CGMs – The Performance Device That Could Be Your Game Changer

First off, let me explain what a CGM device is.  CGM stands for Constant Glucose Monitor. These devices, and finger prick tests, have been used for years to test blood glucose.  People with Type 1 diabetes have been able to use them to avoid, or limit, painful finger prick tests, and now their application is available to us as athletes!

After reading the New York Times Article, “Can Technology Help Us Eat Better” I was intrigued.  The author of the article wrote about how he used one of the new Apps that uses AI to review his body’s response to various foods, and then made suggestions on how to improve.  You see, we have all heard “Sugar is Bad”, but many of us don’t really understand what to look for with metrics, what constitutes “bad”, and ultimately, how blood glucose and insulin affect our bodies.  As a performance athlete and data driven coach, I Want To Know!!

So naturally, I guinea pigged on myself.  It’s helpful having a PhD Nuclear Physicist in the house, and he helped me set up my own CGM test to monitor my blood glucose.  He explained it’s very important to document EVERYTHING.  This meant documenting what I ate daily and when, my workouts, how I felt before, during and after, and checking the CGM upon wake up, when feeling good, when feeling bad, before, during, and after eating and workouts.  And I learned A LOT!

These are the things I wanted to determine using the CGM, if possible:

  1. What are my blood glucose trends?
  2. Am I healthy? (My Doctor already said yes based on a 12 hour fasting glucose under 100 (more on that later) Am I optimally healthy FOR AN ENDURANCE ATHLETE?
  3. Which foods are my triggers to spike blood sugar?
  4. When I’m feeling low motivation, am I just tired, dehydrated, or need food?
  5. In long events (a 20 mile training run in my case), how does my blood glucose vary, and how can I keep it level using advanced fueling techniques?

Before I go further, let me explain that I have an advanced knowledge of exercise physiology, nutrition, and access to a remarkable Registered Dietician, Internist and Gastroenterologist.  Therefore, if any of this seems overwhelming or doesn’t make sense, rest assured of two things:

  • The new Apps are designed to do the work for you;
  • I’m here to help! Contact me!

In 2016 at the Endurance Coaching Summit, I attended a lecture that showed the various effects of certain foods on blood glucose, and how those reactions varied from athlete to athlete.  In the lecture, the presenter showed two graphs for two athletes. On separate occasions, Athlete 1 experienced a Blood Glucose spike after eating a banana, but almost no reaction after eating a cookie on a different day.  The same experiment was repeated on Athlete 2, BUT, this athlete did not have a Blood Glucose spike with the banana, but rather with the cookie, which is what many of us think of as “normal”.  Back then we only could test these things in the lab, but now we can test them on ourselves at home and watch what happens as we eat that banana or that cookie.

Based on the New York Times article, I went to the LevelsHealth website and proceeded to devour (pun intended) all of the information in their Blog posts, and then went down the rabbit hole reading the peer reviewed science articles I found there.    After reading all the information, I knew I wanted to try using a CGM to up my game.

As fate would have it, I was able to get into the program (also referenced in the NYT article) faster, so I went with that App.   Following was my experience. uses the Freestyle Librelink by Abbott. This is a 14 day CGM and the way it works for is, you wear it for 14 days paired with a Fitbit or Apple Watch.  You record everything you eat, drink, and do for exercise/workouts, and follow suggestions for mindfulness. There’s a lot more to it, however, it was clear on Day 1, that this is for Diabetics, and not for a performance athlete that is a serious foodie. The Librelink is awesome, only the wasn’t on par.  Why do I say that?  The first four foods I eat daily weren’t in their food library, couldn’t be located by barcode scan, couldn’t be found manually, and after emailing the company copies of all the info and them promising to add them, nothing, nada, zip.  They said to find something similar.  For Ancient Grains Seed Protein, their suggestion was Nature Valley Granola Bars.  At this point, I knew to go rogue and follow the LibreLink App.  Coincidentally as I’m writing up my findings on this, SuperSapiens has just come to my attention and I’m anxious to pursue their research and to continue this path.  Check back for an update to this article!

