How do you do 16:8 fasting?
Pick an 8-hour window, like 10am to 6pm. Then fast for the other 16 hours, with water, tea or coffee. But in trials, the clock alone barely moved weight. One thing did.
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How does 16:8 intermittent fasting work?
You eat all your meals and snacks within 8 hours. For the other 16, you have drinks but no food. Diabetes UK gives 9am to 5pm or 10am to 6pm as examples.
Most of the 16 hours pass while you sleep. Finish dinner at 6pm and your next meal is at 10am.
| Eat between | Fast between | Who used it |
|---|---|---|
| 8am and 4pm | 4pm and 8am | A 12-month trial in China |
| 9am and 5pm | 5pm and 9am | Diabetes UK example |
| 10am and 6pm | 6pm and 10am | Diabetes UK example |
| 12pm and 8pm | 8pm and 12pm | A 12-week trial in the US |
Sources: Diabetes UK; Lowe 2020; Liu 2022
A later window keeps dinner with family. An earlier one means no evening snacks.
Pick the window that fits your week, and keep it the same each day.
Does 16:8 fasting help you lose weight?
Only if you end up eating less. NICE says a weight loss diet must keep the calories you eat below the calories you use.
| Trial | What people did | Weight change |
|---|---|---|
| 12 weeks, 116 US adults | 16:8 (12pm to 8pm) eating freely, or 3 meals a day | 16:8 down 0.94 kg. 3 meals down 0.68 kg. No real gap. |
| 12 months, 139 adults with obesity | Everyone cut calories. Half also ate only from 8am to 4pm | 8-hour window down 8.0 kg. Calorie cut only down 6.3 kg. The gap could be chance. |
That one thing is eating less. In the 12-month trial, both groups cut calories, and both lost 6 to 8 kg.
So 16:8 is a tool, not a trick. Diabetes UK says people tend to eat fewer calories when they only eat in set hours. That’s how it can help.
In the 12-week trial, 50 people were measured in clinic. Among them, the 16:8 group lost more lean mass from their arms and legs. Lean mass includes muscle.
See keeping muscle while you lose weight and protein for weight loss.
Prefer 2 low-calorie days a week instead? See the 5:2 in our best diet to lose weight guide.
What can you drink during a 16 hour fast?
Water, tea, coffee and sugar-free squash, at any time. Diabetes UK lists only non-alcoholic drinks for the fasting hours, so save any alcohol for your eating window.
Food is out. For 16:8, Diabetes UK says to avoid solid food in those hours. Diabetes UK says to drink plenty in those hours so you stay hydrated.
Hungry at first? People often feel hungry and get cravings, though for some this eases over time. Keep a hot drink to hand for the hardest hour.
Is 16:8 fasting safe?
It isn’t for everyone. NICE makes no recommendation on intermittent fasting yet. It has asked for more research instead.
| If you are | What the advice says |
|---|---|
| Pregnant or breastfeeding | Don’t do intermittent fasting. |
| A teenager | Not right for teenagers. |
| Underweight, or have had an eating disorder | Only with a health professional’s support. |
| Taking medicine for diabetes | Talk to your doctor or diabetes team first. Some medicines can make blood sugar drop too low. |
| Having treatment for cancer | Speak to your medical team before trying fasting. |
Sources: Dietitians Australia; Diabetes UK
Hunger is the main side effect. You may also feel weak or less sharp, which may pass as your body adapts.
Saw headlines that eating within less than 8 hours a day almost doubles the risk of dying from heart and circulatory disease? The BHF says that 2024 study was not peer-reviewed and only asked about 2 days of eating. It shows a link, not a cause.
Never stop or change a prescribed medicine without your prescriber.
How to start 16:8 fasting
Ease in. Dietitians Australia calls 12 hours of fasting and 12 of eating the simplest way to start.
How to start 16:8 this week
- Cut out night-time snacks first, then try a 12-hour fast, such as 7pm to 7am, and stretch it towards 16.
- Fill your eating window with wholegrains, fruit and veg, beans and pulses.
- Don’t make up for the fast by eating more in your window.
- Drink plenty of water, tea or other non-alcoholic drinks while you fast.
- If side effects carry on and get in the way of your day, stop and get advice.
- Skip 16:8 if you are pregnant, breastfeeding or a teenager. If you are underweight or have had an eating disorder, only try it with a health professional’s support.
Sources: Dietitians Australia; Diabetes UK
Need meals for your window? See the weight loss meal plan.
Have diabetes? See the type 2 diabetes food list.
When to speak to a GP
Book an appointment if:
- You take insulin or other diabetes medicine and want to try 16:8. Talk to your healthcare team first.
- You eat very little, have very strict food habits, make yourself sick, take laxatives, exercise too much or worry a lot about your weight and shape. The NHS says see a GP as soon as you can.
- Along with those habits, you feel cold, tired or dizzy, get tingling or numbness in your arms and legs, your heart races, you feel faint, or your periods stop.
- Side effects of fasting carry on and get in the way of your day.
Worried about your eating? You can also call the Beat helpline on 0808 801 0677.