Eating style
Intermittent fasting
Eating within set hours or on set days. The main patterns, what reviews found against ordinary calorie restriction, and who should not try it.
The main patterns
Intermittent fasting is an umbrella term. Time-restricted eating keeps all meals inside a daily window, often about eight hours, and is the gentlest version. Alternate-day fasting and the 5:2 pattern instead cut intake sharply on some days and eat normally on the others. None of them says what to eat, so food quality and total calories still matter.
This guide concentrates on time-restricted eating. Patterns built on fast days depend on very low calorie intakes on those days, and we do not publish targets that low. If one of those appeals to you, set it up with your doctor or a registered dietitian who can check that it suits you.
What the evidence shows
A 2026 Cochrane review of 22 trials with 1,995 adults found that intermittent fasting may make little to no difference to weight loss compared with regular dietary advice. Compared with no intervention, people lost about 3% more of their body weight. A 2025 BMJ analysis of 99 trials reached a similar verdict: fasting and continuous calorie restriction both work, about equally.
So the benefit appears to come from eating less, not from the clock. The BMJ analysis found a small extra loss with alternate-day fasting, about 1.3 kg, but only in shorter trials; in those lasting 24 weeks or more, fasting did no better than ordinary dieting. Choose it if a shorter eating day is easier for you to keep to.
Doing it sensibly
Keep your usual calorie and protein targets and fit them into the window; the planner works the same way with two or three meals. Proper meals with enough protein tend to be easier than grazing through the window. If the pattern leaves you overeating when the window opens, light-headed or preoccupied with food, widen it or stop.
Worth knowing
- If you have, or have had, an eating disorder or disordered eating, do not use fasting: rules about when you may eat can reinforce restriction. Speak to your care team.
- If you take insulin, a sulphonylurea or other glucose-lowering medication, fasting raises the risk of hypoglycaemia. Do not start without your diabetes team, who may need to adjust doses and monitor you.
- Not for under-18s, during pregnancy or breastfeeding, or if you take medicines that must be taken with food.
Common questions
Is intermittent fasting better than counting calories?
Not on average. Reviews of randomised trials find similar weight loss from fasting patterns and from ordinary daily calorie restriction. The better choice is whichever you can keep to.
Does it matter which hours I choose?
Evidence on timing is preliminary. Some small studies favour eating earlier in the day, but the American Diabetes Association describes this research as not yet conclusive. Pick hours you can live with.
Sources
- Garegnani et al., Cochrane Database of Systematic Reviews (2026): Intermittent fasting for adults with overweight or obesity
- Semnani-Azad et al., BMJ (2025): Intermittent fasting strategies and cardiometabolic risk factors, systematic review and network meta-analysis
- American Diabetes Association, Standards of Care in Diabetes 2026: Section 5, Facilitating Positive Health Behaviors and Well-being
- Harvard T.H. Chan School of Public Health: Diet Review, Intermittent Fasting for Weight Loss
General information, not medical or dietary advice. Speak to a doctor or registered dietitian about your own situation.