48 hours of Blood Sugar Tracking

Tl;dr (full details here): I have Type 2 diabetes and spent 2 days last week testing my blood sugar every 15 min. I learned a ton that I didn’t know from my normal testing regimen, including that I was hypoglycemic more often and more severely than I realized.

I posted the methods, all data, and my analysis here.

Details & Questions:

Normally, I only check my blood sugar at key times (waking, going to bed, before injecting insulin, before eating, and 1 & 2h after eating). To see if there was anything to be learned from what’s happening the rest of the time, I decided to spend 2 days checking my blood sugar every 15 minutes.

Since I have Type 2 diabetes, my insurance won’t cover a continuous glucose monitor (CGM). Plus, blood glucose meters (BGM) are more accurate, even according to CGM manufacturers. So, for this experiment, I used my Freestyle Freedom Lite and just measured by blood glucose every 15 minutes.

This ended up being way more useful than I expected. There was a lot more going on between the times I usually measure than I realized. Here’s a most important things I learned, my new questions, and ideas for next experiments:

Key Learnings:

  • Shorter testing intervals around key times is extremely informative. My normal routine of testing blood sugar before and 1 & 2h post-meals is not sufficient. There’s a lot going happening on both shorter and longer time-scales that will be useful for understanding the effects of different interventions and for optimizing medication.
  • I’m spending far more hypoglycemic than I had realized, most notably when I exercise.
  • My peaks in blood sugar from breakfast and lunch occur >3h post-meal and persist until my next insulin dose. This is way longer than I expected and indicates that I need to switch to a longer acting insulin or change something about the meals.
  • My blood sugar drops significantly during cardio exercise (MMA, biking), then returns to normal over 30-45 min. I need to find a way to mitigate this to prevent my blood sugar from going dangerously low.


  • What is happening to my blood sugar between waking and breakfast? Any risk of hypoglycemia while driving to work?
  • Is the long-duration peak in blood sugar after breakfast and lunch real & consistent? If so, what causes it and can it either be shortened by modifying the meal or mitigated using a longer-acting insulin?
  • What is the effect of different types of exercise? How can I mitigate or offset the initial drop in blood sugar during cardio without causing high blood sugar after the recovery?
  • What is the effect of dinner, disentangled from exercise?

Next Experiments:
I’m always interested in ideas for new experiments, so please leave a comment if there’s something you’d like me to try.

  • Exercise studies: Measure blood glucose at 15 min. intervals for different duration and intensity bike rides and weight lifting. Also try varying time since last insulin dose and food eaten before exercising.
  • Long peak from breakfast & lunch: Measure blood glucose at 15 min. intervals a few more times after breakfast & lunch. Try varying protein and fiber content to see if those are the causes. Try normal-acting insulin to mitigate.
  • Food & medication studies: It’s proving difficult to disentangle the numerous effects going on at any given meal by adding or subtracting particular foods (data too noisy, too many measurements required to observe a statistically significant effect). Instead:
    • Skip meals and medication to measure background trends.
    • Consume individual ingredients (glucose, protein, fiber, etc.) or take individual medications to measure their direct effects.
    • Measure combinations of ingredients and medications to measure interaction effects.
    • This will require more experiments, but I think in the end it will require less time & effort to get reliable results.


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Measured blood glucose concentration vs. time from 4a-12p, with annotations for key events. Reference bands and lines show target range and high/low thresholds.


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Measured blood glucose concentration vs. time from 10a-5p, with annotations for key events. Reference bands and lines show target range and high/low thresholds.


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Measured blood glucose concentration vs. time from 4-11p, with annotations for key events. Reference bands and lines show target range and high/low thresholds.


Thanks for sharing!

If you are going to do more experiments, I’d reconsider trying a CGM:

  • CGM manufacturers advise doing fingerstick measurements prior to “treatment decisions” because blood sugar in the interstitial fluid lags, so instant readings have to be extrapolated, and can be way off. But this has no bearing on the data you look at later.
  • Depending on where you live, cost shouldn’t be an issue for a limited-duration experiment: I paid ~USD40 out-of-pocket for a 2-week FreeStyle Libre sensor.
  • That said, these sensors don’t seem to work for some people (about 1 in 5, based on annecdotal evidence), plus I don’t know if the sensors are MMA-compatible :slight_smile:

Even as a non-diabetic, I’ve noticed occasional long-duration peaks, e.g. after eating a large portion of french fries (still not entirely sure why), or after eating very late (which is somewhat expected).

