If someone offered you an opportunity to take a peek under the hood of your engine, would you take it? A chance to see the ebb and flow of the body’s physiology throughout the day? To observe the dynamic changes the body’s systems undergo while trying to maintain a steady homeostasis?
Hell yeah!
I have joined the group of non-diabetic curious people who have plugged themselves into a ‘continuous glucose monitor’ (CGM).
What is a CGM and what does it do?
A life-changing tool for diabetics, a CGM is a sensor applied to the skin which measures the amount of glucose in the interstitial fluid found between cells in a tissue. It uses a small, flexible needle that pokes through the skin and is commonly sited on the back of the arm or the abdomen. The sensor holds about 8 hours of recording time, sampled in windows of one minute. This information can be transmitted via NFC to either a hand-held glucose monitor or to a blood glucose monitoring app on a NFC-enabled mobile phone.
I am not diabetic, so I don’t rely on the CGM to tell me if my glucose is poorly controlled with rocketing highs. I don’t need to know if my HbA1c is elevated. I don’t need a life-saving notification if my glucose falls too low.
CGMs provide new insights into Blood Glucose Trends.
What the CGM does give me is an insight that no-one previously had before, unless they were in a lab experiment or Intensive Care Unit and attached an arterial cannula to sample blood. Otherwise, they would have to use painful finger-prick capillary glucose strips throughout the day – but even those with the highest requirement for measuring frequency wouldn’t take samples on the minute.
For me, having a real-time glucose sensor allows me to see daily patterns of blood glucose excursions. Blood glucose is a product of multiple variables including the status of insulin sensitivity or insulin resistance, diet composition, exercise, sleep and stress. As a tool for type 1 and type 2 diabetes, CGMs can be invaluable. When used as a lifestyle medicine tool, to build awareness about the effects of our daily actions on our health, and perhaps to prevent chronic metabolic disease, a CGM can also provide useful insights. Wouldn’t you want to know, to be empowered to engineer your health?
People with diabetes can get the sensors on the NHS for free. As I am not diabetic, I bought my own. I am using a Freestyle Libre. The sensors themselves are not cheap and can retail for more than £100 (although can be cheaper elsewhere), which is an expensive price for a product that expires after two weeks of use. I hope the financial cost, however, will be money well invested – in a device that could provide a wealth of data about lifestyle and health, as well as prodding my curiosity buttons. Other people have used CGMs in similar circumstances to me. Here is one example but I am sure there are other stories to be found.
Why now is the right time for me to use the CGM for a blood glucose experiment.
I have had the CGM stored in a box for a couple of months now. I wanted to choose the right time to use it. As it was quite expensive, I didn’t want to waste its potential with a poorly planned window of time. So, why use it now?
It turns out that the next two weeks are a perfect opportunity to measure my ‘normal’ life and compare it against an upheaval in my routine – a contrast that might provide interesting information about the interactions between my physiology, my lifestyle and environment. Indeed, we learn a lot about health at the extremes of physiology.
I have been working in a General Practice (GP)/Family Medicine practice, but my time is coming to an end. It’s been a busy four months of seeing the general public in one of the corners of Bristol. Although challenging in its content, the day-time working hours have allowed me to have a life that has been incredibly regular and not seen before during my (short) medical career.
No weekend shifts, no late-nights in the hospital, no night shifts. I have been a pretty normal individual. I have had the luxurious ability to eat breakfast, lunch and dinner at the same time every day. I have hours after work I can call free time and I can plan my hobbies, sports and social events weeks in advance.
It is a pretty wonderful circumstance to be in and I can see why so many doctors are persuaded to become general practitioners, to seek part-time employment or even to move to non-medical careers that provide flexible control of free time.
Right now, I have a ‘Normal’ Environment and Lifestyle.
The regularity of my lifestyle is key to the first part of my CGM experiment – when looking for patterns in the storm of a person’s life, I envision great difficulty if the cornerstones of food, sleep, exercise and daily activity are variables that are continually moving. Correlations would be very hard to draw. I’m using the CGM during my last week of my General Practice job to measure what a ‘normal’ life looks like as best I can (with some small experiments thrown in).
What is interesting about normal?
- My glucose overnight when sleeping. How low do I (my sugars) go?
- My glucose just when I am about to wake up in a fasted state (A suggestion of stress and of insulin resistance).
- The effect of breakfast on my blood glucose.
- What about variations on a breakfast? E.g. porridge with/without peanut butter.
- What about different types of breakfast? E.g. Porridge versus eggs.
- The effect of my daytime activities, including commuting and working.
