I’ve done multiple extended fasts before (7 and 9 days), but this was my first full 10-day fast. In this post, I’ll share:

My 10 day water fast results (glucose, ketones, body composition, blood work).
What happens inside the body during 10 days without food.
How a 10 day fast feels - not just the data, but the daily ups and downs.
My plan for fasting going forward.

I know it’s quick a long post, but I hope it’s ok with you and you found it useful 😊

Why I Tried a 10 Day Water Fast

This wasn’t about dropping weight quickly - I don’t have much extra. My goal was to refine my fasting habits, and see how I’d handle one more day beyond my longest 9-day attempt.

I focused on the general health benefits of fasting such as better blood sugar and insulin regulation, autophagy, better metabolic health and others, and on solidifying habits. I picked warm summer days - fasting in the heat turned out to be surprisingly comfortable (except for one brutally stressful day 7, when I learned I’m not superhuman 😊). I tried to keep my daily routine as normal as possible instead of lying around; the goal was to accomplish as much as possible while fasting. And I made fasting background noise rather than the main event, distracting myself with bigger goals so I wasn’t obsessing over food.

What Happens During a 10 Day Water Fast

Here’s what the numbers looked like.

Ketones: Up and Up (Until Refeed)

Started at 0.4 mmol/L → peaked at 8.0 mmol/L by day 10.

👉 A steady climb, with the body running almost fully on fat by the end.

Glucose: A Sharp Dip, Then a Plateau

Started at 100 mg/dL, dipped to the 60–70 mg/dL range, and at some point it even went down to 42 mg/dL. After refeeding, glucose bounced back over 120 before settling closer to baseline.

Body Composition: Fat Loss vs Lean Mass

DEXA scans showed:

Weight: 165.1 → 151.1 lbs (-15.5 lbs / -7.0 kg)
Fat: 23.9 → 18.4 lbs (-5.5 lbs / -2.5 kg)
Lean tissue: 134.1 → 125.8 lbs (-8.3 lbs / -3.8 kg, mostly water/glycogen)
Refeed: lean tissue mostly returned, fat loss remained.

Heart and Breathing Metrics

Resting HR dropped to 41 bpm.
HRV spiked mid-fast, then fell during refeed.
Respiratory rate stayed steady at about 13-13.5/min.

Blood Work and Biomarkers

Improved: inflammation markers (hsCRP), insulin stayed low.
Mixed: sleep quality (deep sleep % was only 7%).
Negative: LDL cholesterol and ApoB went up, white blood cells dropped temporarily.

👉 The body clearly reorganizes its priorities under fasting — some markers improve, others take a temporary hit.

✅ You can find more charts and all fasting data at fasting.center/fasting-results

How It Feels to Do a 10 Day Fast

The data is clean, but the daily reality is a little messier.

Preparation (Days -2 and -1)

Day -2 (Saturday): Hosted a BBQ with friends. I intentionally overate to “build hate” toward food. Odd strategy, but it worked surprisingly well.
Day -1 (Sunday): Played soccer and kept meals light.

Early Days (1–3): Excitement and Transition

Day 1 (Monday): Slept great - I was super excited to start. Coffee with heavy cream at 7 am, and the fast officially began. Did a DEXA scan right after (always a motivator). It also happened to be my 18th wedding anniversary. My wife wasn’t thrilled about celebrating with just water 😊, but love is compromise ❤️. To speed up ketosis, I went all-in at the gym: cycling, running, steam room - burned about 720 calories. Staples: Ultima electrolytes (2-3 packets/day), hot water with pink salt, San Pellegrino.
Day 2 (Tuesday): First calf cramps, fixed with electrolytes. Gym: cycling, strength training, steam room. Kept reminding myself this wasn’t about “surviving” - it was about using 10 days to get stuff done.
Day 3 (Wednesday): Slept unbelievably deep - so deep it was hard to wake up. Probably from cutting coffee (black coffee is not my thing). Realized fasting in summer is nicer than in winter, even in California. Gym: cycling, running, steam room. Eyes started feeling tired, vision slightly off.

