Guide
16:8 intermittent fasting, explained
16:8 is the most popular way to do intermittent fasting.1 You go 16 hours without food and eat within the other 8. It sounds hard, but most of those 16 hours happen while you’re asleep.
What 16:8 means
The two numbers are hours. 16 is how long you fast. 8 is your eating window. If you finish dinner at 8 pm and eat again at noon the next day, that’s 16:8.
You don’t eat less food than usual on purpose. You just eat it within a shorter part of the day.
A sample day
| Time | What happens |
|---|---|
| 12:00 | First meal. Your eating window opens. |
| 16:00 | A snack, if you want one. |
| 19:30 | Dinner, your last meal of the day. |
| 20:00 | Your eating window closes and the fast starts. |
| 23:00 – 07:00 | Sleep. That’s 8 of your 16 hours done. |
| Morning | Water, black coffee or plain tea. |
| 12:00 | 16 hours. The fast ends with your first meal. |
The times aren’t fixed. If your mornings start early, try eating from 9 am to 5 pm instead. What matters is keeping roughly the same times each day.
What you can drink while fasting
- Yes: water, sparkling water, black coffee, plain tea and herbal tea.23
- No: anything with calories. Milk in your coffee, juice, sugar and smoothies all end the fast.2
- It depends: diet drinks and sweeteners have almost no calories, but some people find they make them hungrier. Try with and without.
How to start without struggling
Going straight to 16 hours is the main reason people give up in the first week. Build up instead:
- Week 1: 12:12. Stop eating after dinner and have breakfast 12 hours later. For many people that’s barely a change.
- Week 2: 14:10. Push breakfast back by two hours.
- Week 3: 16:8. Push it back two more, or finish dinner a bit earlier.
Hunger tends to come in waves, often around the times you used to eat, and then eases.4 A glass of water or a coffee helps.
Common mistakes
- Making up for it in the window. 16:8 works best when your meals stay normal-sized. In trials, eating in a shorter window didn’t lead to more weight loss than simply eating less.56
- Not drinking enough. A lot of what feels like hunger in the morning is thirst.
- Changing the times every day. Your body gets used to a rhythm. A different window every day makes it harder.
- Being too strict. A birthday dinner that runs late isn’t a failure. Start the next fast when you finish eating and carry on.
How Faaast helps with 16:8
Faaast is a free fasting tracker for iPhone, and 16:8 is its default. Tap Start fast when you finish eating, and each hour you get through fills a block on screen, so you always know how far you are and how far is left. It can remind you at the halfway point, when you reach 16 hours, and before your eating window closes. Each fast lands on a calendar, so you can see your streak build. There’s no account to make.
This guide is general information, not medical advice. Don’t fast without talking to a doctor if you’re pregnant or breastfeeding, under 18, have had an eating disorder, have diabetes, or take insulin or other medicine that lowers blood sugar.278
Questions
Does sleep count towards the 16 hours?
Yes. Any time you’re not eating counts, so most people do half their fast or more asleep.
Can I drink coffee during 16:8?
Yes, as long as it’s black. Calorie-free drinks like water and black coffee don’t break a fast. Milk, cream and sugar have calories, so they do.
Do I have to do 16:8 every day?
No. Many people fast every day because it’s easier to keep a routine, but some fast five days a week and eat normally at weekends. Pick what you can keep doing.
Will 16:8 help me lose weight?
It can help, because a shorter eating window often means eating less overall. But in trials, people who ate within 8 hours didn’t lose more than people who simply ate less, so what and how much you eat still matters most.
What if 16 hours is too hard?
Start with 12:12 or 14:10 and build up a couple of hours a week. Faaast has 12:12, 14:10, 16:8, 18:6, 20:4 and one meal a day, so you can move up when you’re ready.
Sources
- Saudi adults’ intermittent fasting practices, BMC Public Health, 2022. In this survey, 16:8 was the most practised pattern (43.8%). Smaller surveys elsewhere agree.
- 4 intermittent fasting side effects to watch out for, Harvard Health. Calorie-free drinks such as water and black coffee don’t break a fast; extra caution with diabetes and some medicines.
- What is intermittent fasting?, Cleveland Clinic (Love Your Heart podcast). A registered dietitian on coffee and tea during the fasting window.
- Natalucci et al., Spontaneous 24-h ghrelin secretion pattern in fasting subjects, Eur J Endocrinol, 2005. While fasting, the hunger hormone ghrelin still rises and falls around people’s usual mealtimes.
- Lowe et al., Effects of time-restricted eating on weight loss (TREAT trial), JAMA Intern Med, 2020. 12 weeks of 16:8 led to modest weight loss, not significantly different from three meals a day.
- Liu et al., Calorie restriction with or without time-restricted eating in weight loss, N Engl J Med, 2022. Over a year, an 8-hour window plus eating less was no better than eating less alone.
- Intermittent fasting, NHS (My Health London). Who shouldn’t fast: people with a history of eating disorders, and pregnant or breastfeeding women; people on medicine should talk to their GP practice first.
- Intermittent fasting: is the 5:2 diet good for weight loss?, British Heart Foundation. Who should avoid fasting: diabetes or low blood sugar, underweight, eating disorders, pregnancy or breastfeeding, children and teenagers.