Clear, practical guides to intermittent fasting: how the main schedules work, what to eat, what research does and does not show, and who should not fast. Plus a free fasting timer that runs in your browser.
Start Here (Beginners) Find Your ProtocolThe most common fasting schedules, from daily eating windows to weekly approaches. Most beginners start with a daily window such as 12:12 or 16:8. Pick one that fits your schedule, and check the safety notes first.
Fast 16 hours, eat in an 8-hour window, for example noon to 8pm. A common starting point for beginners. Already comfortable with 16:8? See the 18:6 guide.
Read 16:8 GuideOne meal a day, with a fast of about 23 hours. Simple, but demanding, and it is hard to get enough nutrition in a single meal.
Read OMAD GuideEat normally five days a week and limit calories to roughly 500–600 on two non-consecutive days. Some people find it easier to fit around social life than daily fasting.
Read 5:2 GuideAlternate fasting or very-low-calorie days with normal eating days. More demanding than daily schedules and not suitable for everyone.
Read ADF GuideFasting on water only for a day or longer. Longer water fasts carry real risks and should only be done with medical supervision.
Read Water Fast GuideOne or two 24-hour fasts per week, with normal eating on the other days. A flexible weekly approach.
Read Eat Stop EatWhat research suggests so far, including where the evidence is limited. Most studies are small and short-term, and results vary from person to person.
Weight loss with fasting appears to come mainly from eating less overall. Trials comparing it with ordinary calorie restriction generally find similar results. Weight loss guide →
Fasting increases autophagy in animal and cell studies. In humans it is hard to measure, and there is no established timeline. Autophagy explained →
Some people report steady energy and focus while fasting; others feel tired or irritable, especially at first. Experiences vary.
Fewer meals to plan, prepare, and clean up. Many people like the simple structure.
Some studies have found modest improvements in insulin and blood sugar measures, often alongside weight loss. People with diabetes need medical advice before fasting. Diabetes & fasting →
Eating enough protein and doing resistance training help preserve muscle, whatever your eating schedule. Muscle & fasting →
The fasting hours get most of the attention, but what you eat during your eating window matters just as much.
Simple, balanced ways to end a fast, and why a very large first meal can leave you uncomfortable.
How to Break a FastSample weekly meal plans for 16:8, OMAD, and 5:2 — with portion guidance and grocery lists.
View Meal PlansWhat breaks a fast and what doesn’t, including milk, cream, MCT oil, and sweeteners.
Coffee & FastingSodium, potassium, and magnesium: why they matter on longer fasts and when to be careful.
Electrolyte GuideHow ketogenic eating and fasting overlap, the extra side effects to watch for, and who should avoid combining them.
Keto + FastingProtein, nutrient density, hydration, and meal timing inside your eating window.
Nutrition GuidesTrack a fast from 16 to 48 hours. It runs in your browser with no signup or account, and your history is stored only on your device. Fasts longer than 24 hours carry more risks; get medical advice first.
Total Fasts
Average Duration
Longest Fast
No fasting history yet. Complete your first fast to see your statistics!
Real situations: starting from scratch, fasting around work, family meals, training days, and when something feels off.
A step-by-step first month — from your first 12-hour fast to a comfortable 16:8 routine.
Start HereHeadaches, fatigue, sleep changes, irritability — what causes them and how to handle them.
TroubleshootEnergy management, meeting culture, lunchtime workarounds, and avoiding awkward conversations.
Workplace GuideCooking for non-fasters, dinners out, holidays, and explaining your eating schedule.
Family GuideWhen to train, what to train for, and how to fuel performance inside an eating window.
Training GuideHormonal considerations, menstrual cycle timing, and protocol modifications worth knowing.
Women’s GuideWhich medications need food, which interact with fasting, and what to discuss with your doctor.
Medications GuideHow fasting windows affect sleep onset, depth, and recovery — and how to schedule meals for better rest.
Sleep GuideWho should not fast, warning signs to stop immediately, and conditions that need medical supervision.
Safety GuideFifteen common mistakes that stall progress or make fasting harder, with a practical fix for each.
Mistakes GuideHow fasting interacts with specific conditions, hormonal contexts, and the symptoms most worth understanding properly.
What research suggests about fasting and blood pressure, and why medication needs a doctor’s review.
BP GuideWhat is known about fasting and PCOS, cycle tracking, and when to talk to your doctor.
PCOS GuideThyroid medication timing, how fasting affects thyroid tests, and common myths.
Thyroid GuideWhat research suggests about fasting and digestion, and why people with IBS or IBD need individual advice.
Gut GuideWhy fasting with diabetes needs medical supervision, the risk of low blood sugar, and what research shows.
Diabetes GuideWhat fasting actually does to cortisol, and the “adrenal fatigue” confusion.
Cortisol GuideWhat research suggests about fasting, weight loss, and liver fat, and the role of medical care.
Fatty Liver GuideHow cholesterol results may change with fasting, and why some people see LDL rise.
Cholesterol GuideWhy skipping meals can trigger migraines, what research shows, and precautions if you have migraine.
Migraine GuideHow fasting may affect mood, when to avoid it, and medication considerations.
