One of the benefits of working in the medical industry is that from time to time, you get to play with some cool toys.  Continuous glucose monitors (CGM) have been around for a few years.  They are now funded for Type 1 diabetics in NZ, so the local drug company dropped some off for my doctors and nurses to trial for 2 weeks.

In the past I’ve looked at heart rate monitoring, power monitors etc.  Most of the time, I don’t find it interesting or useful to continue.  I was glued (literally!) to my CGM monitor for 2 weeks!  I’m not diabetic (my HbA1c is 33) but it was fascinating.  Diabetes is classified as HbA1c 50 and above.  However, this doesn’t reflect day to day, or hour by hour fluctuations in blood sugar.  

My CGM is a basic Freestyle Libre 2, made by Abbott.  It attaches to your arm via a thin filament that comes out of a plastic disc.  Each disc costs NZ$106 and lasts for 2 weeks.  It runs on bluetooth, and gives you glucose readings each minute on a phone app.

The eye opening thing for me is how variable my blood sugars are after meals.  If you do a traditional finger prick blood sugar test after eating, you have no idea where on the curve the result sits. The blood sugar could still be going up, on the way down, or yet to rise!  I can see how useful it is for Type 1 diabetics, because they titrate their insulin to the blood sugars result.   Type 2 diabetics tend to start on oral agents, but if they are on short/medium acting insulin, it would also be very helpful.  It also provides an idea of how particular foods affect their blood sugars.

Back to this being a unicycle blog….of course I had to try it in training! The other big eye opener for me is the effect of exercise on blood sugar.  It completely flattened my sugar peaks.  
This is a day showing sugar peaks with meals.  I missed breakfast, and was mostly sedentary, seeing patients in clinic:

During my 2 week trial, I ate high carb and low carb meals, high GI and low GI, and they all resulted in a similar rise in blood sugar.  So much for the glycaemic index!

This is what happens when I exercise- the day I rode 265km for 12hrs (0800-2000hrs) for my practice 12/24hr record. 

I had oat porridge and coffee at 7am for breakfast.  My ride started at 8am, just when my sugars should be rising.  Instead, it remained flat, and stayed that way for 12hrs.  During this time, I ate a large cheese sandwich, 100g of chocolate, 3L of chocolate milk, 1 muesli bar, 1 apple, 1 1/2 meat pies.  They did nothing to my sugars. It was not until I went home, had a shower and dinner, that my sugars started rising.

The same effect happened on other days- if I exercise within an hour of eating, my blood sugar remains very flat.  The effect even lasts into the next day, when the sugar peaks are at lower level than I would expect.
Take home message- eat what you like (within reason), but exercise after eating to keep sugars low.   How this translates into long term health for non-diabetics is hard to know, but it seems to make the insulin/glucagon balance more effective.  That can’t be a bad thing.  

In terms of performance, I haven’t used it enough to make a sensible conclusion. I did notice a power drop after I had lunch (approx 12pm) during my 12hr ride, but my average sugars also dropped from the low 6s to the mid 5s.  Perhaps I didn’t eat enough, or there was a surge of insulin that drove the sugars down.  I might just have to do another CGM trial to find out!