CGM Study Results – Low-Carb Eating

I’ve discussed my glucose tolerance test data in two blog posts, The Dreaded Oral Glucose Tolerance Test and Third Time’s A Charm. Now, I want to start sharing some of the knowledge I have gained from wearing the continuous glucose monitor (CGM). Everything I will discuss will be related to how my blood sugar responded to the food I ate, not my feelings on the device, software, accuracy, or anything proprietary. I loved having the opportunity to participate in this research study and it’s really not my place to interfere with any of that. It is my desire that CGM devices will become available and affordable for everyone to utilize. I feel they offer so much insight to our individual response and would be beneficial to anyone trying to become healthier.

Takeaway #1: I was happy to see that eating low carb meals had a minimal effect on my blood glucose.

While that is likely common knowledge, the scientist in me appreciated the confirmation for my body. It didn’t even take long for my body to exhibit this behavior. As I previously mentioned, I was able to eat a low carb meal after the first glucose tolerance test and my blood sugar was very stable, actually stabilizing during the meal period. This is what I ate and the resulting effect on my blood glucose:

The next day (Day 2), my blood sugar had fully stabilized and I essentially saw no change in my blood sugar after eating low carb meals throughout the day. Below are my meals and blood sugar changes for breakfast, lunch, and dinner.




Takeaway #2:  I can maintain stable blood sugar while eating out and while entertaining at home.

I know I can maintain a stable blood sugar eating salads and home-cooked meals, but I didn’t know what the effect would be if I ate out or ate other people’s cooking.  I thought the glucose monitor would be an excellent way to test that.  I ate fast food, at a sit-down restaurant, and then had a potluck meal in a social setting.  My post-OGTT meal was Whataburger; breakfast on Day 2 was Waffle House; lunch on Day 2 was a Chinese Mongolian Buffet.  Dinner for Day 2 was our weekly life group meal from our church, which is essentially random homemade or procured items that I have no control over.  At each of those meals, I was able to eat low-carb, high fat without any problem.  Sure, I might have to order off the a la carte menu or ask for something special, but I can do that.  I might have to choose wisely and not eat what society deems as tasty, such as buns, french fries, fried rice, dessert, or sweet sauces.  I might have to pull the breading off of my chicken before I eat it, but it is possible to eat low-carb, high fat!

Takeaway #3: My body did an excellent job of restoring my blood sugar levels after periods of intermittent fasting during low-carb eating.

Overnight, there are a few places where data collection from my CGM stopped (the data completed dropped out), which I believe result from me being a crazy sleeper. Overall, my blood sugar was also stable during the night, but at one point, it appears my blood glucose dropped and my body restored it back to equilibrium. I suppose this could be from the signal being lost, but I don’t believe that’s the case due to the gradual change in glucose concentration.

The stable blood glucose continued as long as I ate low carb or when I fasted – I’ll share Day 3 and 5’s results, but spare you the picture overload! On these two days, like Day 2, every meal or snack I ate was low-carb (less than 15g of net carbs total).

On Day 3, I ate a low-carb snack (late afternoon) and then low-carb dinner (evening). My blood glucose was perfectly balanced throughout the day and night, with a minimum of 73mg/dL and a maximum of 118mg/dL. The dip in blood sugar occurred while sleeping and appears to be accurate due to the shape of the data.

Day 5 was similar; I chose to eat a late lunch and dinner, and my glucose over the 24-hours ranged from 64mg/dL to 117mg/dL. There were two dips in the data during this day. One occurred during mid-morning (after I skipped breakfast), where my blood glucose reached 69mg/dL before stabilizing. The other dip (to 64mg/dL) occurred while sleeping and also appears to be accurate.

Other days show similar results during my low-carb meals and snacks, but not every meal was purposefully low-carb. There was a definite response in my blood sugar when I ate foods with carbohydrates (these experiments will be explained in a later post). However, it’s important to note that during the first ten days of wearing the CGM, I was careful to allow my blood sugar an opportunity to return to equilibrium after eating any meal or snack with a higher carbohydrate content. There is only one time where I purposely loaded carbs upon carbs and that is when I tried to reproduce my infamous “Torchy’s Ice-Cream Experiment” after having a stable low-carb baseline going before the experiment.

Takeaway #4: My morning fasting blood glucose remained good when I consumed carbs in a controlled manner.

I also measured my blood glucose with my meter every morning. Excluding Day 2 (the day after the OGTT), Day 5 (I had a sugary margarita in the evening of Day 4), and Day 9 (the day following the “Torchy’s Ice-Cream Experiment”), my meter measured my blood glucose to be between 79-89mg/dL. On the excluded days, my blood glucose was 98mg/dL, 97mg/dL, and 94mg/dL, respectively, showing that higher carbs consumed on the previous day impact the next morning’s fasting blood glucose.

This is something I see in my historical blood glucose data. The better I eat, the lower my fasting blood glucose the next day. Usually values greater than or equal to 90mg/dL are indicative of late night carbs or overdoing it completely on the previous day.

Takeaway #5: I kept some ketones around for good measure when I consumed carbs in a controlled manner.

I measured my ketones every morning, and they ranged from 0.2-0.5mmol/L during this 10-day period, excluding Day 2 and Day 5, when they were not detectable (post glucose tolerance test and large sugary margarita; shockingly, they were detectable after the “Torchy’s Ice-Cream Experiment”). I chose to lower my standards during this 10-day period to accommodate the carbohydrate experiments that I intended to perform because I knew I would be eating more carbohydrate than usual. Basically, I just wanted them to be present and approach light nutritional ketosis.

My normal maintenance goal is for my ketone levels to be 0.5-1.0mmol/L (light nutritional ketosis). To achieve this, I eat mostly low-carb plus intermittent fasting to keep me burning fat, but not setting myself up for major fat loss. For comparison, during weight loss periods, I allow my ketones to reach optimal therapeutic levels (3.0-5.0mmol/L), and even a little higher during extended fasting, but there’s no reason for me to be so strict during maintenance and definitely not while experimenting with carbohydrates.

Takeaway #6: The dawn effect is real, but not as “big” as I thought it was.

I wake up most days at 4:45am; apparently my body knows this! Every morning around that time, I had an increase in my blood glucose to prepare me for the day. During the first ten days with the CGM, my blood sugar increased an average of 20.1mg/dL before I woke up (n=10, standard deviation 7.0mg/dL) and then decreased an average of 23.8mg/dL (n=10, standard deviation 10.9mg/dL). When I discuss the second 10-day period, you’ll see it’s a little different and I find that fascinating as well, but more to come later!!

6 thoughts on “CGM Study Results – Low-Carb Eating

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