Anyone Tracking Blood Glucose?

Does anyone regularly track blood glucose who isn’t diabetic? I’ve just started both The Obesity Code (after the recommendation on the podcast) and Fung’s other guide book on fasting. I was wondering if tracking blood glucose with a meter is an okay proxy for insulin levels and sensitivity? The assumption here being you’re not diabetic or prediabetic – and by measuring blood glucose you can get a rough idea if your body is sensitive to insulin, and/or your diet is not likely to be causing crazy insulin spikes.

There are a few devices that will upload data via bluetooth and chart your levels. I was considering trying out intermittent fasting, and so thought blood glucose might be an okay data point to track? Or is this another data point not likely to provide much value and lead to analysis paralysis?

I was thinking to begin with, trying 16:8, which seems fairly easy and straight forward. Finish eating at 10PM, do my workout the next morning fasted (which I’m already doing), then not eat until 2PM.

The device I’m looking at also comes with strips for measuring ketones (although not really looking at going ketogenic, so maybe irrelevant).

Blood glucose changing much during exercise is mostly a myth. There are critical organs, such as the brain, that need glucose. If it were to fall much you would become comatose and die. Because of the non-ideal nature of being dead, glucose use gets prioritised to brain type stuff, rather than cycling muscles, so what happens is your muscles start using Free Fatty Acids & Ketones in its place.

There are only 2 ways a non-diabetic should ever have a low blood glucose:

  1. they’ve nicked insulin or drugs from a diabetic
  2. they have a rare type of Pancreatic Cancer that secretes Insulin

You may actually find the ketone measurements more useful. It’s not as rare as you probably think. Try measuring when you wake up before eating.


I’m also curious if anyone else has gotten any glucose measurements. I had some blood work done a couple hours after a medium effort 90 minute workout and my glucose was 42 mg/dL which seems pretty low. It hasn’t affected my workouts so I never looked into it but I’m still curious what others are at post-workout.

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Yes, I have on several occasions tracked blood sugar with a CGM sensor. Each time for 2 weeks continuously. Even wore it during races, for example a 12h race.

Mmmm … well … yes, sort of interesting (initially) but I haven’t found a real use for it actually. What was really new to me is how the body flushes the system with glucose when doing intensity. This is endognous glucose, not exogenous. On the other hand how it keeps glucose levels steady when doing 4 hours of endurance in a fasted state. I train a lot fasted and log about 15-20h per week. My base endurance is pretty strong which shows that I can do these rides without any trouble. I assume you bonk without this base endurance.

I used this with an app on my Android:

and here’s an example from my “monitoring campaign”. But fed.

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I haven’t in a while, but a few years ago I used one of my wife’s (she has type 1 diabetes) expiring Dexcom CGM sensors to track for a few days. Very little fluctuation, although I also never did any hard workouts while wearing the sensor so maybe that’d be different if I went longer/harder.

Some point soon I want to try it again, I just need to wait until my wife switches over to a new sensor and I can use her expiring one!

Yea, I’ve measured my blood glucose to do a baseline for some of the foods I eat. It becomes more apparent what meals are good for you when and when you aren’t exercising based on glycemic loads.

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I use the Xtra Precsion as it was the best available 6 years again, More options now.

I listen to the Peter Attia and the Ben Greenfield podcasts occasionally and both of those guys have done or are doing continuous monitoring. Both of them are interested in longevity and, I think, the theory is that minimizing blood sugar spikes leads to better metabolic health. Greenfield used it to identify foods that spiked his blood sugar exceptionally high and then he would eliminate or minimize them. My wife, btw, had gestational diabetes and used a monitor with strips. She definitely find certain foods that spiked her blood sugar more than others.

The fasting community is getting more specific and calling 16:8 or whatever one chooses as a “restrictive eating window”. It’s not really a fast anymore than not eating while you sleep is fasting. In any case, there is no magic to 16 hours. You can start with 12 and then try 13, 14, etc and see how it feels. I like Fung’s ideas but I personally have a hard time integrating them into training.

I do wonder about doing every workout fasted. It seems like that would make you a good fat burner but maybe not as fast as you can be at higher intensities.

I do a lot of this type of testing. I don’t have diabetes and overall my insulin sensitivity and glucose levels are really good (based on my testing).

A couple reasons why everyone should test even if you have nothing wrong.

1: You get a baseline and will be able to identify when something is changing
2: You can find foods that impact you negatively
3: You can identify foods that impact glucose control positively. There are many foods, that if ingested prior to bad foods from #2, will blunt the glucose spike. The order you eat food is very important. There’s a reason you get a salad first at Italian restaurants.

It’s been a while, but I also did testing while riding endurance on trainer. My glucose stayed steady in the 90’s, then at a point it would go to 140 and stay there for a while, then drop. I assumed this was from liver starting to dump glucose. I did some rough calculations based on how many calories I had burned, a rough percentage of how many were from glucose. And that # was close to what I read your legs will store in terms of glycogen. I then tried carb loading and saw this number increase. So I think there is lots to learn.

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