I suspect a reductionist approach doesn’t work here, i.e. effect of a meal doesn’t equal the sum of its ingredients, but you can try known interventions, and see if they have an effect or not…

When your blood sugar drops during exercise, do you feel any symptoms?

I’d love to try out a libre. I had been using one a few years back (bought on ebay) and found it extremely useful, though significantly less accurate than my normal meter. It’s not just a lag due to interstitial fluid, it would often show readings that were much higher or lower than the finger stick meter for long periods of time. That was the old version, though, and I’ve heard the new one is more accurate.

When I went to try to get a libre for this experiment, though, I couldn’t find them on ebay or anywhere else without a requirement for a prescription. I posted this experiment in r/diabetes on Reddit and someone offered to buy and send me one from Canada. I’m going to take them up on it and see if they’re accurate enough for me to use.

On your other points:

  1. I’ve also consistently seen long duration peaks with large meals or when eating late. According to my endocrinologist, this is a well-known phenomenon where your digestion slows with big meals or when eating late at night. In this dataset, though, the meals were only 400 kcal and early in the day, so I don’t think that’s it.

  2. Definitely agree that there’s likely interaction effects between the different ingredients. That’s conventional wisdom among diabetics (e.g. fiber slowing blood sugar rise), but I haven’t seen any studies looking at it under circumstances where there weren’t confounding effects (poor measurement quality, ability of participants to change total quantity of food eaten, etc.). I plan to test this over the next few weeks, first measuring the effect of individual macronutrients (protein, sugar, fat), then measuring combinations to test for interaction effects. I’ll report how it goes once I have the data.

  3. Regarding symptoms of low blood sugar during exercise. My normal symptoms of low blood sugar are heart racing, sweating, and shaking, all of which are unfortunately also symptoms of exercising. The only sign I have is that I sometimes get irritable when my blood sugar is low. I’ve observed myself as more irritable than normal a few times while exercising, but it’s so subjective I’m not confident in my observation.

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Spoke too soon about the lack of studies about interaction effects. Was going through my queue of papers to read and found one one macronutrient order. Limited data, but shows a pretty dramatic reduction in glucose rise when eating meat and vegetables before carbs instead of the reverse. The total carbs were way higher than anything I’d eat, but still indicates this is worth looking at it detail.

Insurance won’t cover it, but surely your endocrinologist (or regular doctor) would write you a prescription?

I’m going to try at my next appt. in 2 weeks. My endocrinologist is great, but he doesn’t think flash CGMs are accurate enough to use for treatment. I’ll need to convince him I’m still going use the regular BGM for treatment and just augment with the CGM. Should work…

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Really interesting project, thank you for posting this and including the graphs. How much food tracking are you doing? (Detailed food tracking is a hassle, I know from experience, but since you did finger prick tests every 15 minutes you clearly have good tolerance for hassles!)

I don’t track my food, but I do keep it consistent.

Breakfast and lunch are 1 serving Ketochow with 2 tbsp. butter and 3 oat-fiber protein muffins (406 calories, 44 g protein, 5.7 g net carb.).

Dinner (if eating in) is 300 g meat and 150 g low-carb vegetable (spinach, okra, broccoli, cauliflower, green beans). Since I change up the meat and vegetable, this is the most variable, but based on my blood sugar numbers, it doesn’t make too much of a difference. When I first started really aggressive blood sugar control, I tried to keep dinner consistent as well, but it drove me nuts.

BTW, a comment on my reddit post to the Quantified Self subreddit suggested you were the person to talk to about participating in a QS Show & Tell. I’d love to do that after I collect a bit more data and nail down a few more of my big questions.

Do you know how I sign up for that?

Hi Steven, Where are you located? (You can email me at gary@quantifiedself.com and we can discuss.)

I live in the Bay Area, but travel isn’t necessarily a problem, as I have to do so often for work. Sent you an e-mail.

I did another day of tracking, this time while fasting. Here’s the details if anyone’s interested.

