Since I started self-experimenting to better manage my diabetes, one of the things I was most interested in was the effect of different foods on blood sugar. I follow a low-carb/keto diet and I was particularly interested in confirming if low-carb flour and sugar replacements (e.g. oat-fiber, inulin, allulose, etc.) really have as little impact as claimed.
When I first tried this, I added ingredients to my normal meals measured the change in my normal BG trends. This proved too noisy and I couldn't get a clean measure of the effect of even pure glucose in a reasonable number of measurements (design, results).
For these experiments, I isolated the effect of the ingredient being tested by fasting for 17 h before eating/drinking. This worked really well and I was able to get reliable measurements and some (hopefully) interesting insights.
I hope some people find this interesting. If you have any questions, comments, or suggestions for future experiments, I'd love to know.
Lastly, if you're interested in joining in any future experiments, let me know in the comments or send a via the contact form or to quantifieddiabetes_at_gmail.com.
- Design experiments and solicit feedback: blog, Reddit, OpenHumans
- Establish fasting baseline & determine time of day for experiments
- Food effect measurements:
Results for ingredients without links are in this post.
- The main macronutrients, carbohydrates, protein, and fat have the expected impact. Notably:
- Contrary to some claims I've read, fat had virtually zero impact on my blood sugar.
- Starch and glucose had nearly the same impact, though slightly delayed in time. This suggests that for purposes of carbohydrate counting, I can treat all digestible carbohydrates the same.
- Insoluble or "indigestible" fiber had a wide range of impact, from near zero for oat fiber, ~10% of glucose for inulin, to 76% of glucose for resistant wheat starch.
- This is extremely disconcerting, as both oat fiber (iAUC 0.4% of glucose) and resistant wheat starch (iAUC 75% of glucose) are listed as insoluble fiber on nutrition labels, but have radically different impact on blood sugar. Given the lack of clarity and quantification of ingredient lists, this makes it nearly impossible to predict the blood glucose impact of a food without eating it and testing.
- My two preferred non-nutritive sweeteners, allulose and erythritol had negligible impact on my blood glucose.
- Adding oat fiber to glucose had a negligible impact on blood glucose, though the time to peak was increased by 30 min. Further testing with different types of fiber and other macronutrients would be required to get a better handle on this effect, but the initial results suggest that while fiber might have an impact on rate of glucose absorption, it's not signifiant enough to change the blood glucose impact for insulin-dependent diabetics (might be very different for someone who makes more endogenous insulin).
Measurements. Blood glucose was measured using a FreeStyle Freedom Lite glucose meter with FreeStyle lancets & test strips. No special precautions were taken to clean the lancing site before measurement. To take a sample, the lancing devices was used to pierce the skin at an ~45° angle from the finger. Blood was then squeezed out by running the thumb and pointer finger of the opposite hand from the first knuckle to the lancing site of the finger. Blood was then wicked into a test strip that had been inserted into the meter and the glucose reading was recorded.
Data Processing & Visualization. iAUC was calculated using the trapezoid method (see data spreadsheet for details). Data was visualized using Tableau.
Medication. I took my normal morning and evening medication, but did not dose for the experimental food ingested.
- Fat had virtually zero impact on my blood sugar. I've read a lot of posts and comments by people who dose a small amount of insulin based on the fat content of a meal. The claim is that it does increase their blood glucose, though much less than carbohydrates or proteins. My (limited) measurements do not show this.
- If anyone reading this does see blood glucose rise with fat intake and is interested in doing a joint experiment to measure it, please let me know in the comments or send a PM via the contact form or to quantifieddiabetes_at_gmail.com.
- Cornstarch had virtually the same impact on as glucose, just slightly delayed in time. Given the difference in their glycemic index (100 vs. 70), I would have expected a larger effect. That said, this suggests that for purposes of carbohydrate counting, I can treat all digestible carbohydrates the same.
Key results in the Summary section above.
Overall, the experiment was successful, yielding a reliable measure of the impact of the major macronutrients and my most commonly used low-carb ingredients. I also got preliminary insight into the interaction effect between glucose and insoluble fiber.
Due to external circumstances, I didn't get to as many ingredients as I'd have liked. I may come back and do further experiments. I'm particularly interested in testing a wider range of purportedly low-carb ingredients and diving deeper into interaction effects (maybe looking foods with a range of different carbohydrate:protein:fat:fiber).
That said, these experiments were very time consuming and the frequent extended fasts were disruptive to my normal routine. I need to either find a simpler/easier experimental protocol or get more people to join in to accelerate data collection.
In the meantime, my plan for next experiments is:
- Re-tune basal and bolus (meal) insulin doses
- My routine has changed a lot due to working from home, changing doctors, and changing medication (due to insurance requirements). Plus, I was able to get a Dexcom G6 CGM, which is showing accuracy comparable to my blood glucose meter. Blood sugars are still good, but I think I can get them better.
- Re-measure blood sugar impact of glucose and insulin; compare to previous data
- While working from home, I've gained some weight (and hopefully muscle). This has resulted in a change in my insulin sensitivity. Not huge, but I need to remeasure to have an accurate baseline for future experiments.
- Test the effect of some dietary supplements that have been reported to affect blood sugar in the literature, but where data insufficient or contradictory
- Vitamin C (reported to cause blood glucose meters to read higher than actual, but all measurements I can find are for injected vitamin C)
- Glutamate (reported to reduce post-prandial glucose, but magnitude and timing vary widely)
- Others tbd.
As always, if you have any questions, comments, suggestions, or are interested in joining in future experiments, please let me know in the comments or send a PM via the contact form or to quantifieddiabetes_at_gmail.com.