The evidence-led UK guide to 3–10 day water fasts: a day-by-day protocol, electrolyte targets worked out for your weight, a refeeding plan, and who should not fast. Free. Not a quick fix. Not a diet. A complete metabolic protocol.
Should you fast? Two-minute check → The founder’s story → People fasting right now →
Four steps, in the order they matter. Each one is free.
Questions as they come up? The AI coach (the chat button) answers from these pages at any hour. Mid-fast? See where others are.
No calorie counting. No meal prep. No points system. No shakes. No compromises.
For 7 days, you eat NOTHING.
Not "very little." Not "500 calories." Not "meal replacement bars."
NOTHING. ZERO. NADA.
This protocol isn't for everyone. It requires mental fortitude most people don't have. It requires facing yourself when the dopamine is gone, when comfort is unavailable, when discipline is all you have left.
Can you do it?
More importantly: should you?
Medical screening required. Not suitable for everyone. View contraindications
Ten years of peak fitness. Two years of decline. Seven days that changed everything.
Ten years ago, the gym wasn't a chore—it was a sanctuary. 5K runs felt effortless. I could feel my heart pumping, my muscles working, my mind clearing. I was alive.
Then life happened. Not dramatically. Slowly. Insidiously.
A demanding job. Long hours hunched over a desk. The gym visits became sporadic, then rare, then non-existent. The runs stopped altogether. I told myself I'd get back to it. Next week. Next month. After this project.
Two years passed. Ten kilograms appeared—quietly, almost apologetically, around my waist. My clothes didn't fit. My energy crashed. My health app, in its algorithmic indifference, flashed two words that broke me:
HIGH BMI
For someone who'd always identified as fit, as strong, as disciplined—those two words were devastating.
I could've spiraled. Made excuses. Blamed age, stress, genetics. But that Saturday, buried in work, I accidentally stumbled onto something powerful: I forgot to eat. Not intentionally. I just... lost track of time.
By evening, I was hungry. But instead of breaking and gorging (my usual response to missing meals), a thought struck me:
What if I just kept going?
Not as a diet. Not to lose weight. As a test. Could I still do hard things? Was I still that person who chased impossible goals?
Day 2: The headache hit like a hammer. Not "uncomfortable"—crushing. My body screamed for food. Every commercial, every smell, every thought was torture. People describe fasting as feeling "lightheaded." Let me tell you: there was nothing "light" about it.
Day 3: This is where protocols fail. Not from physical inability, but because everything piles up at once: real hunger, a broken routine and the loss of the one reward you could count on every day. It felt like psychological warfare.
I survived on black coffee and sheer bloody-mindedness. I turned it into a personal battle. I needed to prove to myself that I was still the man I used to be—a man who chases goals regardless of obstacles.
Day 5: Suddenly, inexplicably, I felt clear. Sharp. Focused. My body had made the switch—from glucose to ketones, from external to internal fuel. I was running on myself.
I supplemented with multivitamins to support enzymatic function and walked every day. I like to think my body wasn't just losing weight but renewing itself: fasting is known to switch on the cell's recycling system, autophagy, in animals, though no test could have told me how much it was happening in me. Growth hormone was helping my muscles hold on to protein. What I could feel was the clarity, and it felt almost pharmaceutical.
But more importantly than the numbers, I'd proven something: I still had it. The discipline. The grit. The refusal to quit when it hurt.
Breaking the fast required more discipline than the fast itself. When food returns, insulin rises and pulls phosphate, potassium and magnesium into cells; in someone at risk, a big load of carbohydrate can tip that into refeeding syndrome. I didn't gorge. This is what I ate:
Then straight into strict ketogenic eating (our Keto Protocol), which made the following weeks easier for me; it does not guarantee the weight stays off. Our menu today starts with dilute bone broth rather than avocado: see the refeeding guide.
Critics said I'd gain it all back immediately. They were wrong.
I stayed in nutritional ketosis. Little water weight came back, and the mental clarity stayed with me. That was my experience; yours may be different. The discipline became a habit.
This isn't a diet. It's a metabolic reset that integrates with a complete wellness system:
I feel clearer, lighter, stronger. And I'm already looking at the calendar, wondering: Could I do 10 days next time?
Use the Metabolic Calculator to determine realistic timelines based on your individual physiology. Get personalised supplement recommendations and a customized protocol.
Calculate My ProtocolKnowing what your body is doing makes the hard days easier to read and less likely to end your fast early. This is what happens, stage by stage, with the numbers human studies have measured and the places where the timing in people is still unknown.
Primary Fuel: Glucose from your last meal, then from liver glycogen, burned alongside fat
Hormones: Insulin declining, glucagon rising
Cellular Activity: Autophagy, the cell's recycling system, ticking over as part of everyday maintenance
Hunger usually mild, rising around your normal mealtimes: real hunger signals and habit together. Energy usually normal.
Primary Fuel: Liver glycogen (glucose reserves ~100-120g) and newly made glucose (gluconeogenesis), which in one study already supplied about half of glucose production after 14 hours, while fat use climbs
Hormones: Insulin falls; glucagon and growth hormone responses vary between people
Cellular Activity: Ketones, low at the start, begin to rise. When autophagy picks up in people is not known
Hunger often rises around your usual mealtimes. Mental function normal. First signs of metabolic shift.