Mood GuideWhat research shows on fasting and inflammation, and why it is not a treatment for autoimmune disease.
Inflammation GuideWhat research on fasting during cancer treatment does and does not show. Any change should be discussed with your cancer care team.
Cancer GuideWhy caution is needed, the risk of symptom crashes, and what is still unknown.
Long COVID GuideFasting in specific life stages and contexts where the standard advice doesn’t quite fit.
Hormonal changes, what research suggests, and gentler approaches to consider.
Menopause GuideWhat is known about fasting and fertility, and when to talk to your doctor.
Fertility GuideWhy fasting is generally not recommended for teens — for parents searching about it.
Teen GuideSpecific guides for the major training contexts — what fasted training actually does and which sessions to fuel.
Building muscle while losing fat: when it’s realistic and the basics that matter.
Recomp GuideWhat fasted cardio does and doesn’t do, including the “burn more fat” question.
Fasted CardioFueling long training sessions and races around an eating window.
Endurance GuideWhere fasting fits in prep timeline, peak week, and post-show recovery.
Contest PrepWhich pre-workout ingredients break a fast, caffeine limits, and safety notes.
Pre-WorkoutDetailed guides for specific fasting structures and the approaches you’ll encounter online.
Side-by-side comparison of the main daily schedules and how to choose.
Compare ProtocolsA longer fast than daily schedules: what it involves, the risks, and who should avoid it.
36-Hour FastA 5-day very-low-calorie plan: what it involves, what research shows, and safety.
FMD GuideWhy this extreme approach is risky and what to know before considering long fasts.
Snake DietHow fasting compares with other common approaches, and when combining them may make sense.
What head-to-head trials show and which approach suits which person.
vs CountingHow the two approaches differ, what they have in common, and the trade-offs of combining them.
vs KetoA well-studied eating pattern compared with a meal-timing approach, and how they can fit together.
vs MediterraneanHow fasting differs from GLP-1 medications, and why any combination needs your prescriber’s input.
vs GLP-1Knowing whether fasting is working, what to measure, and what to ignore.
What to measure, what to ignore, and how long to give a new routine.
Diagnostic GuideBlood tests to discuss with your healthcare provider and how fasting can affect results.
BloodworkCombining scale weight, measurements, and other tracking methods.
Tracking MethodsWhat breaks a fast, what doesn’t, and what is and isn’t worth using.
What research shows, the safety concerns, and whether it’s worth using.
ACV GuideWhich sweeteners are likely to affect a fast, which are not, and what research says.
Sweeteners GuideWhen protein powder is useful, the main types, and whether it breaks a fast.
Protein PowderWhat greens powders contain, what they can and can’t replace, and whether they break a fast.
Greens ReviewWhat breaks a fast, what doesn’t — including butter coffee, MCT oil, milk.
Coffee GuideFasting has to fit your life — alcohol, travel, age, budget, diet style. Practical guides for the situations that actually come up.
Why alcohol can hit harder after fasting, its effect on sleep and calories, and safer choices.
Alcohol GuideManaging meal timing, hydration, and fasting schedules across time zones.
Travel GuideCheap, nutrient-dense eating, sample grocery list, and what to skip from the wellness aisle.
Budget GuideHitting protein targets on plants in a compressed eating window — strategy and food list.
Vegan GuideAutophagy, ketosis, gluconeogenesis, refeeding — every term used on this site, defined plainly.
GlossarySummaries of notable fasting studies, what they measured, and their limits.
ResearchHunger waves, decision fatigue, and the mental side of changing how you eat.
PsychologyWhich measurements are useful, which to ignore, and how to review your progress.
TrackingIntermittent fasting is a pattern of eating that cycles between set periods of eating and fasting. It focuses on when you eat rather than which foods you eat. Common approaches include 16:8 (16 hours fasting, 8 hours eating), 18:6, OMAD (one meal a day), 5:2 (five days of normal eating and two reduced-calorie days each week), and alternate-day fasting.
Many beginners start with a 12-hour overnight fast and build up to 16:8, for example eating between 12pm and 8pm and fasting overnight. It fits around most work and family meal routines. The best schedule is one you can follow comfortably while still eating balanced meals.
Black coffee, plain tea, and water have little or no calories and are generally considered fine during a fast. Milk, cream, sugar, and sweetened syrups add calories and break a fast. If you want a strict fast, avoid sweeteners and flavored drinks as well.
It varies from person to person. Many people find the fasting period gets easier after the first week or two. Any weight change usually happens gradually over weeks to months and depends mostly on how much you eat overall, what you eat during your eating window, sleep, and activity. Changes in blood markers, if any, are best checked with your healthcare provider.
Intermittent fasting is not recommended for people who are pregnant or breastfeeding, people with a history of eating disorders, people who are underweight, and children and teenagers. People taking insulin or sulfonylureas, or who have other medical conditions or take regular medication, should only fast with medical supervision. Talk to a healthcare professional before starting.
Read the beginner guide, choose a schedule that fits your life, and use the free timer to track it. Everything on this site is free.
Beginner Guide Open TimerFreeFasting is educational. It is not medical advice. Consult a qualified healthcare professional before starting any fasting protocol, especially if you take medication, are pregnant, or have a medical condition.