Continuous Glucose Monitoring


By Ryan Bonney

A few months back, Josh and I were continually being asked by patients what those little white discs attached to the backs of our arms were.

Well, here is my long and drawn out response… but please stay with me – the information gleaned from these little white discs might just save your life!

The discs are continuous glucose monitors (CGM)readers that insert a probe into your blood serum and communicate your blood glucose level (BGL) to your smart phone for fourteen days consecutively.

A common retort to conducting this experiment was “…but you’re not a diabetic, are you?”.

Well no, I’m not, but it has been quoted that 90 percent of people with pre-diabetes (i.e. on the road to becoming a diabetic type 2) are totally unaware of their dysregulated insulin levels and rollercoaster glucose spikes.

And scarily, up to “70 percent of people who are prediabetic will eventually develop the disease” (within 4 years where there has been no intervention).

Prediabetes is a “health condition in which blood glucose levels are higher than normal, but not high enough to indicate a diagnosis of type 2 diabetes. Prediabetes can be halted or reversed with dietary and lifestyle modifications, including weight loss, exercise, and stress reduction.”

The following is a synthesis of research on the topic, and these ‘rules’ helped to guide my rationale behind the experiment…

1. “Post meal (post prandial) glucose response to identical foods varies highly across individuals”.

People can be classified as a “low, moderate, or severe glucotype”, depending how they respond to food types. The referenced study determined glucotype from the peak blood glucose recorded within a 2.5 hour post-prandial window. Individual responses to food types is a novel concept that is increasingly gaining acceptance as another more reliable diagnostic strategy. 

  • Low = a very low spike after eating (>4.27mmol/L)
  • Moderate = a spike to more than 5.33mmol/L
  • Severe = spiking above 6.77mmol/L (which occurs in 24% of the ‘normal’ population)

Daily fluctuations between 3.9-6.7mmol/L are common for 91 percent of the population. BGL generally peaks 45 minutes after having a meal, but within two hours glucose should be back to baseline levels.

“…glycaemic variability, more than fasting glycemia or HbA1c, predicts development of cardiovascular disease, possibly via oxidative damage causing endothelial dysfunction”

HbA1c is a blood test that reflects overall blood sugar control over the previous 3 months, giving an indicator of longer-term average blood glucose levels. If elevated, this indicates that levels are likely chronically elevated; leading to the aforementioned risk factors.

2. Pragmatic Guidelines for CGM Data 

  • Foods that spike your BGL >7.2mmol/L should be treated with caution (“sometimes foods”).
  • Foods that spike your BGL >7.7mmol/L (a prediabetic range) should probably be avoided.

3. Risk Factors

  • As blood glucose level rises above 6mmol/L (fasting), there is a linear risk increase for cardiovascular disease risk, and an increase in diabetic development risk.
  • As it breaches 2mmol/L (fasting), diabetes risk trebles.
  • Time spent above 7mmol/L (after eating) may lead to complications in several health domains, including pancreatic damage, nerve damage, and retinopathy.
  • Above 88mmol/L (after eating) has an associated elevated risk of developing cancer. It is important to reiterate though that naturally, blood sugar levels will reduce back to a certain level once absorbed in the normal/healthy person, and that this is a normal response. Whereas in prediabetes/diabetes without appropriate intervention levels may remain elevated for longer.

Prediabetes is defined as fasting blood glucose consistently at 6.1-6.9mmol/L, or by reaching >7.77mmol/L after meals. 

Diabetes uses the measurements of >7.0mmol/L and >11.1 mmol/L respectively.

My Insights

After scanning myself 120 times over the two weeks, I learned that my average glucose was 4.4mmol/L, which gives a Haemoglobin A1C (HbA1c) estimate of 4.4% – both very healthy levels.

I tried to scan at the same time every day upon waking to get an accurate fasting BGL. Mine was 4.2mmol/L (on average), which is certainly within the recommended guidelines.

I scanned just prior to my first bite, 60 minutes after, and finally two hours after every food I wanted to specifically test.

My BGL sat within a healthy (determined as 3.9-6.6mmol/L) range 81% of the time. Instead of dealing with too many (only 3%) HYPERglycemic events (i.e. BGL too high), I seemed to have more HYPOglycemic events (i.e. an intermittent dip in BGL); particularly between 9pm and 3am.

  • Drinking alcohol in the evening reliably gave me one of those glucose dips while I tried to sleep; often resulting in a restless sleep and higher body temperature (which is associated with poorer sleep).
  • Roasted sweet potato (by itself) served me a whopping 8.2mmol/L an hour after eating.
  • Muesli with full fat milk elevated and kept me at 6.6mmol/L two hours after eating.
  • A protein smoothie with a whole banana, took me to 6.7mmol/L an hour after drinking.
  • A high carbohydrate burger and chips took me to prediabetic land (7.7mmol/L) for over two hours! Not overly surprising I’d have to say…
  • A High Intensity Interval Training (HIIT) spiked me on several occasions to 6.2, 6.4, 6.7, and 7.1mmol/L during the session. Presumably this is my body desperately shuttling glucose to my muscles where it’s needed most! 

Most of my regular breakfasts, lunches and dinners had a negligible effect on my glucose; a confirmation that for the most part my diet is ‘dialled in’, and I won’t be knocking on diabetes’ door any time soon!

We used the Freestyle Libre sensor, which cost $92.50 for the fortnight’s use. It sends data to your smartphone via NFC, or to a separate reader if you don’t have an up to date phone. 

We have no affiliation with that particular company, but it seems to be the most user friendly and affordable option on the market at present.  

I am not an accredited dietitian and while I am passionate about measuring one’s health status quantitatively, our in-house dietitian, Tasha, is the person you should consult with before undertaking this experiment.

We would love to hear from you about any self-experimentation and lifestyle changes you have made as a result!