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Insights from 45 days of wearing a Continuous Glucose Monitor (CGM)

Welcome to my blog post #4 describing my foray into the world at the intersection of medicine, genetics and technology.

This is a continuation of my last newsletter where I promised I would share some initial learnings I have had with my Continuous Glucose Monitor (CGM). As a quick refresher, the CGM is an FDA approved device made by a number of different manufacturers that you can install on your body where it stays on 24 hours, 7 days a week, for about 10 days at a time. A CGM works through a tiny sensor inserted under your skin, usually on your belly or arm. The sensor measures your interstitial glucose level, which is the glucose found in the fluid between the cells. The sensor tests glucose every few minutes. A transmitter wirelessly sends the information to a monitor (or on the phone in the case of the Dexcom G6 model I use) every 5 minutes. This provides 288 data points a day on my blood sugar level and can be correlated directly to my exercise, diet and sleep patterns. As an aside, the oft-mentioned A1c metric, which is the 90 day average of the blood sugar levels, has the following equivalence: an A1c of 6 is equivalent to an average 126 mg/dL level over that time period. All the blood sugar quantities are in units of mg/dL from here on.

I had the CGM on my body for about 45 days and here are some of my observations. I should stress that I am not a medical doctor but rather a “google doctor” i.e. I do most of my research on Google and every time I meet an actual medical doctor, I pick their brains incessantly to come up with explanations for my findings. I don’t always find a reason in the literature or in my discussions for the observed phenomena so I will share them in this post and I will leave it to the doctors and nutritionists among you to provide the medical or scientific rationale behind it. My primary care physicians in the US have expressed an interest in learning more about my data because this is an unprecedented level of real-time data that potentially holds the key to personalized diet plans for better health outcomes. So here goes:

1. I had a small cup of strawberry ice-cream one evening, having not eaten for a few hours before that and, as expected, my blood sugar shot up from about 120 to about 190. A few days later I had dinner that started off with a small Caesar salad, followed by an entrée including shrimp and spinach, and ended with a small cup of strawberry ice-cream (same brand and amount as the earlier cup). My blood sugar level before I started my dinner was about 125 and, about an hour after I had my ice-cream, had gone up to 135. This was very surprising to me (and I was also excited because I had figured out a way to eat my favorite strawberry ice-cream without feeling guilty about it) and so I did some research to see if there was a logical medical explanation for it. As per Mayo Clinic’s website, fiber — particularly soluble fiber — can slow the absorption of sugar and help improve blood sugar levels. Soluble fibers, which dissolve in water, are found in oats, peas, beans, apples, citrus fruits, carrots, barley, among others. (read more on this at https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/fiber/art-20043983). In the first case, I had no fiber intake before the ice-cream but in the second case, I had spinach, which contains a healthy 2.4 g of fiber, which is 10 percent of the daily recommended intake, in a 100 gram serving. For a good reference on fiber content of the various foods, check out https://www.helpguide.org/articles/healthy-eating/high-fiber-foods.htm. This helped explain the difference in why my body reacted so differently in the two cases. 

2. My wife had cooked some okra (bhendi) and chapatis for dinner. I decided to forgo the chapatis and instead mixed the okra (bhendi) with yoghurt and had that as my dinner. I also had some avocados with truffle salt to round off the meal. This turned out to be quite a winning combination. When I started my dinner, my blood sugar was at 109. Seventy-five minutes later it had only gone up to 113 and then it stayed in the 105-108 range all through the night, going down to 97 by the morning. It was one of the best nights in terms of my blood sugar level in spite of enjoying a meal that I found tasty and therefore sustainable. If I can stick to this type of blood sugar pattern, I can bring down my A1c to the 5.5 level from the current 6.0. On researching okra, yoghurt and avocado, I found that each of them had blood sugar level reducing effects:

  • Avocados are low in carbohydrates and sugar, both of which are critical to controlling blood sugar levels. In fact, according to the USDA, one cup of avocado cubes weighing 150 grams contains 12.8 grams of carbs, less than 1 gram of sugar and 10.1 grams of fiber…truly a superfood. 
  • Evidence of okra having anti-diabetic properties is relatively limited but in one study, published in 2011 in the Journal of Pharmacy & BioAllied Sciences, researchers in India found that diabetic mice, fed dried and ground okra peels and seeds, experienced a reduction in their blood glucose levels, while others showed a gradual decrease in blood glucose following regular feeding of okra extract for about ten days. Okra, similar to avocados, contains small amounts of carbs and sugar and a healthy amount of fiber: 7.5 g of carbohydrates, 1.5 g of sugar and 3.2 g of fiber.
  • Yoghurt is low in carbohydrates and high in proteins and therefore is known to not cause blood sugar spikes. Besides, it is a great source of probiotics, which helps gut health in general.

3. One of my favorite breakfast foods for some time now has been an açaí bowl with some fruits and a banana puree. I had read about the health benefits of the açaí berry, given the reasonable fiber content and vitamin A, and I found the açaí bowl to appeal to my taste buds. However, what I hadn’t realized was that the açaí berry isn’t naturally very sweet and so a reasonable amount of sugar is added in to the açaí bowl to make it more palatable. I started the morning with a blood sugar level of about 110, but an hour after consuming the açaí bowl I had gone up to 140, which in itself wasn’t terrible. However, what I found interesting is that it remained at the 140 level for almost six to eight hours after that, which was unusual. I need to repeat this experiment a few times to deconvolve effects from exercise and anything else I may have done. I need to figure out with the café if I can get them to reduce the added sugar and see if it still remains as appetizing, while dropping the blood sugar level more rapidly. This is work in progress.

4. This next observation is around the surprising result I got when I checked my blood sugar trend after I played about 90 minutes of soccer. Before I started warming up, it was around 115 which is where it stayed for the next fifteen minutes or so. Once the actual game kicked off, the amount of start and stop running increased dramatically, with the heart rate during the game going from the eighties to the one hundred and sixties. When the game was over, I checked my blood sugar trends over those 90 minutes and I saw that it had spiked to about 200, and then in the hour after the game was over, had dropped to the 140s and down to the 120s another hour after that. This unexpected observation sent me scurrying to the web to investigate. I found a site relating to blood sugar levels during soccer games (https://www.diabetes.co.uk/sport/football-and-diabetes.html) which mentioned, “Short sprints can stimulate glucagon release which raises blood glucose levels. Therefore, if your activity in the game consists mainly of short sprints with a low level of activity in between, it is possible to finish a half of football with higher blood glucose levels than at the start of the half. This effect can vary from person to person”. Glucagon's role in the body is to prevent blood glucose levels dropping too low. To do this, it acts on the liver in several ways: It stimulates the conversion of stored glycogen (stored in the liver) to glucose, which can be released into the bloodstream. Interestingly, when I do my gym routine that involves some light weights and mostly biking at a continuous pace of 3 minutes per mile, I do not see any such spikes in my blood sugar levels. The only conclusion I could reach is that the level of intensity in the gym was relatively constant without too many starts and stops and therefore the release of glucose into the bloodstream isn’t triggered as often.

I continue to have many more such observations daily, which I try to make sense of. I am beginning to get a better idea about the type of foods that I should eat and what I should avoid. I am trying to quantify and put into practice what “don’t eat too much sugar and reduce your carb intake” really means. This is the beginning of a long journey to learn more about how my body works and what is the ideal diet for me. And one that I am very excited about.  

Nickhil