How do you do 12 hour fasting?
Stop eating at 7pm and wait until 7am. For 14:10, wait until 9am. But the clock on its own won’t shift your weight. One habit decides that.
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What is 12 hour fasting?
You fast for 12 hours and eat in the other 12. It’s also called 12:12. Dietitians Australia calls it the simplest method: last meal at 7pm, next meal at 7am.
You sleep through most of it. If you go to bed at 11pm and wake at 7am, only 4 hours of the fast are awake hours.
| Plan | No food between | Eat between |
|---|---|---|
| 12:12 | 7pm and 7am | 7am and 7pm |
| 14:10 | 7pm and 9am | 9am and 7pm |
| 16:8 | 8pm and 12pm | 12pm and 8pm |
Source: Dietitians Australia
In the fasting hours you can drink water, tea, coffee and sugar-free squash. Diabetes UK lists only non-alcoholic drinks, and says you can have them at any time.
Pick a finish time you can keep most nights. Tonight, make that your kitchen closing time.
What is 14:10 intermittent fasting?
You fast for 14 hours and eat within 10. Finish at 7pm, then have breakfast at 9am.
That can be a bigger change than it sounds. In one US study of healthy adults, half ate across more than 14.75 hours a day. Count from your last bite at night to your first in the morning.
One 3-month trial tested an 8 to 10 hour eating window in 108 adults with metabolic syndrome. A group of health problems linked to diabetes and heart disease. Their usual window was about 14 hours.
Compared with usual care alone, the shorter window lowered HbA1c by 0.10%. HbA1c is a blood sugar test. The authors called the gain modest, and there were no major side effects.
So treat 14:10 as the next step once 12 hours feels easy.
Does 12:12 or 14:10 fasting help you lose weight?
Only if it helps you eat less. That’s the one habit that decides it.
Dietitians Australia says fasting works for weight loss simply because you eat less food. Most trials find only small differences between fasting and other ways of eating less.
NICE says weight loss diets for adults should keep the calories you eat below the calories you use. Closing the kitchen at 7pm can help, if it cuts out evening snacks you would have eaten.
It won’t help if you eat the same food, just earlier. Check your numbers with the calorie deficit calculator.
Most weight loss methods, fasting included, often bring short-term loss and then regain. Choose a window you could keep for years, not weeks.
For longer fasts and what trials found, see 16:8 fasting and intermittent fasting for weight loss.
Is 12 hour fasting safe?
It isn’t right for everyone. NICE has no recommendation on intermittent fasting yet and has asked for more research.
| 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 problems with eating in the past | Only if a health professional is keeping an eye on you. |
| 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 you try fasting. |
Sources: Dietitians Australia; Diabetes UK
Hunger is the main side effect. You may also feel weak or less sharp, which may only last while your body adapts.
Never stop or change a prescribed medicine without your prescriber.
How to start 12 hour fasting
Start small. Dietitians Australia suggests cutting out night-time snacks as one way to begin.
From no late snacks to 14:10, one step at a time
- 1
Stop night snacks
Nothing to eat after dinner. Drinks are fine.
- 2
Fast 12 hours
No food from 7pm to 7am.
- 3
Try 14:10
Push breakfast to 9am once 12 hours feels easy.
- 4
Keep what suits you
No one way is best. Change it if you need to.
Source: Dietitians Australia
How to start 12 hour fasting this week
- Cut out night-time snacks, then fast 12 hours, such as 7pm to 7am.
- When that feels easy, try 14:10 by moving breakfast to 9am.
- Break your fast with veg, fruit, wholegrains and lean protein.
- 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 from a health professional.
Sources: Dietitians Australia; Diabetes UK
Hungry in the evening at first? Diabetes UK says hunger and cravings can ease over time for some people. A hot drink can fill the gap.
Ready for a longer fast later? See 18:6 fasting.
When to speak to a GP
Book an appointment if:
- You take insulin or other diabetes medicine and want to try fasting. 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, your mood changes (you feel withdrawn, anxious or low), you feel cold, tired or dizzy, get pain, tingling or numbness in your arms and legs, your heart races, you faint or feel faint, you get bloating, constipation or diarrhoea, your weight is very high or very low for your age and height, 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.