Middle Stretch (4–7): The Grind

Day 4 (Thursday): More calf cramps. Gym: cycling, strength training, steam room. First tiny bowel movement since starting the fast.
Day 5 (Friday): Resting heart rate dropped to 41. My all-time low was 38, but that was 10 years ago. Big realization: poor sleep during past fasts wasn’t from physical stress but from mental stress about fasting itself. This time, feeling relaxed made fasting much easier. Gym: cycling, running, steam room.
Day 6 (Saturday): Night HR: 42, another solid night. No workouts - instead, a full day at my son’s soccer tournament in 95°F heat. Brutal. Eyes irritated, felt drained all day.
Day 7 (Sunday): Morning cramps again, electrolytes fixed them. The hardest day. Another soccer tournament in 95°F heat. Glucose dropped to 41 (quickly rebounded to 60). Ketones hit 7.4, my all-time high. To add stress, I read a Reddit post about someone ending up in the ER with gallbladder issues. Exactly what I didn’t need. Eyes still irritated. Pool time with my family saved the day - cooling down helped a lot. This was the day I confirmed I’m not superhuman 😊. Who knew?

Final Days (8–10): Low Energy, High Ketones

Day 8 (Monday): Morning cramps again, electrolytes helped but not fully. Eyes still itchy, eye drops gave relief. Gym: cycling, short run. Energy definitely lower. Another tiny bowel movement. Ultima electrolytes became disgusting - every flavor.
Day 9 (Tuesday): Morning cramps again, electrolytes less effective. Took it easy. Morning ketones at 7.9.
Day 10 (Wednesday): Same cramps. Gym: cycling, short run, steam room.

Refeed (Days 1–5)

Day 1 (Thursday): Morning cramps again. Did a DEXA scan, full blood panel, and epigenetic clock. Broke the fast with boiled broccoli and bone broth. Wild post-fast party food. Felt odd at first to eat again, but it passed quickly. Later: coffee with heavy cream (finally), more broccoli, Brussels sprouts, and cheese. Felt amazing.
Day 2 (Friday): Cramps still around. First real bowel movement — volume, timing, everything felt normal. Eyes improved. Eating almost normally but chewing carefully.
Day 3 (Saturday): Eating close to normal. In the evening, went to a party (classic Eastern European potluck where everyone brings enough food for 20). Sampled everything, even a little beer. Felt great.
Day 4 (Sunday): Back to regular food. Zero sugar cravings — a big win. First light strength workout post-fast to avoid injury.
Day 5 (Monday): Regular cardio: cycling, running, steam room. Officially done with “careful monitoring.” Back to normal eating and training.

Summary of the Experience

Easier than past fasts - mentally and physically.
Smoothest refeed yet.
Lost 15.5 lbs total (5.5 lbs fat).
Biggest challenge: heat + family logistics.
Biggest surprise: fasting became background noise once I stopped stressing about it.

10 Day Fast Results at a Glance

Weight: -15.5 lbs.
Fat loss: -5.5 lbs.
Ketones: 0.4 → 8.0 mmol/L.
Glucose: 100 → stable at 65–70, though one hour it went down to 42
Resting HR: 41 bpm.
Biggest win: mental clarity and a smooth refeed.

FAQs About a 10 Day Fast

Q: How much weight can you lose on a 10 day water fast?
Usually 10-20 lbs. For me, it was 15.5 lbs, with 5.5 lbs of that being fat.

Q: Is a 10 day fast safe?
It depends. With prep and electrolytes, it can be fine for healthy people. But it’s not for everyone - medical supervision is smart.

Q: What should you eat after a 10 day fast?
Start small: broth, steamed veggies, chew slowly. Add protein and fat gradually.

Q: Do you lose muscle on a 10 day fast?
Some lean tissue goes down, but most is water and glycogen. Mine came back within 12 days of refeeding.

Takeaways

A 10 day water fast is not mystical or magical. The body simply shifts gears: burns fat, conserves energy, reshuffles biomarkers.

The experience confirmed a few things for me:

Fat loss is measurable.
Lean mass rebounds.
Day 7 is a reminder I am a human, not a superhuman 😊
Fasting works best when you stop making it the center of your life.

My plan: one extended fast per year, shorter fasts more regularly, and a new focus on building muscle.

10 Day Water Fast Results: Data, Experience, and Takeaways