Primary Fuel: Fat, increasingly as ketones. Liver glycogen is largely spent by hour 24 to 36; in one study, newly made glucose supplied over 90% of glucose production by hour 42. By about Day 3, fat supplies most of the energy you burn
Hormones: Insulin keeps falling; cortisol, noradrenaline and growth hormone often rise, by amounts that vary between people and studies
Cellular Activity: Blood ketones rising, at levels that vary widely between people
⚠️ This is the danger zone: Headaches (salt and fluid loss can contribute), strong hunger, irritability, fatigue, brain fog. A sudden, severe headache is not part of this: call 999. This is a common point to stop.
Primary Fuel: Free fatty acids and ketones. After about three and a half days, ketones supplied roughly a quarter of the brain's energy in one study; they become its main fuel only after weeks
Hormones: growth hormone often several-fold above baseline (about threefold over 24 hours by Day 5 in one small study), helping conserve protein; insulin low but still present; cortisol varies from person to person
Cellular Activity: Autophagy is the cell's built-in recycling system, and fasting is known to switch it on in animals; in people, some blood cells show signs of it during fasting, but nobody can yet say when it starts, when it peaks, or by how much
For many people hunger eases and thinking feels clearer around now, with a sense of calm, focus and control. Others feel no turning point; there is no fixed day.
What Is Known: fat use is high, ketones keep rising and the body is conserving protein. Repairs often promised for this stage (mitochondrial renewal, clearing damaged molecules, lower inflammation) have not been shown in people on a fast this long.
⚠️ Medical Supervision Required Beyond This Point
Cellular Activity: In mice, repeated multi-day fasts triggered blood stem cells to renew the immune system; that has not been shown in healthy adults. In a 10-day water fast, lysosomes (the cell's recycling centres) became more active, and inflammation markers rose too
Safety Requirements: Daily electrolyte monitoring, blood pressure tracking twice daily, medical oversight, careful attention to warning signs
Requires meticulous supplement protocol and professional medical guidance. Refeeding risk is higher after longer fasts: NICE counts more than 10 days with little or no food as high risk on its own. No study shows that benefits keep adding up as a fast gets longer.
The Metabolic Calculator provides realistic projections based on YOUR physiology—not generic estimates. Includes supplement recommendations, timing guidance, and safety checkpoints.
Calculate My TimelineExtended fasting depletes electrolytes rapidly. Electrolytes keep you upright and a blood pressure monitor tells you what your body is actually doing. Those are the two things worth having.
A safer extended fast starts with two things: the right electrolytes and a way to track your cardiovascular safety. We've split the kit into its two essential components so you get each from the best source — add both for the full protocol.
Autophagy Labs Fasting Salts — sodium, potassium, magnesium & B1 in one zero-calorie pouch. Sold by our sister store, Cellular Science.
Back soon — tell meA clinically-validated blood pressure monitor to track your vitals daily during the fast. Sourced via Amazon — see options below.
Choose a MonitorTwo components, two trusted checkouts — buy only what you need.
✓ Zero calories ✓ Zero sweeteners ✓ Zero fillers
4,000 mg sodium · 2,000 mg potassium · 400 mg magnesium · 100 mg thiamine (B1). Zero calories, sweeteners or fillers. Potassium and magnesium contribute to normal muscle function.
The last batch sold out and production is restarting. Leave your email and we will tell you once, the moment they are back.
Tell me when they’re back What is in it, and how to use it →✓ AFib screening ✓ 3× measurement averaging ✓ Intelli Wrap cuff ✓ Clinically validated
Screens for atrial fibrillation on every reading — the arrhythmia that electrolyte loss during a long fast can provoke. Takes three consecutive measurements and averages them. Cuff fits 22–42 cm.
✓ AFib screening ✓ App logging ✓ Pregnancy mode ✓ Clinically validated
Everything the X3 does, plus it logs to your phone — so you can hand your GP a trend rather than a memory. Validated for use in pregnancy and diabetes. Worth the difference for fasts beyond five days.
The fast itself lasts a few days. What you do around it decides how much of it lasts: how you eat afterwards, how you get through the hard days, and how you look after yourself.
A low-carb way of eating after the refeed keeps your body burning mostly fat, and ketogenic diets tend to take the edge off appetite, which can make the change easier to keep. It does not guarantee the weight stays off. For us it is the bridge from one fast to the next.
View Keto Protocol →Calming sound, such as singing bowls, helps some people ride out the stress of Days 2-3. Treat it as a way to relax: studies of music and the stress hormone cortisol give mixed results, and none has tested it during a fast.
Himalayan Echoes →Urge surfing and meditation for craving management. Hunger is a real body signal, and it comes in waves. Urge surfing means noticing the wave without acting on it; many cravings ease if you wait them out, though there is no fixed timetable.
Autophagy works from the inside; good skincare works on the surface. Two different jobs, both worth doing.
Autophagy Skincare →An anonymous check-in wall for people mid-fast: one line, stamped with the hour you are at. No account and no names, and every written note is read before it appears.
Be one of the first to check in
Next group fast: Sunday 8 November, 19:00, 5 days — start together, stop whenever you need to.
Honest answers to the questions everyone asks but few answer truthfully.