36-Hour Fast: An Hour-by-Hour Workday Plan
A 36-hour fast runs from dinner one evening to breakfast two mornings later: Sunday 7 pm to Tuesday 7 am. You eat a normal dinner, skip an entire day of food, sleep twice, and break the fast with breakfast. The main human trial of this pattern, Stekovic et al. (Cell Metabolism, 2019), found no adverse effects in healthy, non-obese adults doing strict alternate-day fasting for four weeks, with a cohort sustaining it over six months. Talk to your doctor before your first one.
Key Takeaways
- A 36-hour fast is one workday plus two nights of sleep. The hard part is Monday evening.
- The main human trial of 36-hour alternate-day fasting (n=60) allowed water, black coffee, and plain tea on fast days. No diet sodas, no "calorie-free" products.
- The "autophagy at hour 24" charts come from mouse studies. No one can give you a precise human timeline.
- Caffeine timing matters more than caffeine dose: your last cup needs to land at least six hours before Monday bedtime.
Who Should Not Try a 36-Hour Fast
This plan is for healthy adults. Johns Hopkins Medicine lists groups who should skip intermittent fasting: children and teens under 18, women who are pregnant or breastfeeding, people with type 1 diabetes who take insulin, and people with a history of eating disorders.
Add people with type 2 diabetes on glucose-lowering medication. A randomized trial (Corley et al., 2018) of 41 adults with type 2 diabetes found fasting increased hypoglycemia even after medication was reduced (RR 2.05, 95% CI 1.17 to 3.52). A 2019 Nutrients review called the evidence on fasting with diabetes "almost non-existent" and recommended it only under direct clinician supervision. Hopkins also notes that longer fasts of 24, 36, 48, and 72 hours "are not necessarily better for you, and may be dangerous."
Stop signs: dizziness or fainting, confusion, a racing heart, vomiting. Eat immediately. If symptoms persist, get medical help.
The 36-Hour Fast Schedule, Hour by Hour
| Clock Time | Fast Hour | What You're Doing | Physiology (Humans Only) | Evidence |
|---|---|---|---|---|
| Sun 7 pm | 0 | Last meal: protein, fiber, normal size | Digestion begins | -- |
| Sun 11 pm | 4 | Sleep | Liver glycogen fueling blood glucose | Rothman 1991 |
| Mon 7 am | 12 | Wake. Black coffee or tea | Gluconeogenesis supplying ~64% of glucose production | Rothman 1991 |
| Mon 7 to 11 am | 12 to 16 | Deep-work block | Lipid mobilization increasing | Stekovic 2019 |
| Mon 11 am to 3 pm | 16 to 20 | Meetings. Last caffeine by ~2 to 3 pm | Gluconeogenesis contribution still rising | Rothman 1991 |
| Mon 3 to 7 pm | 20 to 24 | Hardest stretch. Walk, water, salt | Gluconeogenesis reaches ~82% of glucose production (hours 22 to 36) | Rothman 1991 |
| Mon 7 to 11 pm | 24 to 28 | Evening routine, no dinner, no caffeine | Beta-hydroxybutyrate rising | Stekovic 2019 |
| Mon 11 pm | 28 | Sleep | Fat-derived metabolites elevated | Stekovic 2019 |
| Tue 7 am | 36 | Break the fast | 54 of 113 changed metabolites at least 20% higher, over 95% lipids or free fatty acids | Stekovic 2019 |
Shift the times to match your schedule. Keep the caffeine cutoff at least six hours before sleep.
What Actually Happens in Your Body by Hour 36
Your body does not flip a switch. It shifts gradually from stored glycogen to making its own glucose and burning fat.
Rothman et al. (1991) measured liver glycogen directly using ¹³C NMR during a 68-hour human fast. Gluconeogenesis supplied 64% (±5%) of glucose production through the first 22 hours, 82% through hours 22 to 36, and 96% after that. Glycogen tapers; it does not "run out" at a clean boundary.
The Stekovic metabolomics data adds the other half: at hour 36, 54 of 113 changed metabolites were at least 20% above fed values, over 95% of them lipids or free fatty acids. Beta-hydroxybutyrate was elevated even on non-fasting days in regular alternate-day fasters. More on fasting, ketones, and focus.
36-Hour Fast and Autophagy: Human Data vs. Mouse Data
The "autophagy starts at hour 24" claim traces to Alirezaei et al. (2010), which found short-term fasting produced "profound" neuronal autophagy in mice. Not humans.
A randomized trial that measured autophagic flux in humans is Bensalem et al. (Journal of Physiology, 2025): n=121 adults with obesity, over six months. The authors noted that nutrient-restriction autophagy "has never been shown in humans" before their study. Their finding: a between-group difference in post hoc analysis only (P=0.04), with no within-group rise from baseline.
Nobody can tell you the hour autophagy starts in a person, and there is no validated home test. If someone gives you a precise timeline, ask whether the data came from mice or humans.
Can You Have Coffee on a 36-Hour Fast?
Yes. The Stekovic protocol allowed water, flavored carbonated water, black or green tea (no sweetener), and coffee. It excluded diet sodas and "calorie-free" products. More detail: does black coffee break a fast and which teas are fine on a fast.
