The 72-Hour Fast
Tracker You Deserve
Not another 16:8 app with extended fasting bolted on. Built specifically for 3-day water fasts, with real-time autophagy tracking and expert supplement guidance.
Safety Notice: Extended fasting can affect blood sugar, blood pressure, and electrolyte balance. Consult a healthcare provider before fasting, especially if you have medical conditions, take medications, or have a history of eating disorders.
Everything You Need for a 72-Hour Fast
No fluff. No calorie counting. Just the tools that actually matter for extended water fasting.
Real-Time Phase Tracking
Watch your body transition through 8 distinct phases — from fed state to deep autophagy. Know exactly what's happening at every hour.
Supplement Guidance
Know what's safe to take (magnesium, electrolytes, creatine) and what breaks your fast (collagen, BCAAs). No more guessing.
Autophagy Milestones
Hit 24h, 48h, and 72h markers with visual celebration. See your journey timeline and know what benefits you're unlocking.
Works Offline (PWA)
Install on your phone like a native app. Your timer keeps running even without internet. Data stays on your device.
Refeeding Protocol
Know exactly what to eat when breaking your fast. Avoid the discomfort of eating the wrong foods after 72 hours.
Built by a Faster
Created by someone who actually does 72-hour fasts. Every feature exists because it's genuinely useful, not for marketing.
Why 72 Hours? The Science of Extended Fasting
There's a reason 72 hours is considered the "sweet spot" for extended fasting. Here's what peer-reviewed research tells us:
Peak Autophagy
Autophagy — your body's cellular cleanup process — peaks between 48-72 hours. Damaged proteins and dysfunctional organelles are recycled, promoting cellular renewal.
Research: Ohsumi Y. (Nobel Prize 2016) • Mattson MP, NEJM 2019
Stem Cell Regeneration
A 72-hour fast triggers stem cell regeneration and helps rebuild the immune system. Old, damaged immune cells are cleared out and replaced with fresh ones.
Research: Cheng et al., Cell Stem Cell 2014 (USC)
BDNF & Mental Clarity
Extended fasting increases Brain-Derived Neurotrophic Factor (BDNF), which supports cognitive function and may protect against neurodegenerative diseases.
Research: de Cabo R, Mattson MP. NEJM 2019
Metabolic Flexibility
By 72 hours, your body becomes highly efficient at burning fat for fuel. Growth hormone increases up to 5x, preserving muscle mass while maximizing fat oxidation.
Research: Cahill GF Jr., NEJM 1970 • Ho KY et al., 1988
The 8 Phases of Your 72-Hour Journey
Blood sugar elevated, insulin active, digestion completing.
Insulin drops, growth hormone rises, fat adaptation begins.
Liver glycogen depletes, ketone production starts, mental clarity improves.
Full fat-burning mode, stable energy, hunger fades significantly.
Cellular cleanup activates, HGH peaks at 5x normal, BDNF rises.
Maximum cellular cleanup, senescent cells cleared, mental clarity peaks.
Stem cells activate, immune system regenerates, old immune cells cleared.
Peak benefits achieved, full cellular renewal, ready to refeed.
Peer-Reviewed Research
Our app is built on real science, not bro-science. Here are the landmark studies — summarized in plain English.
Fasting-mimicking diet causes hepatic and blood markers changes indicating reduced biological age and disease risk
Brandhorst S, Levine ME, Wei M, et al. — Nature Communications
In plain English: This 2024 study found that fasting cycles can actually make your body biologically younger. Using blood markers that predict biological age, researchers found that people doing monthly fasting-mimicking diets reduced their biological age by about 2.5 years. Your birthday stays the same, but your body acts younger.
Effects of Intermittent Fasting on Health, Aging, and Disease
de Cabo R, Mattson MP — New England Journal of Medicine
In plain English: This review from the National Institute on Aging (published in one of medicine's top journals) summarizes decades of fasting research. The big takeaway: fasting triggers a 'metabolic switch' from burning sugar to burning fat, and this switch activates powerful cellular repair processes. It's the scientific foundation for why fasting works.
