16/8 Fasting: How It Works and How to Start

In 30 seconds

16:8 intermittent fasting means fasting for about 16 hours and eating within an 8-hour window each day, for example from noon to 8 pm. In trials it led to modest weight changes, broadly similar to other fasting schedules, so it isn’t proven best for everyone. If 8 hours feels abrupt, build up from 12:12 or 14:10.

• 16:8 is a daily eating window: about 16 hours of fasting and 8 hours to eat, much of the fast overnight.
• Trials found modest weight and cardiometabolic effects, broadly similar across fasting schedules.
• An earlier window improved glucose and insulin measures in small, short trials; results vary.
• Short biomarker studies don't show when autophagy starts during a 16:8 fast.

How does 16:8 work?

You eat within an 8-hour window and fast for the other 16 hours. If your last meal ends at 8 pm, your fast runs until noon the next day, and much of it happens while you sleep.

The 16:8 schedule is a time-restricted eating pattern with about 16 hours of fasting and an 8-hour daily eating window.Source 22

A sample 16:8 day

1. 8 pm to noon, about 16 hours

   Fasting

   No calories outside the window; much of it falls overnight.

2. Noon to 8 pm, about 8 hours

   Eating window

   Meals and caloric drinks stay inside the window.

Try a schedule

Example times. Nothing is saved.

Schedule

12:1214:1016:818:620:4

Last meal

8:00 PM

Fasting

16 h

Eating window

8 h

Fast ends

12:00 PM

Eating window: 12:00 PM to 8:00 PM. Hours on a clock are not a measurement of your body.

Open the fasting calculator

What does the research show?

Trials of 16:8 and other daily eating windows point the same way: modest changes, broadly similar to other fasting schedules.

Randomized-trial syntheses found that time-restricted eating schedules, including 16:8, led to modest weight loss and changes in cardiometabolic risk factors. Results depended on trial definitions, adherence and duration, and no single fasting schedule was proven better across all trials.Source 11

Is an earlier eating window better?

Possibly, for blood sugar, but the evidence is early. Studies that moved the window earlier in the day saw better glucose measures, and the early vs late eating window guide looks at this in more detail.

Earlier eating windows improved insulin sensitivity and 24-hour glucose in small randomized trials, and some findings appeared independent of weight loss.Source 33Source 44Source 22

A review of time-restricted eating trials found that when people eat, earlier or later, can influence metabolic outcomes, but differences between trials mean no single best window is established for everyone.Source 22

Controlled-feeding and short crossover trials found that earlier windows improved insulin sensitivity and 24-hour glucose and shifted gene-expression markers linked to cellular processes. They were small and short, so they don't show long-term or wider effects.Source 33Source 44

What about autophagy? Those gene markers are a hint, not a measurement.

Short biomarker studies report changes in gene-expression markers related to autophagy, but these measures don't show when autophagy begins during a fast.Source 44

How to build up to 16:8

If eight hours feels abrupt, start with 12:12 or 14:10 and move one boundary at a time. Keep meals adequate inside your window, and if the routine isn’t sustainable, go back to a gentler pattern.

Who should check with a clinician first?

Talk to a qualified health professional before fasting if you are pregnant or breastfeeding, under 18, living with or recovering from an eating disorder, have diabetes, take insulin or a medicine affected by meal timing, are an older adult, or are acutely ill. Do not change the dose or timing of any medicine without your clinician. See Blimbi’s safety guide.

Related guides

• 20:4 Intermittent Fasting: How It Works

  20:4 intermittent fasting means about 20 hours of fasting and a 4-hour eating window. See a sample day, what trials found and when a gentler schedule wins.

• 12:12 Intermittent Fasting: How It Works

  12:12 intermittent fasting pairs a 12-hour eating window with a 12-hour fast. See a sample day, what trials found and who should ask a clinician first.

• Intermittent Fasting Schedule: Common Options Compared

  Compare intermittent fasting schedules: 12:12, 14:10, 16:8, 18:6, 20:4 and 5:2. Trials found similar average effects, so pick one you can keep.

• Is Blimbi a Free Intermittent Fasting App?

  Free fasting app for iPhone and Android: timer, journal, reminders and CSV export with no ads. Sign in with Apple or Google; Blimbi Plus is optional.

Next steps

• Find a fasting schedule for your day

  Answer 3 quick questions and get a fasting schedule to try, with times that fit your day.

• When does my fast end?

  See the time remaining and an educational timeline. Hours on a clock are not a measurement of your body.

• Take the fasting quiz

  A few questions about your day, then a gentle place to start.

• Intermittent fasting protocols

  Compare the common schedules side by side.

Frequently asked questions

Will 16:8 help me lose weight?

Trials found modest average weight loss with daily eating windows, including 16:8, broadly similar to other fasting approaches. Results vary between people, and over time they depend on how consistently you follow it and how much you eat overall.Source 11

What is the best time for a 16:8 eating window?

There's no proven best window. Small, short trials found earlier windows improved insulin sensitivity and 24-hour glucose compared with later ones, but results vary between trials. An earlier window may help some people; one that fits your day matters too.Source 33Source 44Source 22

Does 16:8 trigger autophagy?

Current evidence can't say. Short studies saw changes in gene-expression markers linked to autophagy, but those markers don't measure autophagy across the whole body or show when it starts.Source 44

Who should not do 16:8?

Talk with a clinician first if you have diabetes or take medicines that affect blood sugar, are pregnant or breastfeeding, are under 18, or have a history of disordered eating. Get medical help for severe dizziness, fainting, confusion or other worrying symptoms.Source 11Source 22Source 55Source 66Source 77

Sources

1. 1

   Intermittent fasting strategies and their effects on body weight and other cardiometabolic risk factors: systematic review and network meta-analysis of randomised clinical trialsZhila Semnani-Azad et al. BMJ, June 18, 2025.DOI: 10.1136/bmj-2024-082007 · PMID: 40533200Systematic review and meta-analysis

2. 2

   Effects of timing and eating duration of time restricted eating on metabolic outcomes: systematic review and network meta-analysisYu-En Chen et al. BMJ, January 21, 2026.DOI: 10.1136/bmjmed-2024-001071 · PMID: 41586347Systematic review and meta-analysis

3. 3

   Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with PrediabetesElizabeth F. Sutton et al. Elsevier BV, June 5, 2018.DOI: 10.1016/j.cmet.2018.04.010 · PMID: 29754952Human randomized trial

4. 4

   Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in HumansHumaira Jamshed et al. MDPI AG, May 30, 2019.DOI: 10.3390/nu11061234 · PMID: 31151228Human randomized trial

5. 5

   Fasting Safely with DiabetesMartin M. Grajower. National Institute of Diabetes and Digestive and Kidney Diseases, August 26, 2020.Official guidance

6. 6

   Weight gain in pregnancyNHS. NHS, July 6, 2022.Official guidance

7. 7

   Overview – Eating disordersNHS. NHS, January 23, 2024.Official guidance