11 Days of Blood Glucose Tracking: What I Learned
“Our cells are at their happiest when the amount of energy they are given matches the amount of energy they need to function.”
―Jessie Inchauspé
For years, I’ve been curious about how my blood glucose levels fluctuate throughout the day—not just during a fasting blood test at the doctor’s office. Understanding how my food, exercise, stress, and sleep influence those levels felt like an opportunity to learn more about my body. So, for two weeks, I strapped on a Continuous Glucose Monitor (CGM) and dove into real-time data. What I expected was validation of what I thought I already knew. What I got was a much deeper understanding of the subtle (and not-so-subtle) ways my choices impact my glucose—and my overall health.
Tracking My Blood Glucose Levels: The Experiment
I used a Freestyle Libre 2 CGM for 11 straight days. (Note: The sensor lasts 14 days but I accidentally caught it on the dryer when I was doing laundry and it deactivated, my only issue with the device the whole time.) This allowed me to track my blood glucose levels continuously without finger pricks. It’s a small sensor applied to the back of the upper arm that syncs with an app, providing real-time feedback and trends. I bring my phone to the sensor and it would give me an immediate reading. I would take a note such as “eating a banana” or “starting a Zone 2 workout” and then see where my blood sugars went over the next 30-90 minutes and even the rest of the day.
My goal wasn’t just to see numbers—it was to identify how meals, exercise, stress, and even sleep influence my glucose and, ultimately, my health. For the first handful of days, I kept my routine the same and for the remainder, I put my body through the wringer: candy, high-intensity workouts, low-intensity ones, full-day fasts, post-prandial walks, high-carb snacks and meals, and no-carb ones. I was aware of many of the responses but totally blown away by others. Here are my notes.
Also, I have no affiliation with Freestyle Libre. I was just able to get a few device that happened to be theirs. :-)
What I Learned
What Had No Impact (No Blood Glucose Spikes)
~21 hour fast.
Fasting: Naturally, not eating anything (coffee excluded) meant my glucose levels were steady with a slight decline throughout the day. This was a ~24-hour fast (dinner to dinner) I do every 1-2 weeks which helps me stay metabolically flexible.
Protein Anything high in protein had little to no effect on my glucose levels. Surprisingly, when I ate a meal that was high in protein with any at least some amount of carbs, such as a turkey wrap, it barely moved the needle.
What Had Some Impact
Complex Carbs: Complex/non-processed carbs such as fruit, veggies, and beans were consistent in causing moderate rises. This was no surprise but it was interesting to see the little differences, such as how banans spikes it noticeably more than an apple, likely because the apple has more fiber.
Waking Up: The dawn effect caused my glucose levels to rise consistently between 4 and 6 AM, even before coffee or food. This natural increase, driven by cortisol and other hormones, set a higher baseline for the morning, which was compounded by coffee. This may explain why I’m such a morning person.
Exercise: Zone 2 training and strength workouts had little impact on my blood glucose, but HIIT sessions consistently caused noticeable increases. This is due to the body’s natural stress response during intense activity, which triggers the release of glucose from the liver and muscles to fuel the effort. Since my workouts typically take place in the morning, when the dawn effect is already elevating glucose, these rises are compounded by the hormonal surge from exercise. Whether I consumed a banana, essential amino acids, or trained fasted, my glucose levels still increased, reflecting the body’s mobilization of energy stores like glycogen to meet the demands of physical activity. Not concerned.
Coffee: My morning black coffee had no carbs or calories, yet it slightly elevated glucose levels. This is likely due to the stimulation of cortisol, a hormone that triggers the release of stored glucose, amplifying the effects of the dawn phenomenon.
Muscle Mass: While I didn’t test this directly, it’s well-understood that greater muscle mass helps absorb glucose more efficiently, reducing post-meal spikes and improving overall glucose control. While my body type is full-on ectomorph, I have some muscle bulk, allowing my body to take a hit from higher carb intakes. This is a far cry from my marathon-running, pasta—devouring days where my sugar levels likely resembled a mountain range.
What Spiked My Blood Glucose Levels the Most
My processed carb experiment day with M&Ms and a Clif Bar.
Rice: Despite eating white rice as part of sushi, it caused high glucose spikes, jacking my glucose up by 40%.