Prolonged Fasting Reduces IGF-1/PKA to Promote Hematopoietic-Stem-Cell-Based Regeneration and Reverse Immunosuppression
Cheng CW, Adams GB, Perin L, et al. — Cell Stem Cell
In plain English: This is THE study that put 72-hour fasting on the map. Researchers found that fasting for 2-3 days flips a 'regenerative switch' — it kills off old, damaged immune cells and triggers stem cells to produce brand new ones. It's like rebooting your immune system. This is why 72 hours became the magic number.
Safety, health improvement and well-being during a 4 to 21-day fasting period in an observational study including 1422 subjects
Wilhelmi de Toledo F, Grundler F, Bergouignan A, et al. — PLOS ONE
In plain English: The largest fasting safety study ever done — 1,422 people fasting for 4-21 days under medical supervision. The results? Fasting was safe, people felt better emotionally and physically, and side effects were minimal. This is the study to cite when someone says 'isn't fasting dangerous?'
We've compiled 10 peer-reviewed studies on fasting — all summarized in plain English.
See All 10 StudiesWhy Not Just Use Zero or Fastic?
Most fasting apps are built for intermittent fasting. Extended fasting is an afterthought.
| Feature | Other Apps | 3-Day Fast |
|---|---|---|
| Built for 72h fasts | Afterthought | ✓ Core focus |
| Detailed phase tracking | Basic | ✓ 8 phases |
| Supplement guidance | None or paywalled | ✓ Free |
| Refeeding protocol | None | ✓ Detailed guide |
| Subscription required | $9.99/mo typical | ✓ Free forever |
| Account required | Yes | ✓ No |
| Works offline | Sometimes | ✓ Always |
Water Fasting Guides
Science-backed articles to help you prepare, fast safely, and get the most out of your 72-hour journey.
Autophagy Guide
When it starts & peaks
72h Benefits
Science-backed reasons
How to Start
Complete beginner guide
Muscle Loss?
NEWThe truth about gains
Refeeding Guide
Break your fast right
Safety Guide
Risks & precautions
Day by Day
What to expect each day
Clean vs Dirty
What breaks your fast
How Often?
Finding your rhythm
Frequently Asked Questions
Everything you need to know about 72-hour water fasting
Is a 72-hour fast safe?
For most healthy adults, a 72-hour water fast is generally safe. However, you should consult with a healthcare provider before attempting extended fasts, especially if you have any medical conditions, take medications, are pregnant or breastfeeding, or have a history of eating disorders.
What can I consume during a 72-hour water fast?
Water (essential), black coffee or plain tea (no sugar/milk), electrolytes (sodium, potassium, magnesium), and some supplements like creatine or B vitamins. Avoid anything with calories, protein, or fat — these will break your fast and stop autophagy.
Will I lose muscle during a 72-hour fast?
Minimal muscle loss occurs during a 72-hour fast. Growth hormone increases significantly (up to 5x) specifically to preserve muscle mass. The body preferentially burns fat for fuel. Most 'weight loss' you see is water and glycogen, which returns when you eat.
How do I break a 72-hour fast safely?
Start with something gentle like bone broth or a small portion of eggs. Avoid large meals, processed foods, sugar, and alcohol for the first 24 hours. Eat slowly and stop at 70% full. Our app includes a detailed refeeding guide.
What's the difference between autophagy at 24h vs 72h?
Autophagy begins around 24 hours but increases significantly between 48-72 hours. At 72 hours, you're experiencing peak autophagy — maximum cellular cleanup, stem cell regeneration, and immune system reset. This is why 72 hours is considered the 'sweet spot' for extended fasting benefits.
Can I exercise during a 72-hour fast?
Light exercise like walking is fine and can even help accelerate ketosis. However, avoid intense workouts, especially in the first 24-48 hours as your body adapts. Listen to your body — if you feel weak or dizzy, rest.
Why do I feel so good on day 2-3?
By day 2-3, your body is efficiently burning ketones for fuel, which many people find provides steady, clear energy without the blood sugar fluctuations. BDNF increases, enhancing mental clarity. Hunger hormones also normalize, so you often feel less hungry than on day 1.
How often can I do a 72-hour fast?
Most people do 72-hour fasts once a month or once per quarter. Some do them more frequently, but it depends on your health status, goals, and how your body responds. More isn't always better — give your body time to benefit from each fast.
Ready to Start Your 72-Hour Fast?
No sign-up required. No payment. Just tap and begin.
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