What I Learned After Wearing a CGM for a Week

Kirsten Puskar MS, RDN, LDN, CDE/DCES – written Feb 22, 2020

As a dietitian and diabetes educator, I was offered a chance to wear a continuous glucose monitor (CGM) to experience the technology as my patients do. I was able to experience having a sensor stuck to my abdomen for 15 days and observe the varying levels in my blood sugar (blood glucose or BG) during that time.

The CGM system includes a hand-held blackberry-type reader with a small plastic transmitter sensor that fits into an adhesive sensor onto my abdomen. There are several types of CGM devices available. The sensor has a metallic thread which is applied/inserted just under the skin in the interstitial fluid, not into blood or muscle. You can observe your BG in real time using the reader or download the data to review a week or two of your BG data. There is a slight delay (0 -15 minutes) compared to finger sticks in real time.

At this time, I have no diabetes diagnoses and have a healthy pancreas, so I did not see large variation of my blood sugar levels, but it was a learning experience to see the range and timing of my BG changes, and how well the sensor stays attached through a variety of environments, wet and dry.

We know that the body reacts differently to carbs, proteins, water and exercise, but thanks to the CGM system I was able to see the ranges and timing for different typical meals. My typical resting BG was between 80-120, while awake and active 110-180 mg/dL. After starting a meal, it could rise to about 200 the first 30 minutes depending on the carbs, fluids, etc. Often after breakfast it reduced to 80, but if I skipped eating then it would rise to 130.

I experimented to see how different food, beverages and exercises could affect my blood glucose levels such as dark chocolate, jelly, drinking excess water or adding olive oil to meals. My diet is mostly vegetarian, so consuming chicken or fish appeared like a fat and slowed my absorption rate. So many inputs can affect BG – it was so easy to raise my BG and such work to reduce it!

I’ve found that a few “rules” of managing your blood sugar are not always true, at least for my body. My BG resting range was 80-140 mg/dL and up to 200 mg/dL as I started eating depending on the carb/fluids consumed. Desserts with a meal kept BG lower than having them an hour after a meal. Having carbs on an empty stomach really increases BG!

MYTHS:

1. BG typically drops during the night.

For many people, blood sugar can be higher while sleeping than within an hour after waking. After a pasta and pesto dinner my BG reduced to only the upper 130’s mg/dL all night, dropping to 90 after starting my day.

• This could explain how athletes “carb load” the night before an event. Interestingly, a high carb dinner or an active day would increase my sleeping BG (120-130). It doesn’t come down (to resting level 90 again) until 30 minutes after eating in the morning.

• Waking and having nothing to eat, my BG would originally drop to 90 first hour or so, then climb through the morning into the 130s again. Breakfast no matter how small keeps BG level in the low-normal range.

2. Protein and veg do not affect BG levels

Protein and non-starchy vegetable foods DO increase BG and rather quickly too. My BG would increase as quickly as 20 minutes after starting a meal and come back to normal range within another 30 minutes. These foods did not increase my BG as high as carb foods did.

3. High fat meals may delay the increase in BG

Meals not especially high in fats/oils (like pasta with pesto and asparagus) can delay BG increase as much as over 90 minutes, and takes much longer to reduce it, once it took two hours. It would reduce then increase again a few times before coming back down to resting range. I used water and exercise to reduce my BG those nights. I imagine that cheese pizza would magnify the effects.

4. BG levels below 80 cause hypoglycemic effects, below 40 causes unconsciousness.

After an evening meal and exercise within the hour, my BG could reduce to the low 60’s and I had no hyperglycemic feelings, perhaps feeling just a little sleepy while watching TV. I have had patients see me with BG in the 30’s and appear fine, maybe a little confused, so I gave them the appropriate carbs to continue our visit.

5. When you feel hungry, you have low BG, especially before meals

I found that my BG was consistent between regular mealtimes, until just before the meal – it was not uncommon that my BG would increase 10 mg before a mealtime and before eating. Although it increased at these times, I felt hypoglycemic - shaky, hungry and anxious. Once I ate, 30 minutes later it increased further as usual but then decreased back to resting level again - all within the hour of starting the meal.

I may have gotten a bit neurotic about food, water and my BG levels while wearing the CGM especially during Valentine’s Day weekend. I removed it after only 8 days to the delight of my husband and co-workers.

I hope you found this helpful. I found a great appreciation for what my patients with diabetes do to daily manage their blood sugar and health!