My 7-Day Water Fast: The Science, Surprises & My Body Data
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 how my body responds to extended fasting. I tracked everything: weight, fat vs. muscle loss, glucose, ketones, energy levels, and sleep.
And the results? Surprising. Some good, some… well, let’s just say educational.
🧠 Why I Did This Fast
I’ve done several extended fasts before — including both 7- and 9-day water-only fasts — and each time I learn something new about how my body works.
My goals this time were to:
Burn fat and reset my metabolism
Measure the impact on lean tissue and hydration
Improve glucose control and insulin sensitivity
See how fasting affects mental clarity and focus
And of course… satisfy my inner science nerd 😜
📊 Starting Metrics (Day 1)
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 (Morning Measurements)
📉 Final Results After 7 Days
Total weight loss: 11.6 lbs / 5.3 kg
Fat mass: ↓ 4.6 lbs / 2.1 kg
Lean mass: ↓ 7.1 lbs / 3.2 kg
Bone mass: unchanged
Glucose: dropped from 92 → 68 mg/dL
Ketones: peaked at 6.2 mmol/L (evening of Day 6)
🔍 Bonus Insight:
I calculated my expected fat loss by dividing the 18,595 calories burned during the week of fasting by 9 (since each gram of fat contains 9 calories, and each pound of fat = ~3,500 calories).
Result? Spot on: 4.6 lbs / 2.1 kg of fat lost. Pretty cool!
😮 What Surprised Me
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.
✍️ More Personal Takeaways
Practice makes perfect: With every fast, it gets easier to power through the fasting days.
Productivity stayed strong: My work efficiency during the fast was nearly the same as on regular, non-fasting days.
Digestion bounced back fast: That was a nice surprise! I followed all the necessary precautions — small portion sizes, plenty of cruciferous vegetables, probiotic foods, soups, and a gradual refeed.
💭 Sleep, Recovery & HRV Insights
My Oura Ring sleep and readiness scores declined during the fast — no surprise, given the physical stress.
Resting heart rate increased and HRV dropped during the fast, but both bounced back quickly after refeeding.
Respiratory rate also responded: it increased slightly during the fast, but dropped from 13.2 bpm to 12.9 bpm right after, and a month later it's down to 12.4 bpm — a sign of improved parasympathetic tone.
🧂 What I’d Do Differently Next Time
Start electrolytes and salt earlier — especially sodium and magnesium
While I maintained light activity during the fast (walking, stretching), I’d continue tracking how that impacts energy
Plan the refeeding process more carefully — more on that next week
And as always: consult your doctor before trying something like this
🛠️ Tools I Used (Affiliate Links)
These helped me stay safe, track results, and geek out on the data:
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 Thoughts
This 7-day water fast pushed me — physically, mentally, emotionally.
But it also gave me clarity, resilience, and new motivation to keep optimizing.
Would I do it again? Absolutely.
But in a bit smarter way — with better refeed planning and recovery tracking.
👉 Next week’s post: What Came Back After the Fast (And What Didn’t)
