How Extended Fasting Improved My Blood Sugar Regulation

Hey folks! I wanted to share how extended fasting has changed my blood sugar regulation. As you might know, blood sugar regulation - along with lower inflammation, improved metabolic health, and better heart function - are among the most science-documented benefits of fasting.

So, I’ve been tracking my blood sugar closely since I tend to get pretty big spikes after meals. And as you might know, I’m a huge fan of fasting, so I wanted to find out if extended fasting could actually improve blood sugar regulation and flatten those post-meal glucose spikes.

To test this, I measured how my glucose responded to the same foods before my 7-day fast in November 2024, then right after, and four months after my second extended 9-day fast in February 2025.

I used a Dexcom G7 continuous glucose monitor to capture real-time data. Here’s what I found.

My Results: Fasting and Blood Sugar Spikes

🍚 White Rice (100g, 360 cal)

• Pre-fast (Mar 2024): 274 mg/dL

• 1 month post-fast (Mar 2025): 200 mg/dL

• 5 months later (Jul 2025): 207 mg/dL

Blood sugar spikes from 100 grams of dry white rice

🍁 Maple Syrup (37g, 100 cal)

• Pre-fast (May 2024): 233 mg/dL

• 1 month post-fast (Mar 2025): 118 mg/dL

• 5 months later (Jul 2025): 163 mg/dL

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Blood sugar spikes from 100 calories of maple syrup

🍌 Bananas (2 medium)

• Pre-fast (Dec 2023): 242 mg/dL

• Right after fast (Feb 2025): 118 mg/dL

• 5 months later (Jul 2025): 187 mg/dL

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Blood sugar spikes from 2 bananas

Right after fasting, my post-meal glucose peaks dropped dramatically — in some cases by more than half. Five months later, the spikes crept up again but still stayed much lower than before the fast.

That aligns perfectly with what research shows: fasting improves blood sugar regulation and insulin sensitivity for weeks to months, although some of the benefits fade unless you keep your metabolism challenged with clean nutrition, workouts, and periodic fasting.

How Fasting Boosted My Insulin Sensitivity

To see what was actually happening inside my body, I measured glucose and insulin levels before and during my 9-day and 10-day fasts, and after refeeding. I then calculated HOMA-IR, a standard marker of insulin resistance.

Lower HOMA-IR = better insulin sensitivity and more stable blood sugar regulation.

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HOMA-IR before and during extended fasts

During the fast, my insulin sensitivity more than doubled — HOMA-IR dropped from 0.67 to 0.23. That means my body needed three times less insulin to keep glucose stable. That’s exactly what fasting physiology predicts: when insulin stays low for several days, the body resets its sensitivity, clears out old cell components through autophagy, and switches to burning fat and ketones as the main energy source.

I’ll retest the same foods four months after my recent 10-day fast to see how long this improvement in blood sugar regulation lasts.

You can see all my insulin, blood sugar, and other fasting data and charts on the Fasting Results and Data page.

Science Behind Fasting and Blood Sugar Regulation

Here’s what research shows about why fasting helps regulate blood sugar and reduce insulin resistance:

1. Lower Insulin and Glucose Levels: After about 48 hours of fasting, insulin drops sharply and glucose stabilizes. This “rest period” helps retrain insulin receptors and improves how cells respond when food returns.

2. Improved Mitochondrial Function: Fasting triggers autophagy — your body’s cleanup process that removes damaged mitochondria and other cellular junk. That boosts metabolic efficiency and glucose regulation.

3. Reduced Liver Fat: Studies show fasting reduces hepatic fat, one of the major drivers of insulin resistance. Less liver fat means smoother glucose control and healthier fasting glucose levels.

4. Enhanced Muscle Glucose Uptake: Once insulin sensitivity improves, muscles absorb glucose faster after meals, which prevents large glucose spikes and keeps energy levels more stable.

If you’re curious about the broader science, check out my Fasting Benefits page — where “Improves Blood Sugar & Insulin Regulation” is listed as benefit #2.

How Long the Effect of Fasting Lasts

From both my own data and what the literature shows, the improvements in blood sugar regulation from extended fasting usually last 3-4 months, depending on

• diet quality and carb intake,

• physical activity (especially strength training), and

• whether you continue intermittent fasting afterward.

By month 5, some of the benefits fade, but my blood sugar peaks are still far below where they were a year ago. That’s what I call a real metabolic upgrade.

Final Thoughts on Fasting and Blood Sugar Regulation

Extended fasting isn’t for everyone. It’s challenging, and it should be done carefully — ideally with a plan and medical guidance if you have any health conditions. But for me, fasting has been one of the most powerful ways to reset insulin sensitivity, flatten glucose spikes, and stabilize daily energy. For context, my A1c is 5.3%, which means I was already metabolically healthy. Still, the improvement after fasting was obvious — both in the data and in how I felt.

If you’ve noticed changes in your blood sugar after fasting, share your experience — I’d love to see how your numbers compare. Real-world data makes fasting science a lot more fun!