What I Learned from Wearing a Continuous Glucose Monitor for 2 Weeks

As technology continues to take a more prevalent place in health and fitness, new devices and trends are always hitting the marketplace for those looking to optimize how they look, feel and perform. As a coach and trainer, I get asked all the time about the value of these things, so I not only like to do my diligence on the research and validity on each of them, often I will experiment with using it myself so I can provide first-hand feedback on the experience.

My latest experiment is with a Continuous Glucose Monitor or CGM.

The CGM is a small round patch that attaches to the back of your arm and is linked to an app on your phone. You can then check your current blood sugar levels by holding the phone up to the device to get real-time feedback on how certain foods or activities may be impacting your blood sugar levels.

After wearing the device myself for the last two weeks, here are 3 key takeaways that I learned from the experience:

1) The Impact of Certain Foods

I would check my levels after eating various foods to see if any created more of a blood sugar spike than others and it didn't quite match what I learned in school in my nutrition textbooks. Certain "good" foods created some of my biggest increases, including rice and blueberries. What was interesting however, is that when I tried those same foods again, but mixed them with a fat and/or protein, such as nuts with the blueberries, it did not have the same spike, which does support something that I have I always preached to my clients about having a mix or macronutrients with all meals and snacks and avoid eating carbohydrates by themselves.

Now, to the contrary, foods that would supposedly rocket my blood sugar did NOT. I tried red wine and cookies (all in the name of science and a testament to the level of sacrifice I'm willing to take for my clients), and my numbers stayed steady. As enticing as that would be to make believe that these could actually be GOOD for me, we need to do our best to not completely abandon common sense :

2) Metabolic Flexibility

Metabolic flexibility describes the ability of an organism to respond or adapt according to changes in metabolic or energy demand as well as the prevailing conditions or activity. Poor metabolic flexibility has been linked to obesity and type 2 diabetes.

Do you know someone or do you yourself go into a tailspin if you eat certain foods or go too long without eating? These could be minor signs of poor metabolic flexibility.

Thankfully it seems like I have developed a relatively high level of adaptability and metabolic flexibility as my levels never really went up or down more than 15-20 points in either direction, regardless of what I did or ate, with one exception that I will talk about next.

3) The Impact of Exercise of Blood Sugar

I would also check my levels after my training and had some interesting findings. The reaction to strength training was a spike equivalent to most of my meals and quickly returned to normal within the hours.

It was my cardio training that was most interesting. When I did my low intensity Zone 2 Training, there was NO change. Not to get too deep into the weeds of Zone 2, but it is the highest level of effort you can do without crossing over what is called your "Lactate Threshold". This is when we transition from using primarily fat as energy to carbohydrate, therefore lactate is released as part of the buffering process of utilizing carbohydrates as energy. You see for us to use fat as an energy source is a slow and laborious process for us physiologically, which is fine when we are at rest or doing something low intensity, but when we need a whole bunch of energy right NOW, that is when we need to use carbohydrates, since they can be used most easily as an energy source.

So what does that mean?

To most accurately measure your lactate threshold it requires either checking your blood through a pin prick while you are exercising (not very practical) or having your oxygen consumption measured in a lab (also not practical and can be costly). However, If my blood sugar is staying constant when doing my Zone 2 workout, I can then infer that I was able to not tap into carbohydrates as an energy source and probably did not go beyond my lactate threshold.

Now on the opposite end of the spectrum, the one thing that did shoot my blood sugar up almost 40 points was an extensive high intensity interval session on the bike. The workout I did required repeat bouts at 85% of my max heart rate or higher for several minutes at a time (It's brutal). The numbers showed that my body needed all of the energy it could get to get through this and so it started pulling as much sugar into my bloodstream as possible.

The Net Result

Do healthy individuals need to stick a device normally reserved for diabetics in the back of their arm?

As with any wearable device, the data you collect is only as good as the decisions and changes you make based on it. The primary goal is to create awareness so you can see the impact of your activity, diet and lifestyle have on your physiology, whether it is a sleep ring, step tracker or heart rate monitor.

If you do decide you would like to experiment with one for yourself, there are several companies like Levels and others that offer the service of supplying the device and interpreting the data for you (generally they are not available to the public without a prescription).