The harder question is when to stop. A randomized crossover trial (Drake et al., 2013) of 12 healthy sleepers found that 400 mg of caffeine six hours before bedtime still cut measured sleep by over an hour. Monday night is when you are hungry, restless, and most vulnerable to poor sleep. Plan your last caffeine at least six hours before bedtime; longer-acting sources need eight hours. The FDA cites 400 mg per day as an amount not generally associated with negative effects for most adults, but during a fast, less is smarter: on an empty stomach, caffeine can hit faster. See also: how caffeine affects deep sleep.
How to Get Through the Monday Evening
Hours 20 to 28 are when most people want to quit. You skipped dinner, you are home, and every habit says "eat."
- Walk 20 to 30 minutes. Gets you out of the kitchen.
- Schedule something for your hands. A phone call, a chore, anything that is not sitting near food.
- Water and a pinch of salt. Electrolyte losses are real during extended fasts.
- Go to bed at your normal time. Going early because you are bored backfires: you lie awake fixating on food.
Headaches and fatigue are common the first time. They usually come from dehydration, electrolyte shifts, or caffeine withdrawal. For specific fixes: why fasting gives you a headache and why you feel tired while fasting.
How to Break a 36-Hour Fast
Tuesday 7 am. Eat a normal-size breakfast with protein: eggs, yogurt, oats with nuts. Eat slowly. No trial has compared refeed methods at 36 hours, so precise protocols are speculation. Refeeding syndrome belongs to prolonged starvation, not a day and a half in a healthy adult. For a broader look: what breaks a fast, goal by goal.
How Often Should You Do a 36-Hour Fast?
The only human data on repeated 36-hour fasts comes from alternate-day fasting. Stekovic et al. ran a four-week RCT plus a cohort doing it for over six months, with no reported adverse effects.
Adherence is the bottleneck. Trepanowski et al. (JAMA Internal Medicine, 2017) randomized 100 adults for one year: the alternate-day group had the highest dropout (13 of 34, 38%) and participants ate more than prescribed on fast days. Once a week (the "monk fast") is a common pattern but has not been tested in a trial. Start with one, see how you respond, and talk to your doctor before making it routine.
The Hard Part Is One Evening, Not 36 Hours
A 36-hour fast sounds extreme. In practice, you sleep through nearly half of it. The workday fills another third. What remains is one evening without dinner and one delayed breakfast.
The physiology is a smooth gradient from glycogen toward gluconeogenesis and fat oxidation, not a switch at some magic hour. The autophagy timelines on social media come from mice, and the one randomized human trial found only a post hoc difference. That does not mean fasting is useless. It means the honest case rests on the metabolic data we have, not the timelines we wish we had. Plan your caffeine cutoff, plan your Monday evening, and talk to your doctor first.
Frequently Asked Questions
Is a 36-hour fast safe?
For healthy adults without the conditions listed above, the Stekovic trial reported no adverse effects over four weeks or in a cohort fasting over six months. Johns Hopkins notes longer fasts "are not necessarily better for you, and may be dangerous." Talk to your doctor first.
What can you drink on a 36-hour fast?
Water, flavored carbonated water, black or green tea (no sweetener), and black coffee per the Stekovic protocol. Diet sodas and "calorie-free" products were excluded.
When does autophagy start on a 36-hour fast?
No one knows the hour in humans. The "24-hour" figure comes from mouse research (Alirezaei et al., 2010). A randomized human trial (Bensalem et al., 2025) found only a post hoc between-group difference. No home test exists.
How do you break a 36-hour fast?
Normal-size breakfast with protein. Eat slowly. No trial has compared refeed strategies at this duration. Refeeding syndrome applies to prolonged starvation, not 36 hours.
Can you work out during a 36-hour fast?
Light walking is fine. Skip heavy training on a first fast. Liver glycogen is running low and most of your glucose is coming from gluconeogenesis, so expect hard sessions to feel harder.
Is a monk fast the same as a 36-hour fast?
Yes. "Monk fast" is informal shorthand for the same dinner-to-breakfast-two-days-later protocol. It is not a clinical term.
Caffeine for the Workday, Not the Night Inside the Fast
The central tension of this article: caffeine helps the Monday deep-work block and can ruin Monday night's sleep.
Roon is a zero-calorie, zero-sugar oral pouch with 80 mg caffeine, 60 mg L-theanine, 25 mg methylliberine (Dynamine), and 5 mg theacrine (TeaCrine). It contains sucralose, so it falls outside the strictest "water, coffee, and tea only" protocols, including the Stekovic fast-day rules. Be clear with yourself about where you draw that line.
Why duration matters here: in a randomized, double-blind crossover PK study (n=12), co-administration of methylliberine with caffeine cut caffeine's oral clearance from 41.9 to 17.1 L/hr and extended its half-life from 7.2 to 15 hours with no higher peak (study). That study used 100 mg methylliberine + 150 mg caffeine, roughly 4x the methylliberine and 2x the caffeine in a Roon pouch; the magnitude at Roon's doses is unpublished. The direction is the same: one morning pouch is designed for a 6 to 8 hour felt window, no second dose needed. That longer tail is also why Roon's guidance is to stop at least 8 hours before bed.
From $9.16 per tin on a 12-tin subscription ($0.61 per pouch). If you want one measured dose for the Monday work block, try Roon in the morning, and talk to your doctor before your first 36-hour fast.
Related from Roon
- Does Coffee Break a Fast?
- Does Tea Break a Fast?
- Fasting Headache: Causes and Fixes
- Intermittent Fasting and Focus: The Ketone Connection
Written by Roon Team
