12:12Entry-level
Fast 12 hours, eat within 12. Often used as an entry-level pattern that is close to how many adults already eat.
Example schedule
Eat 8:00 AM – 8:00 PM · Fast 8:00 PM – 8:00 AM
By ONE Editorial Team · Last updated: September 4, 2026
Intermittent fasting is an eating pattern that alternates periods of eating with periods of fasting. Instead of prescribing a specific list of foods, it focuses mainly on when you eat. Different approaches use different fasting and eating windows, from daily time-restricted eating to schedules that vary across the week.
Research suggests intermittent fasting can help some people manage weight and improve certain metabolic health markers, but it is not a universal solution and it is not clearly superior to every other calorie-reduction approach.
Intermittent fasting is an eating pattern that alternates defined periods of eating with periods of fasting. Rather than dictating a specific list of foods, it is primarily concerned with when you eat.[1][2]
The most familiar form is time-restricted eating, in which you eat during a set window each day and fast the rest of the time. Common daily patterns compress eating into anywhere from a 4-hour to a 10-hour window. Other approaches restrict calories on specific days of the week or alternate between eating and fasting days.
Because intermittent fasting is an umbrella term rather than a single protocol, no strict food rule defines it. What you eat still matters — nutritional quality, adequate protein, and overall energy intake all influence how your body responds to any eating schedule. Intermittent fasting does not mean starvation and it does not require extreme restriction.
Some people find that a defined eating window naturally reduces snacking and late-night eating, which can result in lower overall energy intake. Others find the schedule easier to plan around work and family life than counting portions at every meal. The core idea is structure: choosing when you eat and when you don't on purpose.[1]
After a meal, the body absorbs nutrients and uses them for immediate energy needs. Excess energy is stored — some as glycogen in the liver and muscles, some as body fat. Insulin, the hormone that helps cells absorb glucose, rises during and shortly after eating.
When you do not eat for several hours, insulin gradually falls and the body shifts toward greater use of stored energy. As the fast continues, liver glycogen is drawn down and fatty acids are increasingly mobilised as fuel. With longer fasts, ketones — produced from fat breakdown — become a larger contributor to the fuel mix.[6]
These changes are gradual and continuous. There is no universal metabolic clock that changes state at the exact same hour for every person. How long each transition takes depends on factors including your most recent meals, glycogen availability, activity level, individual metabolic health, and the length of the fast.[1]
ONE's simplified fasting timeline
To make progress easier to follow inside the app, ONE groups the transition into five simplified tracking phases. These ranges are used by ONE to make fasting progress easier to understand — they are not universal biological thresholds. Human metabolism changes continuously, and the exact timing of metabolic processes varies from person to person.
Intermittent fasting comes in many variations, from daily time-restricted eating to schedules that change across the week. Below are the patterns most often discussed. None is inherently “best” — the right approach depends on lifestyle, health status, and what a person can sustain over time.[2]
Fast 12 hours, eat within 12. Often used as an entry-level pattern that is close to how many adults already eat.
Example schedule
Eat 8:00 AM – 8:00 PM · Fast 8:00 PM – 8:00 AM
Fast 14 hours, eat within 10. A modest step up from 12:12 for people who want a slightly longer daily fast.
Example schedule
Eat 10:00 AM – 8:00 PM · Fast 8:00 PM – 10:00 AM
Fast 16 hours, eat within 8. The most commonly cited time-restricted eating pattern in the popular literature.
Example schedule
Eat 12:00 PM – 8:00 PM · Fast 8:00 PM – 12:00 PM
Fast 18 hours, eat within 6. A more compressed daily eating window.
Example schedule
Eat 1:00 PM – 7:00 PM · Fast 7:00 PM – 1:00 PM
Fast 20 hours, eat within 4. A short daily eating window; sometimes called a "warrior"-style pattern.
Example schedule
Eat 4:00 PM – 8:00 PM · Fast 8:00 PM – 4:00 PM
Eat normally on five days per week and restrict calories (commonly around 500–600 kcal) on two non-consecutive days.
Example schedule
Normal: Mon Tue Thu Sat Sun · Low-cal: Wed & Fri
"One meal a day." All daily energy intake is consumed within a single meal, followed by an extended fasting window.
