweetener. My blood sugar went from under 100 to over 200 within an hour and stayed there for close to 2 hours.

  • Mix healthy fats with every meal. Healthy fats come in many forms such as farm raised eggs, grass fed beef, wild caught fish, avocados, Extra Virgin olive oil, and nuts. I have learned over time that by adding these into most of meals I avoid the blood sugar spike that happens. I am even able to enjoy root vegetables (like sweet potatoes) IF I have them with healthy fats and do not see a significant rise in blood sugar.

  • You can eat a lot of food at once — it just depends on the type of food. Specifically, I remember being out at a business dinner with 20 other people where we had hors d’oeuvres and a 3-course meal including wine with dinner. I was particular about not eating carbs early and stuck with non-root vegetables as my main sides with a protein as main course. I had no dessert. I must have had 1500 calories at that meal alone and only saw a modest rise (less than 50 points) in my blood sugar. While I don’t recommend eating that much at a meal it was a good way to test some theories on blood sugar control.

  • Stress (even good stress) really does cause a rise in your blood sugar. During the trial I had occasional opportunities to speak in front of business audiences. While I wasn’t nervous per se I did note a 20-40 point rises in my baseline blood sugar.

  • Walking after dinner has a dramatic positive impact on blood sugar control. In European cities it is common to stroll around the area after dinner. The simple act of walking for a minimum of 10-15 minutes after dinner has a dramatic "dampening effect" on the rise of blood sugar. It makes sense since some of your largest muscle groups are activated and take up sugar and use it for energy for walking. This has been noted by Levels as part of their feedback to their subscribers.

  • Disrupted sleep messes up your blood sugar. While I am usually a sound sleeper on the rare night where I had wine too close to bed or just had a bad night’s sleep I saw morning blood sugars well above my less than 100 baseline.

So, all good – right?


Well for the most part. A few caveats for this "trial" or n of 1. I like to experiment on myself. I’ve tried various fitness routines like triathlons and like tracking stats with the Oura Ring. You can get too bogged down in the data and it drives behavior a certain way. That is of course the intent and it is by nature artificial. You do need to take pictures and log your food and activities. Some of the activities sync with other devices or apps you may already be using. The food however needs to be put in manually. I didn’t mind it although I’m pretty sure my wife had had enough of it by the end.


Costs of CGM Devices

Then, there is the cost. Bottom line, it ain’t cheap.


There are two major CGM devices that most of these companies use, Freestyle Libre by Abbott and Dexcom. The devices are placed on the back of your upper arm (typically) or abdomen via a spring loaded device. It has an adhesive patch which is activated and firmly attaches to your skin for either 14 (Libre) or 10 (Dexcom) days. Levels gives you a large adhesive patch to place over the device.


The Levels subscription is $399 for the first month and $199 per month after that which includes two Freestyle Libre CGM devices per month. Levels is in "beta" testing and foretells of dropping that price eventually. We will see. Of course, it is not covered by insurance if you are not diabetic. Pricing it out at Costco for the Dexcom is around $300 - 400 per month.


What is it like wearing a CGM device?

You can shower and even swim with the device in place. It senses your glucose by sampling your interstitial fluid which is the fluid just underneath the top layer of skin. Placing the device required a small amount of dexterity but once you do it the first time you get the hang of it. The needle or probe is 0.5mm thick and you barely feel it when it is attached. Once in place you do not really notice it.


Lasting Insights

It’s been around two months since I finished the experiment. Am I still cognizant of the lessons I learned? I’d have to say yes. It has hard wired in me the sensitivity I have to carbs which surprised me a bit when I first start seeing the numbers. I avoid my morning toast (previously a staple when I ate breakfast) and I’ve cut down on the corn tortillas during taco Tuesdays at our house.


After three months of use I learned 80-90% of what I needed to know. Could I have learned it in 1-2 months? Probably. Would it be nice to continuously monitor it forever? Not unless they figured out a way to make it less labor intensive to have to place in the data of what you eat. The pitch for January mentioned above is that they give you a report on the foods which spike your blood sugar so you only need a short period of data then you are set. It is an interesting concept.


Overall, wearing a CGM provided me with some valuable insights to change my behavior and new knowledge on my personal health and (hopefully) longevity.

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