- Does my lunch affect my blood glucose?
- Does the post-lunch nap correlate with changes to my glucose?
- Do I have low glucose when my stomach rumbles? Or, am I hypoglycaemic when I am hungry?
- What happens to my glucose when I exercise?
The experiment is in full swing (I started on Tuesday and it is now Friday). I’m sitting on my couch because I have eaten a ‘control’ breakfast of porridge and am seeing if my glucose response changes by being sat down all morning to write, rather than commuting by bicycle to work. See, how interesting is that!?
Next Week is Abnormal: Long Days and Night Shifts.
The CGM is useable for two weeks, while I only have one week of working in a General Practice with a ‘normal’ lifestyle. What does next week hold?
Next week is full of changes.
Next Wednesday I will join a busy surgical team in a big hospital, a departure from my current daytime 8-5 bliss. I start this job by working 13 hour night shifts – a change that might have measurable effects on my physiology.
Everything will be changed from my life at present – breakfast becomes dinner, lunch becomes a midnight snack, I will work in the zombie-land of a nocturnal hospital and I will sleep in the land of the living. In a way, this period of lifestyle disruption allows me to act as my own ‘control’ – I am measuring normal physiology before switching to measure an extreme state of physiology.
As a rough summary:
Week 1: Daytime living, regular sleep, exercise, activities and food.
Week 2: Nighttime living, irregular sleep, sparse exercise, few activities, irregular food.
The aim: To understand more about how blood sugar is affected by lifestyle factors, by comparing readings taken during normal day time living against those taken during the physiological stress of night shifts and hospital work.
I have a few very basic observations in motion already.
The Porridge Experiment
Over three days I have eaten porridge for breakfast, which, alternated with eggs, forms a staple in my breakfast rota. As I eat porridge regularly, I want to know what the porridge breakfast does to my blood sugar. Moreover, how do the toppings I add to the porridge affect my blood sugar?
I followed my normal recipe of oats and toppings. I used 65 grams of porridge oats from Lidl, soaked overnight and cooked on the hob. My toppings include 10g of sunflower seeds, half a banana and half an apple. I add 1.5 scoops of whey protein to the porridge. I also add a heaped tablespoon of crunchy plain peanut butter which amounts to 90g.
I planned to exclude the peanut butter, the considerable source of fat, to see if my glucose behaved differently. I also planned to see if my glucose jumped if I wasn’t physically active after eating a carbohydrate dense breakfast.
I didn’t add anything like cinnamon, which has effects on blood glucose. I even drank decaffeinated coffee, just in case the caffeine has any subtle effect on my glucose disposal or gluconeogenesis!
Day 1: Normal oats, banana, apple, seeds. No peanut butter. Increase whey protein to two scoops to compensate for protein lost by excluding peanut butter.
Day 2: Normal oats, banana, apple, seeds. Normal peanut butter (90g). Normal whey protein.
I then got on my bike, cycled to work for about 20 minutes and sat at my desk. I measured my glucose.
Day 3: Normal oats, banana, apple, seeds. Normal peanut butter (90g). Normal whey protein.
Today I have the day off, so I didn’t have to commute. Instead, I am ‘simulating’ a sedentary lifestyle, sitting or standing at my desk writing this blog.
Results to follow at a later date..
N=1 Experiments are fun but not robust.
OK, I admit, this is only a two day experiment and has lots of room for error. Have I controlled for all variables? Absolutely not. Will I gain meaningful data? Maybe but probably not! Should I repeat it? Yes. Will I? Definitely.
I am excited by my small n=1 experiment and looking forward to seeing how things unfold! I may have been foolish by trying to fit so many lifestyle changes in during one small window. The potential experiments and data collection is going to be huge – so retaining perspective will be challenging. In the future, perhaps I will just focus on one variable to a deeper degree.
Even if no meaningful data comes out of this experimental period, having a constant window into my physiology has given me many useful insights, surprises and has stimulated my curiosity.
What do you think?
What further experiments would you recommend?
P.S. I wrote this using Workflowy. It’s an excellent note-taking app as I find its user interface much more intuitive and mind-friendly. It’s free. Check it out by following this link.
Dr Rory Heath 
[…] For a two week period between November and December 2019 I used a Continuous Glucose Monitor (CGM) to measure my blood glucose. You can read about the concept and the experiments I planned in the blog I wrote at the time. […]
[…] With so many people concerned about the negative health consequences of high carbohydrate diets, I thought it would be interesting to see what the effect of my daily bowl of porridge would be on my blood glucose. […]
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