Observations from a CGM newbie

I’ve just finished the first 30 days of a 4 month trial with a Continuous Glucose Monitor (CGM), and can offer the following observations. I’m using the Dexcom G6 as provided by Signos.

  1. The CGM’s accuracy leaves a lot to be desired. Dexcom makes it clear that the CGM isn’t intended to be used as a diagnostic tool, as accuracy in the +/-20% range. It measures glucose in your interstitial fluid, which correlates with, but isn’t the same as an actual measure of blood glucose level. The GCM is also subject to artifacts from positioning, pressure, sudden changes in temperature, etc. Users note that A visit to your doctor and A1c testing are recommended if you have concerns about your metabolic functioning.
  2. Take your sleeping position into account when you apply your GCM. In addition to potentially being uncomfortable, if your sleeping position puts pressure on the CGM, it can produce artificially low readings and generate low glucose warnings in the middle of the night. Lay down in bed with your pillow and pay close attention to which parts of your arm feel pressure from your head or pillow. Similarly, showers or saunas can cause artificially high readings.
  3. Given 1 and 2, you’ll want to invest in an actual blood glucose test kit ($20-40 at any drug store), to double check levels that seem out of line with expectations and to perform an occasional calibration.
  4. Sensors last 10 days, and many users note much higher variability on the first 24-48 hours after installing a new sensor. Don’t read too much into data from the first day or two of a new sensor, and rely on days 2-10 for more reliable data.
  5. Given all that, the CGM is still a very useful tool for training and learning more about your body’s unique reaction to different foods and activities. Like training to HR or estimated power, it isn’t 100% accurate, but it is much more useful than no data. In the past 30 days, I’ve learned a lot about how work/personal stress is impacting my blood sugar and performance, identified a few specific foods that were causing bigger spikes than I realized, and I’ve already gotten enough information to revamp my pre- and during ride nutrition.
  6. While weight loss wasn’t my primary goal in trying the CGM, I can absolutely see the value of a CGM for someone who responds well to data and constant feedback. Some of this could simply be from the additional food and activity logging promoting conscious eating rather than mindless snacking, but if it makes good results more likely, then that’s an added benefit.
  7. The one drawback to my personal plan is that while I have a very good idea what blood glucose levels I want to see through the day and over the long term for general health and weight maintenance, I haven’t yet found a good number for optimal blood glucose levels during a ride or during different types of efforts. I’m currently shooting for boosting blood glucose shortly before and during the ride to normal post-prandial levels, and trying to maintain those levels with some consistency, seeing a return to pre-prandial levels within an hour or two of finishing a workout.

Crux of the matter - the CGM seems to me to be an expensive but useful training tool, assuming the user has some familiarity with blood glucose, and can accept the levels of limited accuracy and high variability currently available.