• Top 8 Insights from a Continuous Glucose Monitoring (CGM) Device

    I’ve been curious about continuous glucose monitoring (CGM) devices for a few years. People normally associate these devices with diabetics, but awhile back there were indications that they would become available for non-diabetics. It did occur, CGM devices are now available to non-diabetics.

    A great question is why should you care about monitoring your glucose if you’re not diabetic? There are several reasons you might be interested in monitoring glucose:

    • Continuously high glucose is associated with several diseases. Understanding which foods or combination of foods drives your glucose high can help you adjust your eating habits.
    • To gain insight into how your body responds to different foods. A study published in 2015 that followed 800 people showed that every body’s response to the same food can be very different. (At this study link, there is a useful video and more details on the study.)
    • Eliminating glucose spikes and crashes helps you feel better.
    • Learn how to fuel during training and races for optimal performance. Sometimes athletes eat too much, sometimes too little. Wouldn’t it be nice to know how to fuel for optimal performance and eliminate gastrointestinal distress during races? As a sidenote, CGM devices are currently banned by the international governing body for cycling, the Union Cycliste International (UCI.) (See page 59 here, rule 1.3.006bis )

    With that background, I decided to wear a CGM device last summer. I was quite surprised by a few things that the monitor revealed. Here are 8 of my personal insights.


    1. Two slices of gluten-free bread eaten with eggs spiked my glucose.

    First know that I do not have a gluten intolerance, I just found a gluten-free bread that I liked to eat because of the size of the slices and the taste. During the first week of wearing the monitor I had a breakfast of two eggs cooked in butter, two slices of gluten-free bread with butter, and a small amount of cherry preserves. I had bites of each in random order. This breakfast shot my glucose up to 151 mg/DL. (It is recommended to keep glucose levels below 140 mg/DL for non-diabetics.)  

    At a breakfast a few days later I had two eggs, one slice of the same gluten-free bread buttered and with preserves. I ate some of the eggs first, then ate the toasted bread near the end of the meal. My glucose after this meal was only 122 mg/DL. I did two things differently in this meal. First, I limited myself to one slice of bread. The second was that I ate much of the protein first.

    1. The order in which I consume food impacts glucose levels.

    In item number 1, above, on the second breakfast I mentioned eating most of the eggs first. Researchers at Cornell University found that if diabetics ate vegetables or protein before carbohydrates, blood glucose was lower for the same mixed meal.

    1. Type of bread and number of slices matters

    Eating one slice of gluten-free bread/toast for breakfast won’t spike my glucose over that 140 mg/DL mark.

    I decided to experiment with different types of bread. A turkey and cheese sandwich using two slices of Ezekiel bread only peaked my glucose to 105 mg/DL.

    1. Exercise food timing matters

    I was on a week-long bike tour and had a turkey and cheese croissant sandwich with potato chips and got back on my bike to ride. Glucose only spiked to 125 mg/DL. Croissants are very high in fat, so this may have affected the glucose reading as well.

    On the same tour, I had ¾ of a turkey and cheese sandwich on a white hoagie bun with potato chips and I achieved an all-time high glucose reading of 219 mg/DL. I ate this sandwich after a short ride and did no exercise after eating.

    A few weeks later, I had half of a Subway 6-inch sub on white bread and some vinegar and salt Pringles. This lunch was consumed at about 6.5 hours into a very long ride and I rode another 1.5 hours after lunch. Glucose spiked on the chart to 147 mg/DL, but not nearly as high as eating a similar sandwich and not exercising after.

    1. Doses of Vitamin C, in excess of 500 mg can give false readings of high glucose

    Sometimes I consume a flavored drink packet that contains 1,000 mg of vitamin C and the CGM will show a spike as high as 140 mg/DL. This is a "false spike" is because the Vitamin C is affecting interstitial fluid – what the CGM measures – and not blood glucose levels.

    I could either reduce the vitamin C dosing or ignore the spikes.

    1. Bananas and Clif Bloks used during exercise spike my glucose more than I expected

    I was on a bike ride and decided to eat an entire small banana. It spiked my glucose reading up to 173 mg/DL. I think I could get the response to be “less spikey” if I ate the banana in smaller pieces over the course of time, rather than all at once. But…eating it all at once is far less messy.

    When I was on the bike tour, I noticed that every time I ate one or two Clif Bloks, it caused a glucose spike. Spikes would range from 130 to around 145 mg/DL. I wasn’t surprised that glucose spiked. After all, Bloks are very simple carbohydrates.

    A couple of days after the bike tour ended, I did a local race that took about 2:40 to complete. Due to the start time, I didn’t have breakfast before the ride and fueled with Clif Bloks. I consumed 5 Bloks during the ride and went well above 140 mg/DL and stayed there for 1:10 after the race was over.

    While nitro-jet fuel (sugar) is good in the right exercise situation, the graphs lead me to question what fueling strategies, given different exercise situations, are best for me? I don’t want to consume excess sugars or calories if they aren’t going to good use. I want to optimize health and performance.

    1. Ice cream doesn’t spike my glucose as much as I expected

    Okay, this could be a bad thing because it’s tempting to classify ice cream as “healthy.” That issue aside, regular high fat ice cream will send my glucose up to 130 but not higher than 140 mg/DL.

    1. Stress had a surprising effect on glucose.

    Driving to the mountains in Colorado up I-70 on a Friday afternoon in the summer is not a good choice, but sometimes it can’t be avoided. During the very stressful drive, while consuming nothing but water, glucose climbed from 105 mg/DL to 119 mg/DL. I could see the graph slowly increase over the course of the drive. Stress and cortisol increase glucose response.


    Using a CGM was very educational. I was able to watch my own body response to foods as well as compare glucose responses to a few of my buddies. It is interesting to see that our glucose responses to foods was often similar and also often different.

    This is a technology I will be watching as I can see applications for overall health and athletic performance.

  • ← Next Post Previous Post →
  • Leave a comment