I didn’t eat a single bite of food for 7 days. Just water, electrolytes, and a lot of curiosity. This wasn’t a crash diet - it was an experiment to see what actually happens to the body during a 7-day water fast and how much of the change sticks afterward. I tracked weight, fat loss, lean mass, glucose, ketones, HRV, sleep, and refeeding results with Dexa scans, meters, and wearables.

If you’re wondering what 7 day fast results look like in real life, here’s the full breakdown.

🔥 What Is a 7-Day Fast?

A 7-day fast means going a full 168 hours without food. Just water, electrolytes, and maybe a coffee if you're feeling fancy. Seven days is long enough to fully deplete glycogen, enter deep ketosis, burn meaningful fat, see big shifts in glucose regulation, temporarily lose lean mass (mostly water, glycogen and gut content) and experience real changes in HRV, sleep, and recovery markers.

Basically, it’s long enough to see what the body does when it switches fully into fat-burning mode.

🧠 Why I Did This 7-Day Fast

I’ve done several extended fasts before, including 7-day and 9-day water fasts. Every time, I learn something new about how my body handles stress, recovery, and metabolism.

My goals this time were simple:

burn fat and reset my metabolic flexibility
improve glucose control and insulin sensitivity
measure fat loss vs lean mass loss
see how hydration and electrolytes affect recovery
test mental clarity and productivity
and yes… satisfy my inner health nerd

📊 Starting Metrics Before the 7-Day Fast

Weight: 162.0 lbs / 73.5 kg
Fat mass: 21.4 lbs / 9.7 kg
Lean mass: 133.6 lbs / 60.6 kg
Bone mass: 7.1 lbs / 3.2 kg
Glucose: 92 mg/dL
Ketones: 0.6 mmol/L

📅 Daily Fasting Log

Weight, glucose and ketones during the 7-day fast

📉 7-Day Fast Results: Before and After

Here’s what actually changed after 7 days without food:

Total weight loss: 11.6 lbs / 5.3 kg
- Fat mass: ↓ 4.6 lbs / 2.1 kg (measured by Dexa)
- Lean mass: ↓ 7.1 lbs / 3.2 kg (measured by Dexa)
Bone mass: unchanged
Glucose: dropped from 92 → 68 mg/dL
Ketones: peaked at 6.2 mmol/L (evening of Day 6)

🔍 My Fat Loss Calculations

As an MIT nerd, I even calculated my expected fat loss by dividing the 18,595 calories burned during the week of fasting by 9 (assuming each gram of fat contains 9 calories, and each pound of fat is about 3,500 calories). Result? Spot on: 4.6 lbs / 2.1 kg of fat lost. Pretty cool!

💭 Sleep, Recovery & HRV During the Fast

My sleep and readiness scores (measured by Oura Ring) declined during the fast — no surprise, given the physical stress. Resting heart rate and respiratory rate increased and HRV dropped during the fast, it looks like my body was under a solid stress.

😮 What Surprised Me During the Fast

I lost more lean mass than expected — but a lot of that was likely glycogen and water, not just muscle.
Cravings disappeared by Day 4. I felt in control, not hungry.
By the end, I felt calm, focused, and mentally sharp — almost meditative.
Productivity stayed strong: My work efficiency during the fast was nearly the same as on regular, non-fasting days.

🍽️ Refeed Week: What Came Back After the Fast

I started eating again on Day 8. The first meals were clean: soups, cruciferous veggies, probiotics, and small portions. The refeed week was surprisingly smooth - no bloating, no cramps, no digestive drama. That was a nice surprise!

By the end of the refeed week:

Weight went from 150.5 → 157.2 lbs
Total regain: 6.7 lbs

Weight changes during the 7-day fast and the following 7-day refeed

But here’s the thing: most of that weight isn’t fat.

Fat: went from 16.8 to 17.3 lbs (+0.5 lbs / 0.2 kg)
Lean tissue: went from 126.5 to 132.8 lbs (+6.3 lbs / 2.9 kg)
Bone mass: steady at ~7.0 lbs (DEXA scan noise likely)

Body composition changes during the 7-day fast and the following 7-day refeed

🔬 Metabolic Markers: Back to Normal

Ketones started Day 8 at 4.8 mmol/L but dropped fast:

3.1 → 1.1 → 1.4 →0.8 → 0.6 mmol/L
Why? Carbs and insulin turned ketone production off. Totally normal.

Ketones during the 7-day fast and the following 7-day refeed

Glucose told the same story:

Day 7 ended at 68 mg/dL
Post-refeed peak: 134 mg/dL (thanks, carrot juice...)
Then it gradually dropped to mid-90s

Blood glucose during the 7-day fast and the following 7-day refeed

GKI (Glucose-Ketone Index):

During fast: < 1 (deep ketosis)
After refeed: spiked to 20.9, then stabilized around 15

So yes, ketosis ended quickly, but that’s expected. It’s a flexible metabolic state, not a permanent one.

GKI during the 7-day fast and the following 7-day refeed

💓 Recovery: How Fast Did My Body Bounce Back?

HRV (Heart Rate Variability):

During fast: dropped as low as 18 ms
Post-refeed: bounced back to 50–54 ms

Resting Heart Rate (RHR):

During fast: increased
After refeed: dropped to 43–45 bpm — lower than before the fast

Resting heart rate and HRV during the 7-day fast and the following 7-day refeed

Sleep Score:

During fast: rough, low 60s
After refeed: much better, some nights hit 80+

Respiratory Rate:

Normalized quickly, back to ~12.9/min

🛠️ Tools I Used During the 7-Day Fast

These helped me stay safe, track results, and geek out on the data:

Withings Smart Scale (daily weight tracking)
Keto-Mojo Meter (glucose and ketone tracking)
Oura Ring (sleep and recovery tracking)
DEXA Scan (for accurate body composition - fat, lean, and bone mass)
Ultima Replenisher Electrolyte Powder (electrolytes)
Sherpa Pink Himalayan Salt (just salt 😊)

✍️ Final Takeaways

What Went Well

Digestion stayed smooth
Fat loss was predictable
Metabolic flexibility improved
HRV rebounded fast
Energy after refeed was great

What I’d Do Differently

Start electrolytes earlier
Track how workouts impact energy
Add light strength training sooner to help preserve lean mass

Seven days without food isn’t easy, but it teaches you a lot about stress, discipline, and what your body can handle. Practice makes it much easier.

Would I do another 7-day water fast? Absolutely. Just smarter each time!

📺 Prefer video format? Here’s the link to the full video: Watch on YouTube

7-Day Fast: What Really Happens to Your Body, The Results, and What Came Back After Refeeding