Example schedule
Eat 6:00 PM – 7:00 PM · Fast the remaining 23 hours
Intermittent fasting can help some people lose weight, mainly when the eating pattern results in a lower overall energy intake. Recent systematic reviews and meta-analyses suggest intermittent fasting strategies can produce meaningful reductions in body weight in adults with overweight or obesity, though the size of the effect varies across studies and populations.[3][4] The evidence does not support the claim that intermittent fasting is universally superior to standard continuous energy restriction for weight loss. Many analyses find that outcomes are broadly comparable when overall calorie intake is similar.[3]
Some studies report improvements in measures such as fasting glucose, triglycerides, blood pressure, and certain insulin-related markers. Effects vary by study, by fasting approach, and by the population studied.[4][5] For people with metabolic risk factors, structured eating patterns of any kind — including but not limited to intermittent fasting — that produce sustained calorie reduction may improve these markers.
Most randomised trials of intermittent fasting are relatively short, typically running from a few weeks to a few months. Protocols vary widely, from daily time-restricted eating to alternate-day fasting to 5:2-style schedules. As a result, the evidence base for long-term adherence, long-term maintenance of results, and long-term head-to-head comparisons with continuous energy restriction is still developing.[5][6]
Not necessarily. Both intermittent fasting and continuous calorie restriction can produce weight loss when they lead to a sustained calorie deficit, and both can improve certain metabolic markers. Systematic reviews comparing intermittent fasting with continuous energy restriction generally show that weight-loss outcomes are broadly similar, with small differences that vary by protocol, outcome measure, and study population.[3][4]
Where intermittent fasting may have an edge for some people is adherence — a clearly defined eating window can be simpler to follow than counting calories at every meal. Where it may be harder for others is with social schedules, exercise timing, or the risk of overeating during the eating window. The best approach is usually the one a person can actually sustain over months and years — not the one that produces the largest short-term change on a chart.
Intermittent fasting is not appropriate for everyone. People considering it should speak with a qualified healthcare professional first, particularly if they:
Adverse effects during the adjustment period can include hunger, fatigue, headaches, irritability, and difficulty concentrating. These often improve as the body adapts, but they can also be a signal that a particular schedule is not right for a given person.[1][2]
Important
ONE is a fasting and wellness tracking tool. It does not provide medical diagnosis or replace advice from a qualified healthcare professional.
If you and your healthcare provider decide intermittent fasting is a reasonable approach for you, a few general principles help:
For a practical walkthrough, see our guide to how to start intermittent fasting.
ONE is an intermittent fasting app for iOS and Android that helps you follow your fasting routine and see your progress over time.
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Intermittent fasting is an eating pattern that alternates defined periods of eating with periods of fasting. It focuses on when you eat rather than dictating a specific list of foods, and it can be structured in many different ways.
There is no single correct fasting length. Common daily patterns range from 12 to 20 hours of fasting per day; less-frequent approaches such as 5:2 restrict calories on specific days rather than each day. The right length depends on lifestyle, health status, and how well a given schedule is tolerated.
16:8 (fasting for 16 hours and eating within an 8-hour window) is often recommended as an accessible starting point, in part because part of the fasting window overlaps with sleep. Some people find a shorter fasting window such as 12:12 or 14:10 easier to adopt first before moving to 16:8.
Yes. Plain water, unsweetened tea, and black coffee are commonly consumed during the fasting window. Adequate hydration is generally recommended throughout the day.
Intermittent fasting can support weight loss for some people, mainly when the eating pattern results in a lower overall calorie intake. Systematic reviews generally find that weight loss on intermittent fasting is broadly comparable to continuous calorie restriction when overall energy intake is similar.
Current evidence does not support the claim that intermittent fasting is universally better than continuous calorie restriction. Both approaches can produce weight loss when they create a sustained energy deficit. Which is easier to maintain depends on the individual.
No. Intermittent fasting is not recommended for people who are pregnant or breastfeeding, have a history of an eating disorder, are underweight or malnourished, experience hypoglycemia, or have medical conditions or medications affected by eating timing. Speak with a qualified healthcare professional before starting.
Autophagy is a normal cellular process influenced by nutrient availability, energy status, and other factors. Current human evidence does not support assigning a single exact fasting hour at which autophagy universally 'switches on' for every person. It is a continuous, context-dependent process rather than a fixed clock.
Prepared by the ONE Editorial Team using peer-reviewed research and guidance from established medical institutions.