Simple Carbs: One day, in the name of science, I went to town on three slices of pizza and some sweet potato fries. My glucose levels skyrocketed by 26%. Later that day, I tried 2 high-protein (20g) Clif Bar to see if that helped reduce the naturally high carb count (29g) while also going for a 20-minute walk and eating a high-protein meal beforehand (chicken thighs and salad). The spike was still incredibly high (see graph). I was blown away. Not all carbs are created equal when it comes to glucose control.
Candy: Sugar-heavy snacks like M&M’s were the biggest culprits. On one occasion, I ate 25 regular M&M’s in the morning (equivalent to ~ half of a bag), along with a banana, before a workout. My glucose spiked 49% within the hour. Curious about a larger dose, I later tried a full bag (60 M&M’s), which caused a massive 70% increase, peaking at 167 mg/dL—the sharpest spike and highest peak throughout this experiment.
Strategies That Flattened the Curve
Never Start with Carbs: There’s a reason restaurants put bread on your table before meals—it spikes your blood sugar quickly, making you hungrier and more likely to overeat. This is why it’s important to start meals with veggies and greens then move to fat and protein, and end with starches and sugars. Eating fiber, fat, and protein first slows the digestion of carbohydrates, reducing the glucose spike and keeping your blood sugar more stable. While not as much of an impact, eating my carbs naked also spiked my levels more than pairing my carbs with other macros, even if I ate the carbs first.
Movement After Meals: Another simple and effective strategy that was confirmed by my CGM was incorporating movement after meals. A 20-minute walk or light Zone 2 exercise significantly blunted my post-meal glucose spikes. I’ve been doing this work lunchtime routine for years and the numbers show that it’s working: protein, veggies, and fats first then eating my carbs while taking a 20-minute walk (typically a banana or apple).
Better Sleep: Quality sleep also played a critical role. On nights when I logged uninterrupted sleep, my fasting glucose in the morning was lower, and I noticed smaller glucose variations throughout the day. Poor sleep, on the other hand, appeared to amplify the dawn effect.
Berberine: Berberine is a natural compound known for its ability to improve insulin sensitivity and reduce glucose absorption in the gut. My blood glucose spikes after meals were consistently lower, with a green apple causing a 16% increase compared to 24% on a non-berberine day—a 33% reduction. My overall glucose levels were 12% lower that day too. Additionally, glucose returned to baseline faster, typically within 1 hour versus 1.5 to 2 hours without berberine. I took 7,500mg of this kind of berberine.
A scatter plot of my glucose ranges ovr 11 days.
Unique Observations
Sweaty at 69 mg/dL: One evening, my glucose dipped to 69 mg/dL, the lowest over those 11 days, and I found myself sweating and a bit uneasy. The day before I was on an experiment spree and had many swings in my glucose that night before I also went out to dinner and drank beer and some wine, and continued later than I typically would. (That is, on nights i drink, I try to stop ~3 hours before bed.) It was a good eye-opener for how sensitive the body can be long after you fall asleep.
The Dawn Effect: Every morning, my glucose naturally rose around 4-6 AM, even before eating or drinking coffee. This "dawn effect" is caused by cortisol and other hormones preparing the body for the day. While mild in my case, I’ll continue experimenting with timing my first meal or exercise to blunt its effects further.
What I Plan to Do Moving Forward
This experiment gave me a roadmap for optimizing my blood glucose levels—and, by extension, my energy, mood, and long-term health. Moving forward, I plan to focus on balanced meals with plenty of protein, fats, and fiber while minimizing naked carbs. Post-meal walks are even more important now, knowing, and not just assuming that they worked. I plan to make this a family affair.
While 11 days taught me a lot, it was only 11 days, and isolating specific variables to get good enough data takes much more time. I plan to use a CGM again and test it against more variables including vinegar, cinnamon, high carb mornings vs. high carb nights, different types of alcohol, saunan and cold plunges, and longer endurance bouts.
That being said, the insights were invaluable and helped me change and solidify habits for a healthier life.
Key Takeaways
Movement is powerful: Even a short walk after meals made a noticeable difference in flattening glucose spikes.
Sugary snacks create large spikes: Proceed with caution with processed foods like candy and high-carb protein bars.
Timing of meals matters: Protein and fats before starches and sugar make a difference.
No alcohol too close to bed. Avoiding this helps prevent dysregulated sleep and hypoglycemic dips at night.
Related:
