Just Completed My First 3-Day Water Fast - Here's What Happened to My Body

Happy New Year, fellow biohackers! I followed this protocol and just finished my first 72-hour water fast, and figured I'd share the data with you all. Some results were exactly what I would expect from the literature, but there were definitely some interesting surprises!

🧪 The Blood Work Results

Here's what happened to my blood biomarkers after 72 hours of fasting: Fasting Results

TL;DR on blood markers:

Ketones (β-Hydroxybutyrate) went absolutely insane (80x increase!) - deep ketosis confirmed
Insulin dropped 70%
Growth hormone increased 4x
Blood sugar dropped below normal range from 89 to 56 mg/dL (felt fine though)
Free Thyroid hormone T3 decreased 32% (indicative of metabolic slowdown, a biomarker for longevity)

Changes in Urine Ketone levels

Ketone Levels Results

Just for curiosity, I also tracked ketones with urine strips throughout the fast. Here's what I found:

First measurable ketones in urine: 0.5 mmol/L at 22hr
Peak ketone level: 16 mmol/L at 36hr (Day 2, 11:20 PM)
Post-fast ketone persistence: ~58 hours after breaking fast
Ketones returned to undetectable at 130hr (Day 6, 9:00 PM)

Keep in mind that urine strips measure acetoacetate (not β-hydroxybutyrate which is on your blood test) and lag behind blood levels, also accuracy varies by brand. That said, they're cheap and great for tracking trends - strangely mine worked like a binary on/off switch rather than showing a gradual transition into and out of ketosis. And what surprised me the most is that ketones stuck around for ~58 hours AFTER I started eating again!

💚 Changes in Blood Pressure

Blood Pressure Results

My BP is normally on the low side (asymptomatic), but fasting made it drop even more:

Baseline: 100/50 mmHg
Lowest point (Day 4, 12:21 AM): 82/45 mmHg ⚠️
Post-fast recovery (Day 5): Back to 100/65 mmHg Luckily didn't feel any serious symptoms except lacking energy for HIIT or long runs. If you have normal BP, definitely monitor this closely during your fast.

⚖️ Weight Loss & Body Composition

Lost 1kg (2.2 lbs) over the 3 days, noticeably from belly fat. Got some unexpected benefits that I could hold planks longer afterwards, and my body felt more cold-resistant somehow? (might be placebo, idk)

🤔 Interesting Observations

Brain fog during metabolic switching (Day 1 entry & Day 4 exit) made focusing on hard mental tasks difficult, but my mental clarity was good once in ketosis (Days 2). Physical signs included fruity breath from Day 3 (acetone exhaled during ketosis) and increased muscle soreness in my calves by Days 2-3. Despite sauna being generally not advised during fasting (electrolyte loss), personally it helped me a lot with energy and relaxation.

❓ Unanswered Questions & Concerns

Is higher ketone better? Not necessarily. Clinically, blood ketones >5 mmol/L are considered ketoacidosis territory (though mine was 5.63 and I was fine). There seems to be a sweet spot, but I need to experiment on it more.

Lipid panel concerns: Most research shows fasting/keto raises cholesterol, triglycerides, and LDL (didn't test these myself). How bad is this? How to bring it down? Still need to figure this out.

🔄 What I'll Do Differently Next Time

Exit more smoothly: I ate a bowl of noodles too fast and it sent my body into "metabolic panic mode" - resting heart rate spiked just sitting there. Next time I'd do slower and smaller portions.
More light exercise during the fast: add slow jogging or swimming to train my body to utilize ketones better and potentially clear excess blood ketones. Might help with the slightly acidic blood pH I had by hour 72.
Drink high-bicarbonate water: To counter metabolic acidosis (my blood became slightly acidic by the end, indicated by low total CO2).
Try staying in ketosis longer post-fast: I'm curious to transition into low-carb eating after breaking the fast and see how long my body can maintains ketosis.

💬 Final Thoughts

What I gained through the 72hr fast:

Definitely lost weight (mostly belly fat)
Improved glucose metabolism markers
Lowered blood pressure (maybe too much lol)
Learned a TON about my personal metabolism

Started this out of pure curiosity, but now I'm genuinely got interested in ketosis and experimenting with ketogenic diet.

If you are interested in trying out this experiment, you can simply fork the protocol, record your own modifications and share your results. Do your research, talk to your doctor if you have health conditions, and listen to your body. Please keep me posted about your results! And good luck! 😉🍀