Intermittent Fasting for Weight Loss in 2026: Cochrane Pooled 22 Trials and 1,995 Adults – and Found It Beat Ordinary Dieting by Nothing
“Intermittent fasting just doesn’t seem to work for overweight or obese adults trying to lose weight.” That’s the lead author of a Cochrane review published in February, and it’s about as blunt as a systematic review gets.
In This Article
- Intermittent fasting for weight loss: what Cochrane actually counted
- "No better than dieting" is not the same as "no use"
- The 16:8 question
- Who shouldn't be fasting at all
- What a fast day does to the rest of your week
- What 2 to 5% looks like on the scales
- What the trials can't see
- If it's already working for you
- What I'd do before the Christmas diet season starts
Luis Garegnani and his colleagues pooled 22 randomised trials involving 1,995 adults. They found no clinically meaningful difference in weight loss between intermittent fasting and ordinary dietary advice. Garegnani added that online enthusiasm “may be running ahead of the data.”
So why is half of Britain still skipping breakfast?
I think the honest answer is that the headline is only half the story, and the half that gets left out is more useful than the half that gets shared. Intermittent fasting for weight loss isn’t a scam, and it isn’t a shortcut either. It’s a way of dieting. Whether it’s the right way for you depends on a few things the trials can’t tell you.
Intermittent fasting for weight loss: what Cochrane actually counted
The review, published in the Cochrane Database of Systematic Reviews on 18 February 2026, covered three styles of fasting: alternate-day fasting, periodic fasting (the 5:2 pattern sits here) and time-restricted eating, where you squeeze all your food into a set window each day. The participants came from North America, Europe, China, Australia and South America. The outcomes were mostly measured at six to twelve months.
The conclusion, in the review’s own subtitle as reported by the Science Media Centre, was that intermittent fasting “did not appear to have a clinically meaningful effect on weight loss compared to standard dietary advice or doing nothing.” You can read the UK expert reactions on the Science Media Centre site.
The comparison with doing nothing is where it gets muddy. The commentary describes a 2 to 5% average drop in body weight at six to twelve months for people who fasted, which is statistically real and, on a 90kg person, somewhere between 1.8kg and 4.5kg. The reviewers still judged that not clinically meaningful. Whether you’d agree depends on how much you were hoping for. I wouldn’t call 4kg nothing, but I wouldn’t call it the transformation the books promised either.
The authors also called the evidence “very uncertain”. Many trials were small, reporting was uneven, and side effects weren’t consistently recorded across studies.
“No better than dieting” is not the same as “no use”
This is where I part company with some of the louder reactions.
Dr Baptiste Leurent at UCL said the review found “absolutely no benefit of intermittent fasting on weight loss, when compared to standard dietary advice.” That’s a fair reading of the comparison. But read it again: the comparison group was people being given standard dietary advice, which is itself a form of dieting that works modestly well. Fasting matched it. Dr Adam Collins at the University of Surrey was more careful, saying the headline finding “should, I feel, be interpreted with a little caution”.
What the review didn’t find is that fasting is worse. The British Heart Foundation, summarising a BMJ review, puts it this way: all three types of intermittent fasting and the continuous low-calorie diet “lead to a small amount of weight loss compared to eating normally.” Same ballpark, same modest result.
And that points at something I’d argue the debate misses. Most diets don’t fail because the arithmetic is wrong. They fail because people can’t keep doing them. If a rule like “nothing after 8pm” or “two lighter days a week” is simpler for you than counting calories every day, then matching the performance of standard advice isn’t a disappointment. It’s the whole point.
The flip side is that if you hate being hungry, you’ll hate this, and no trial result will change that.
The 16:8 question
Time-restricted eating is the version most people actually try, because it asks the least of you. Eat between, say, 10am and 6pm, fast the rest.
