Before you choose a fasting schedule, it helps to know what it actually does in studies. Most of the weight people lose on these plans comes from eating less overall, not from the hours without food, so the best version is the one that fits your days and that you can keep up for months. Below are the main methods, what the strongest trials found, and who should leave fasting alone.
What is intermittent fasting?
Intermittent fasting is a way of timing your meals rather than a list of foods to eat or avoid. You switch between periods of normal eating and periods of eating very little or nothing. Three patterns account for most of the research:
| Method | How it works | Example used in studies |
|---|---|---|
| Time-restricted eating | All food is eaten inside a daily window, often 6–8 hours long | Eating between noon and 8 p.m., then fasting overnight and through the morning |
| 5:2 | Two days a week of very low intake, usual eating on the other five | 500–600 calories on two mostly non-consecutive days |
| Alternate-day fasting | Fast days alternate with days of unrestricted eating | Water only, or 500–600 calories, every other day |
The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) describes time-restricted eating as the most researched type. The 5:2 example comes from a 12-month trial in adults with type 2 diabetes published in JAMA Network Open.
Does intermittent fasting help you lose more weight than cutting calories?
Not according to the best evidence so far. A 2026 Cochrane review pooled 22 randomised trials with 1,995 adults living with overweight or obesity, each followed for at least six months. Compared with regular dietary advice, it concluded that intermittent fasting "may result in little to no difference in weight loss or quality of life."
A 2025 analysis in The BMJ combined 99 randomised trials with 6,582 adults. Every fasting plan, and ordinary daily calorie reduction, led to weight loss compared with eating freely. Alternate-day fasting was the only method that beat daily calorie reduction, and only by about 1.3 kg on average. In the 17 trials that lasted 24 weeks or longer, the diets only stood apart from unrestricted eating, not from one another.
Head-to-head trials point the same way:
| Trial | What was compared | Result |
|---|---|---|
| New England Journal of Medicine, 2022: 139 adults with obesity, 12 months | A daily calorie target plus an 8 a.m. to 4 p.m. eating window, against the same calorie target alone | 8.0 kg lost with the window and 6.3 kg without it; the difference was not statistically significant |
| JAMA Internal Medicine, 2020: 116 adults with overweight or obesity, 12 weeks | Eating only between noon and 8 p.m., against three structured meals a day | About 0.9 kg lost against 0.7 kg, with no significant difference between groups |
| JAMA Internal Medicine, 2017: 100 adults with obesity, 12 months | Alternate-day fasting, against eating 75% of energy needs every day | Similar weight loss, but 38% dropped out of the fasting group against 29% of the daily calorie group |
Why does fasting lead to weight loss at all?
Mostly because people eat less. In an NIDDK interview, a researcher who runs fasting trials explained that people on time-restricted eating tend to cut about 500 calories a day without counting, and that in her 12-month trial both time-restricted eating and calorie counting led to about 5% weight loss. She did not see fasting as better than other approaches, but as an option for people who are tired of tracking what they eat.
Timing on its own does less than many people expect. In the 2020 trial above, estimated calorie intake was similar in both groups, and so was weight loss. The time-restricted group also lost more lean mass than the comparison group, which is one reason to make sure your meals carry enough protein (see how much protein you need).
Does intermittent fasting improve blood sugar, cholesterol or blood pressure?
So far, fasting does not seem to improve these markers more than other ways of eating less:
- Blood sugar. The BMJ analysis found no difference in HbA1c, a longer-term blood sugar measure, between fasting, daily calorie reduction and unrestricted diets. In the type 2 diabetes trial, HbA1c fell by 0.3% with the 5:2 approach and 0.5% with daily calorie reduction, a gap small enough for the two to count as equivalent by the researchers' own standard.
- Cholesterol. HDL cholesterol did not differ between approaches in the BMJ analysis. In the 12-month alternate-day trial, LDL cholesterol rose more in the fasting group than in the daily calorie group.
- Blood pressure and other risk factors. In the 2022 eating window trial, blood pressure, waist size and metabolic risk factors showed no meaningful difference between the two groups.
In short, fasting is one way to cut back, not a shortcut to better numbers.
How can you make intermittent fasting easier to stick with?
If you decide to try it, these habits keep it practical:
- Choose a window that fits your life. A schedule that clashes with family meals, shift work or training is hard to keep. A modest window you can hold is more useful than an ambitious one you give up on.
- Plan the food, not just the hours. In the alternate-day trial, people tended to eat more than planned on fast days and less than planned on the other days, so the intended pattern drifted. The meal plan builder sets out a week of balanced meals that you can fit inside your eating window.
- Build balanced plates. Half vegetables and fruit, a quarter protein and a quarter whole grains is a simple pattern to follow; the anti-inflammatory plate shows how.
- Keep the whole day in view. Since the benefit comes from eating less, a large catch-up meal can cancel it out. How many calories you need explains how to estimate a sensible daily amount.
- Check in after a few weeks. If fasting leaves you preoccupied with food, prone to overeating, or tired and irritable, there is no need to push through. Daily calorie reduction gave similar results in the trials above.
Who should not try intermittent fasting?
Fasting is not suitable for everyone. Skip it, or only try it with your doctor's guidance, if any of these apply to you:
- You are pregnant or breastfeeding. An NHS guide says pregnant or breastfeeding women should not attempt intermittent fasting, and the NIDDK notes that fasting has not yet been studied in pregnancy.
- You have had an eating disorder. The NHS guide advises people with a history of eating disorders such as anorexia or bulimia not to fast, and the researcher interviewed by the NIDDK said people with that history should not follow fasting plans.
- You take insulin or other diabetes medicines that can cause low blood sugar. In the type 2 diabetes trial, these medicines were reduced from the start, and the rules were tightened during the study mainly because of low blood sugar. Even so, 8 of the 46 people taking sulfonylureas or insulin had low blood sugar, 6 of them in the 5:2 group. The NIDDK says people with diabetes need to work closely with their doctor to adjust these medicines.
- You are under 18. The trials in this article enrolled adults, and children and teenagers are still growing. A concern about a young person's weight is best taken to their doctor.
- You have another long-term condition or take regular medication. The NHS guide asks people on medication to tell their healthcare team before changing their diet.
When should you talk to a doctor about fasting?
Talk to a doctor or registered dietitian before you start if any point in the list above applies to you. The same goes for older adults: the NIDDK researcher raised a concern about losing too much muscle in this group. Once you have started, stop fasting and get medical advice if you feel faint, dizzy, shaky or confused, especially if you take medicine for diabetes. It is also worth speaking to a professional if fasting starts to bring on binge eating, guilt about food or a fear of eating outside your window.
To turn this into a plan, start with the meal plan builder. The full guide to nutrition shows how calories, protein and balanced plates fit together.