First was insertion of the CGM (and yes, there’s a needle, but you don’t usually feel it go in). sent along three adhesive cover patches to last the entire 28 days.  After 3 swims and 10 days of sweaty training and showers, the first started to come off, but the Librelink had to be pried off with baby oil after 14 days.

The website said you can’t check your Blood Glucose too frequently, but at least every 7-8 hours to get stored data. You can watch your trends for the last day, 7 days, 14 days, or 30 days.  Using the App I could see my heart rate data from workouts in a graph above my blood glucose data which was really important to understanding if I’d fueled effectively.   Here’s a sample scan in the moment:

Over the course of the next 14 days, I checked, monitored and adapted. I found myself more focused on the following:

  1. Avoiding snacking as follows:
    • I’d feel an urge for a snack and think I needed one. 
    • I’d check my Blood Glucose.
      1. If Blood Glucose going low or low, then I’d have a protein and carbohydrate snack;
      1. If Blood Glucose normal, then I’d hydrate, go for a walk, or take a nap as needed
  2. Fueling more thoughtfully before, during and after workouts as follows:
    • Check HRV for training readiness (ask Coach Clare how to do this!)
    • AM Workout – Check Blood Glucose and have a light breakfast with protein included;
    • During Workout if feeling “off” or sluggish, check blood glucose;
      1. If low, and a long workout, eat, then see if I can get blood glucose up.  Generally the answer was yes using glucose tablets and chews;
      1. If normal, then heading home and checking hydration levels. Watch for my upcoming article, “Are You Hydrated?  This little strip will tell you immediately!”
  3. Avoiding more than a snibble (.5 ounce) of 70% dark chocolate at night, or else having it earlier after dinner
  4. AND THIS IS KEY!  Walking after eating! This winter I completed the 7 Week Course with Stacy Sims, PhD who is one of the most recognized experts on Exercise Physiology and Athlete’s Hormones.  She explained how the Glut4 receptors are activated by exercise, and we can avoid blood sugar spikes and reduce Insulin Resistance (in healthy athletes) by going for a walk after meals.  It can be as simply as a 10 minute walk with your dog or kids up and down the street.  This means LESS FAT STORAGE and more blood glucose to your muscles! 

By using the CGM before dinner, after dinner, and after a leisurely walk with our 13 ½ year old dog, I’d watch my blood glucose rise and level and hold in a healthy range.  On nights we skipped the walk, it spiked up a bit higher. 

This is probably why Tim Ferris wrote in the 4 Hour Body that he does: Air Squats, Wall Push Ups and Band Pull Aparts 3 times a day around meals.  He’s keeping blood glucose levels moderated and decreasing Insulin Resistance (i.e. not storing fat and keeping his metabolism younger!)

As a competitive athlete (top 10-20% in long course racing), if you’re going for a sub 3 hour marathon, or looking to compete in Ironman or Ironman 70.3 distance events, then using a CGM on long training rides and runs can help you dial in your nutrition because you’ll know what your “normal” blood sugar is for long rides and runs at various intensities, and how what you’re eating and drinking during rides and runs affects your blood sugar.  Note – you want to keep it as level as possible, and knowing how to change what your eating throughout the event to keep it level requires lots of training, and a good Coach to guide you. (Need help with your nutrition? Ask Coach Clare Here for help!)

As an Endurance Athlete who is a mid-packer or a recreational athlete who is racing to be THEIR best, then a CGM not only during training is key, but all the time for a month as explained above.  Nail your everyday nutrition, optimize your lean body mass, fuel with what YOUR body needs and when, and you’ll find your engine and body optimizing for race day!

Have More Questions about how to use a CGM to Game Change Your Training and Racing? Leave a comment down below or contact me!