Continuous Glucose Monitor

I’ve been wearing a continuous glucose monitor since 2020 in order to understand how different foods and activities affect my blood sugar.

Spikes in glucose can attract free radicals and cause oxidative stress. Elevated glucose levels also damage the endothelium lining your blood vessels, increasing the risk that apoB particle will get stuck and inflamed in it (see Cholesterol), which can increase your risk of cardiovascular disease, stroke and vascular damage.

My fasting glucose and HBA1C has always been very good – averaging 4.7 mmol/L (fasting glucose), 5.4 mmol/L (mean glucose over 14 day period) and 5.0 (HBA1C), so I am of low risk of being diabetic at this stage. However, as I move away from a ketogenic diet and incorporate more carbs for performance, I wanted to better understand how different carbs affect my blood sugar, and how I can minimise any glucose spikes.

 

Which CGM to wear

In Singapore, the most commonly found CGM is the Abbott Freestyle Libre Sensor. You can buy it without a prescription from any pharmacy or from Amazon SG with free same day delivery. It costs the same either way ($102.15 after GST as of July 2023). The Dexcom G6 is also available online.

 

Unit of Measurement

• UK/SG uses mmol/L
• US uses mg/DL

To get from mmol/L to mg/dL, you need to multiply by 38.67. To get from mg/dL to mmol/L multiply by 0.02586. (Can you see my eyes rolling.) No idea who’s smart idea it was to complicate things by creating two different units of measurement, but there are many conversion tables out there to help you toggle between the two units of measurement.

 

Inserting the CGM

It’s not painful at all. Just take a deep breath and shove it in.

The Freestyle Libre doesn’t tell you this but in my experience (and based on other people I have spoken to), it’s best to have a shower, then scrub the area behind the arm to remove any dead skin and sanitize with an alcohol pad to remove any oil. This will help the CGM stick on better and last longer.

In terms of placement, I like to insert it into the fattiest part of the arm above the tricep. Try not to stick the CGM into muscle, because it becomes very uncomfortable.

The first time I wore the CGM, it stayed on for the full 14 days. The second/third time, with sweaty ashtanga yoga and arm balances, it would fall off before the full 14 days. Some people suggest using sports tape to keep it. You can also get a variety of sensor patches from Amazon, that help the sensor to stay on (e.g. Skin Grip or Flexd).

Here’s a little secret. If you call Abbott and tell them that the CGM fell off before 14 days, they will courier a new one to you for free.

 

Target Ranges

After getting the CGM, the first thing you want to do is to set your “Target Glucose Levels” in the app. This is the tricky part because different people/associations have ideas of what is normal.

• Singapore’s Health Promotion Board recommends fasting glucose of < 4-6 mmol/L or 70-110 mg/dL (ideal) or 6-8 mmol/L or 110-140 mgl/dL (optimal) and 2 hour post prandial glucose of 5-7 mmol/L or 90-130 mg/dL (ideal) or 7-10 mmol/L or 130-180 mg/dL (optimal). (Source)
• The American Diabetic Association recommends a target range of 70-180 mg/dL (4-10 mmol/dL) with blood sugar 180mg/dL after 2 hours of eating. (Source)
• Levels Health recommends maintaining glucose levels between 72–110 mg/dL (4-6 mmol/dL), limiting post-meal glucose rises to no more than 30 mg/dL (1.75 mmol/dL) from pre-meal levels, and maintaining an average glucose of 100 mg/dL (5.6 mmol/dL) or lower. (Source)

 

Generally accepted normal results fall within these ranges:

• Fasting: 3.5-6 mmol/L (60-100 mg/dL)
• 1 hour after eating: <11 mmol/L (<200 mg/dL)
• 2 hours: <8 mmol/L (< 140 mg/dL)

 

Attia prefers to see lower readings (in American units so mg/dL):

• Fasting: 90 mg/dL (< 5 mmol/L)
• 1 hour: <120-130 mg/dL (<7 mg/dL) depending on the amount of muscle mass one has
• 2 hours: 100 mg/dL (5.6 mmol/dL)
• Attia tracks how many times it goes above threshold of 7.8 mmol/L or 140 mg/dL

 

Personally, I try to follow these ranges.

