How to Start Intermittent Fasting

Start intermittent fasting with a 12-hour overnight fast and a 12-hour eating window, making a complete cycle of 24 hours. An intermittent fasting timer can help you keep track of both windows.

What is intermittent fasting?

Intermittent fasting is an eating pattern that alternates periods of eating with periods of fasting. A common approach is time-restricted eating: you eat during a set window each day and avoid food outside it. The fasting period can include time spent sleeping.

Intermittent fasting is not necessary for health, and it does not require a particular diet. Its usefulness depends partly on whether the schedule helps you eat well and fits your life without causing distress or symptoms.

Despite claims about fasting for detox, fasting is not needed to cleanse the body. The liver and kidneys do most of the body's detoxification; the lungs and gut help eliminate waste, and sweat removes only trace amounts. Drinking enough water supports normal body function during a fast.

How do you start intermittent fasting?

1. Check whether fasting is appropriate for you. Do not start on your own if you are pregnant or breastfeeding, under 18, underweight, or have a current or past eating disorder. If you have diabetes, another medical condition, or take medication that may be affected by fasting, speak with a clinician first; the safety section below explains why.

2. Choose a 12-hour overnight fast. For example, finish your evening meal at 7 p.m. and have breakfast at 7 a.m. the next day. That leaves a 12-hour eating window from 7 a.m. to 7 p.m. and a 12-hour fasting window from 7 p.m. to 7 a.m. Shift the times to suit your sleep, work, and family routine.

3. Plan meals that fit the eating window. Include regular meals with foods such as vegetables, fruit, whole grains, protein sources, and healthy fats. You do not need to skip a meal simply because you are fasting overnight. Plan enough food to meet your needs rather than treating the eating window as a reason to eat as little as possible.

4. Drink during the fast. Water is a practical choice, and plain tea or black coffee can also fit a fast. Avoid putting yourself on a dry fast: intermittent fasting does not require avoiding water. If a clinician has told you to limit fluids, follow that advice rather than a general fasting plan.

5. Notice how the schedule feels. Pay attention to hunger, energy, sleep, concentration, and whether you can comfortably take part in normal activities. Mild hunger may occur when your routine changes, but feeling unwell is not a sign that you need to push through. Stop the fast if you feel dizzy, weak, shaky, or otherwise unwell.

6. Adjust only if the routine works for you. If a 12-hour fast feels manageable and you want a longer fasting period, you could try a 14-hour fast with a 10-hour eating window. Move the start or end time gradually, and keep meals adequate. There is no requirement to progress to a longer fast, and a longer fast is not automatically better.

7. Reassess rather than forcing the schedule. Consider whether intermittent fasting is helping you maintain a practical routine without excessive hunger, missed nutrition, or preoccupation with food. If it disrupts work, sleep, exercise, or social meals, shorten the fast or return to your usual eating schedule. You can choose another approach if fasting is not a good fit.

How often should you practice intermittent fasting?

A 12-hour overnight schedule can be repeated daily if it suits you, but you do not have to follow it every day. Some people prefer a consistent schedule; others find it easier to adjust their eating window around work, travel, or family events. Missing a day does not mean you need to compensate with a longer fast.

Other patterns vary considerably in how restrictive they are:

• 16:8 intermittent fasting uses a 16-hour fast and an 8-hour eating window. It is an option, not a required next step.
• The OMAD diet concentrates eating into one meal a day. It is more restrictive and is not a sensible starting point for most beginners.

Choose a pattern that leaves room for adequate meals and hydration. If even a shorter fasting window makes it difficult to eat enough or feel well, it is reasonable not to fast.

What benefits can intermittent fasting offer?

For some adults, intermittent fasting can provide structure that makes their eating routine easier to manage. It may also help with weight loss, although results differ and weight loss is not guaranteed.

A 2025 systematic review and network meta-analysis of 99 randomized trials found that intermittent fasting strategies and continuous calorie restriction reduced body weight compared with unrestricted diets. Overall, the findings do not establish a simple daily eating window as a clearly superior weight-loss method to conventional calorie restriction.

A 2020 systematic review also noted that many intermittent fasting studies were small or short. More long-term research is needed to understand how well people can sustain these patterns and their effects over time. Findings from studies of different fasting schedules should not be assumed to apply equally to a beginner's 12-hour overnight fast.

Who should avoid intermittent fasting, and when should you stop?

Avoid intermittent fasting if you are pregnant or breastfeeding, are a child or teenager, are underweight, or have a current or past eating disorder, unless your healthcare professional specifically advises otherwise. Restricting when you eat can make it harder to meet nutritional needs or may worsen an unhealthy relationship with food.

Talk with a clinician before starting if you have diabetes, kidney disease, another chronic condition, or take medication. This is especially important for insulin or medicines that can lower blood sugar, as well as medicines that need to be taken with food. Do not stop, skip, or change medication to fit a fasting schedule; ask the prescriber for an appropriate plan.

Stop fasting if you develop dizziness, shakiness, weakness, unusual fatigue, or other symptoms that concern you. Eat and drink as appropriate, and contact a healthcare professional if symptoms persist, recur, or you are unsure what caused them. If you suspect low blood sugar, treat it promptly with a quick source of sugar according to your clinician's plan; do not wait for the fasting window to end.

Seek emergency help for fainting, severe confusion, or an inability to swallow. Do not give food or drink by mouth to someone who is unconscious or unable to swallow safely.