Tl;dr (full details here): I saw a weird drop in blood sugar while trying to quantify the effect of eating glucose. To better understand my baseline blood sugar variations, I monitored every 15-30 min. while fasting (still working on getting a Libre). I saw several interesting phenomena that I hadn’t picked up on from my previous all-day monitoring and now have a lot more to investigate.

I posted the methods, all data, and my analysis here.

I’m always interested in ideas for new experiments, so please leave a comment if there’s something you’d like me to try.

Details & Questions:

I tried this week to measure the effect of different food ingredients on my blood sugar. I started with plain glucose, but quickly ran into a problem. The first two times I ate 3g of glucose, which normally would raise my blood sugar ~15 mg/dL, my blood sugar actually dropped. I did these experiments at 2pm, 8.5 h after eat breakfast, so I shouldn’t have had any effects from either the food or medication.

Based on these results, I’m not going to be able to get clean measurements of the effect of food unless I better understand my baseline blood glucose, so I decided to monitor my blood sugar during a day of fasting.

As with my two-day tracking experiment a couple weeks ago, this was quite informative. Here’s a most important things I learned and some questions for the group:

Key Learnings (full data and summary statistics here. I can’t figure out how to put the images into this reply.):

  • Checking blood sugar during a fast is a useful control experiment and helps determine if the phenomena I’m observing are due to specific interventions vs. natural or time of day-based variation.

  • Even with my morning insulin, I’m seeing an ~10 mg/dL increase that persists for ~5 h. I should try increasing the dose by ~0.25u.

  • There’s a measurable drop in my BG when I’m driving to/from work. I saw this in 3/4 of the drives during my previous glucose tracking experiment, but I didn’t pick up on it because my commutes occur right before mealtimes. Need to investigate further to see if this is real & consistent.

  • I saw an ~15 mg/dL drop starting at 1p that persisted until 5:30p.

    • This is the time period when I was trying to do the food effect tests and may be why I was seeing the weird drop in BG.

    • This occurred 9 hours after my last dose of insulin (0.5u each of Novolog and Tresiba), so must be the result of something my body is doing. Is this drop from fasting (e.g. running out of glycogen) or something that occurs normally?

    • My BG stabilized at 65-75 mg/dL, which indicates that that range is something that can occur naturally and not due to medication. Given this, should I correct lows in this range or let them be?

    • I always get tired around 2-3p, lasting until about 5-6p. I’ve always chalked this up to the end of the work day and then getting re-energized by dinner/being home, but maybe there’s more going on. Need to test interventions to eliminate this afternoon fatigue.


  • How consistent are the effects I observed? Which are due to fasting vs. effects that occur during a normal day?

  • Is the driving effect real? If so, are there ways to mitigate it? Even if it’s only a short-term effect, it could be causing fatigue or other reduced mental capacity while driving.

  • How can I mitigate the 10 mg/dL increase in the morning?

  • Is the afternoon drop connected with feeling tired and less mentally capable? If so, how can I mitigate the effect?

Next Experiments:
I’m always interested in ideas for new experiments, so please leave a comment if there’s something you’d like me to try.

  • Repeat this fasting experiment a couple more times to see if the observations are reproducible.

    • Also try fasting for shorter durations (single meals) to check if effects are from the duration of the fast vs. ones that would occur normally.
  • Measure fatigue and/or mental acuity see how it correlates with time of day and BG.

  • Test an increase in morning insulin to reduce the effect of the dawn phenomenon.

If you’ve made it this far and are interested in the full details, I posted the methods, all data, and my analysis here.

Also, I’m always interested in ideas for new experiments, so please leave a comment if there’s something you’d like me to try.

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Interesting observation… I haven’t found driving to affect my blood sugar directly, but blood sugar responses to snacks or meals are often worse than expected, especially when driving on unfamiliar roads in the dark, or in the presence of too many other drivers with “reduced mental capacity” :wink:

I am curious on how you imported the freestyle data. I have it in a CSV but cannot find way to get it into EventLoggers.

For the Freestyle Lite (not the continuous meter), I wrote my own logging app using Pythonista. I record the data in that, which is then saved in an excel file in my Dropbox.

For the Freestyle Libre (continuous meter, just got one), I export the data to csv using Abbot’s software, then process the data using a python script. I’ll be writing up my first post on this in the next week or two and will include the code.