mmol/L	mg/dl	Range
4.0	72	Ideal Fasting
5.0	90	Ideal Fasting
6.0	108	Ideal Fasting
7.0	126	Ideal 2 Hour Post Prandial
8.0	144	Acceptable Post Prandial
9.0	162	Acceptable Post Prandial
10.0	180	High Post Prandial – try to minimise
11.0	198	High Post Prandial – try to minimise

 

On the Freestyle Libre, my target range settings are as follows:

• In the earlier days (2020, 2021), I would set the target levels at  at 3.9 to 7.8 mmol/L (70-140 mg/dL)
• In Mar 2022, I set it at 3.9 to 6.1 mmol/L (70-110mg/dL) based on Level Health’s recommended settings – however, it is quite hard to keep post prandial glucose below 110mg/dL unless you’re on a ketogenic diet
• In 2023, I went back to setting the target range at 3.9 to 7.8 mmol/L (70-140 mg/dL)

 

 

Observations

My fasting glucose is about 4.4-5 mmol/L (80-90 mg/dL). Wearing the CGM, my average glucose throughout the two week period was about 5.2 mmol/L.

 

Exercise Induced Glucose Spikes

A regular paced walk would not affect glucose levels (4.8 mmol/L). This is usually done fasted.

A weightlifting session would bring it to 5.7mmol/L (55kg squat, max HR of 134bpm) and 7.5 mmol (80kg deadlift, max HR of 145bpm.)

A 100min vigorous and fairly intense ashtanga yoga session (mysore, intermediate series) brought it to 7.5 mmol/L. (Max HR of 127bpm).

Spin class at Crucycle would easily spike it past 9-9.5 mmol/L. (Max HR of 165bpm)

A fast run (at 6min/km pace) would spike glucose to 10.5 mmol/L. (Max HR of 174bpm)

Why? When engaging in high intensity, anaerobic exercise (requiring glucose and not fat for fuel), there will be acute glucose spikes as a result of the liver releasing stored glycogen to fuel the exercise. You will notice that these spikes fall very quickly (within 30 minutes). This type of glucose spike improves metabolic flexibility, glucose control and insulin sensitivity.

 

Food Induced Glucose Spikes

With a low carb / keto diet, it would be quite easy to keep post prandial blood sugar below 6.1 mmol/L. However, with any kind of carbs, it would spike it to 7-9 mmol/L after eating. The worst carbs for me were wheat-based carbs (pita, poh piah, bread). My blood sugar would also normalise very quickly, and within 1 hour it would be back to 5 mmol/L.

Here are some examples of food induced glucose peaks for me.

No impact

• Dark Chocolate with Sea Salt: 5.1 mmol/L
• Fish soup (no rice): 5.1 mmol/L
• Chia Pudding with 1 scoop Heal Vegan Protein: 5.1 mmol/L
• Salmon and broccoli: 5.1 mmol/L
• Ben and Jerrys New York Super Fudge Chunk: 6 mmol/L
• Soy flat white: 6.1 mmol/L
• Heal Vegan Protein (2 scoops, 25g): 6.2 mmol/L
• Half a finger of sweet potato with cod and veg: 6.5 mmol/L
• Baked cheesecake: 6.6 mmol/L

Minor Impact

• Organic cocoa with lots of stevia and a scoop of walnut/cashew powder: 7.2 mmol/L
• Nasi Lemak: 7.4 mmol/L (not as high as I would have expected, possibly due to high fat content)
• Mee sua (one bowl): 7.5 mmol/L
• Oatmilk flat white: 7.5 mmol/L
• Brown rice (two big spoons or 1/2 bowl) with veg, chicken, egg, prawn: 7.7 mmol/L

High Impact

• White fish beehoon soup (one bowl): 8 mmol/L
• Rolled oats with banana and honey: 8 mmol/L
• (Shared portion of) Pancakes with maple syrup and fruits: 8 mmol/L
• Efu noodles with honey pork ribs and century egg spinach: 8.9 mmol/L
• Brown rice (two big spoons or 1/2 bowl, with veg, towgay, tofu, and 3 sui gao dumplings): 9.7 mmol/L – suspect the sui gaos are also high carb
• Half a poh piah (2 pieces): 9.8 mmol/L (this really surprised me!)
• Banana: 10 mmol/L
• Pita bread and one pita bread folded cheese burger from Miznon: 13 mmol/L (this was the highest spike I ever saw but could also be because I stuffed my face with free flow pita bread before the meal)

Note that this is very individual and will not be reflective of how these foods may affect your blood sugar. The same food can also show a different glucose profile if you exercise before, or change the order in which you consume the food.

 

Reactive Hypoglycemia: If I eat a meal that is very high in refined carbs (e.g. a lot of white rice or noodles) and experience a very big glucose spike, I would sometimes notice a big crash and overcorrection, where my glucose levels would drop below the initial levels and even drop to hypoglycemic levels (<3.9 mg/dL). This would often result in me feeling super sleeping after a meal and crashing hard or passing out on the couch.  Perhaps I have an oversensitive pancreas and over-secrete insulin (speculation, though my fasting insulin levels are normal).

 

Regulation of Ghrelin and Leptin Hormones: I have also noticed that if I eat a lot of carbs (or sugar), I feel hungry and have cravings all the time. One explanation is that ghrelin (the hormone that makes you feel hungry) is secreted to prevent hypoglycemia (blood sugar from dropping too low). Since I notice that I may have reactive hypoglycemia, it also makes sense that I have more hunger pangs as a result. Hence I have decided that it is better for me to keep my blood sugar relatively constant in order to avoid the increased hunger and cravings as when it spikes and overcorrects.

 

Alcohol Induced Glucose Spikes

Wine would cause my glucose levels to drop. Cocktails would cause it to rise slightly, depending on how much I drank.

• Wine: no impact
• Apperol Spritz: 7.3 mmol/L
• 3 Negronis: 9 mmol/L

 

Nocturnal Glucose Readings

What surprised me was that my nocturnal glucose readings would drop very low (below 4mmol/L, especially if I drank alcohol). This is because the liver releases stored glycogen as you sleep and if it is taxed with alcohol, it cannot release stored glycogen.  This nocturnal hypoglycemia could be a reason for frequent wake ups. I try to avoid excessive amounts of alcohol too close to bedtime for this reason. Day time drinking FTW!

 

Dehydration

I also noticed that when I did not drink enough water for the day, my average glucose levels would be slightly higher than normal. Why? Dehydration causes a hormone Vasopressin to be released, which signals to the kidneys to store water and for the liver to release glucose.

 

Stress / Cortisol Induced Glucose Spikes

Stress would also cause my blood sugar to spike (small spikes) due to the release of cortisol. However, in the long term, if you are constantly stressed and your cortisol levels are always elevated, this can result in a long-term increase in average blood glucose levels.

Interestingly, doing dropbacks during my ashtanga sessions would spike my glucose to 7.5 mmol/L – very likely cortisol induced because doing dropbacks used to scare the shit out of me, and would definitely spike my cortisol levels (and my glucose levels!)

 

Illness Induced Elevated Glucose Levels

In 2023, I stuck on a CGM after four days of gastroenteritis. To my shock, my average glucose was 1 mmol/L (~20 mg/dL) higher than normal at 6.3 mmol/L (it is usually around 5.2 mmol/L), with post prandial spikes having a much larger area under the curve. This is normal, as the body is dehydrated and epinephrine (adrenaline) levels are elevated to fight the virus.

 

Reducing Glucose Spikes

There are certain things that can be done to reduce glucose spikes

1. Drink apple cider before (or after) eating a high carb meal (before is better)
2. Plan your high carb meals around exercise (before or after are both good for regulating glucose levels)
3. Eat vegetables, proteins and fats before carbs to slow down the digestion of carbs. This will also reduce the spike
4. Walk after meals

 

 

References

• [PAYWALL] #165 – AMA #24: Deep dive into blood glucose: why it matters, important metrics to track, and superior insights from a CGM
• How a CGM can help you find your optimal diet and lower blood sugar – Levels Health
• Hyperglycaemia: Monitoring Blood Glucose – Health Hub / HPB
• CGM & Time in Range – American Diabetes Association
• Conversion Table for Blood Glucose Monitoring