The Cochrane review lumped it in with the other two types, and I haven’t been able to find a clean, separate weight-loss figure for it from that review, so I won’t invent one. A separate network meta-analysis of time-restricted eating has looked at how the timing and length of the eating window affect metabolic outcomes, which you can find on PubMed Central, though I’d read it as a research pointer, not a verdict.
What I can say is that there’s no sign in the current evidence that eating earlier in the day, or squeezing the window tighter, is a magic setting. The plausible mechanism is dull: shorter windows tend to mean fewer snacks, fewer drinks and less late-night grazing. Fewer calories in, same as always.
If you’ve tried it and lost weight, that’s probably why. It doesn’t need a special explanation.
Who shouldn’t be fasting at all
The weight-loss debate gets all the attention, but the safety question deserves more.
The BHF’s guidance on the 5:2 diet is clear that it isn’t suitable if you have diabetes or experience low blood sugar, if you’re underweight, if you have a history of eating disorders, if you’re pregnant or breastfeeding, or if you’re a child or teenager. It also suggests checking with your doctor first if you have any health condition or take medicines with food. It points out that none of the trials in the BMJ review it relied on lasted longer than a year, so long-term effects are an open question.
Diabetes is the one I’d underline. Know Diabetes, a UK diabetes education site, warns that if you’re on insulin or on medication such as sulphonylureas or glinides, an intermittent fasting plan “could significantly increase the risk of hypos”, and says to tell your diabetes healthcare team at your GP practice before changing your diet so they can adjust your medication. That’s not a minor footnote. It’s the difference between a diet and an emergency.
Eating disorders are the other one. A rule-based pattern that rewards going without food can be a hard thing to switch off for someone with that history, and the BHF’s list says as much. If that’s you, skip it.
What a fast day does to the rest of your week
The BHF notes that some people feel more hungry, tired or irritable on fast days. Those are the polite words for it. In practice, a very low-calorie day can bleed into the days either side: you’re flat on the day, hungry the next, and quite possibly less active throughout.
That last part matters more than it sounds. If fasting leaves you sitting down more, you’ve handed back a chunk of whatever deficit you built. We looked recently at how many steps a day are worth aiming for, and it’s worth keeping that number in mind on a fast day.
Then there’s protein. Dieting of any kind risks losing muscle along with fat, and a fasting pattern that crams eating into a short window can make it harder to spread protein across the day. Our piece on how much protein you actually need is a better guide to that than a fasting app, and the same applies to fibre, which tends to be the first thing to drop out of a restricted diet – see the fibremaxxing piece.
Alcohol is the sneaky one. A drink on a “free” day can undo most of a fast day’s saving, and our Sober September piece is the place to start if you’re thinking about cutting back.
What 2 to 5% looks like on the scales
Percentages hide how small or large a change feels, so here’s the arithmetic. At 70kg, a 2 to 5% drop is 1.4kg to 3.5kg. At 90kg it’s 1.8kg to 4.5kg. At 110kg it’s 2.2kg to 5.5kg. Those are averages across people, remember, so plenty of individuals will have done better and plenty worse.
Is that worth the effort? For someone with a lot to lose, a few kilos is a start, not a finish line. For someone hoping to drop a dress size before a wedding, it’s a disappointment. The Cochrane reviewers weren’t saying that nobody loses weight while fasting. They were saying that, on average, the people who fasted weren’t doing better than people following ordinary advice, and that the gain over doing nothing was modest.
I’d add one more point of my own. The review looked at adults with overweight or obesity. If you’re already a healthy weight and fasting for some other reason, this particular evidence doesn’t speak to you at all.
What the trials can’t see
A trial that runs for six to twelve months can tell you a lot about the first year. It can’t tell you what happens in year three, when the novelty has gone and the pattern has to survive a holiday, a house move, a new job and a family wedding. The BHF made the same point about the 5:2 evidence: nothing it reviewed ran for longer than a year.
Trials also struggle with the messy human stuff. People drop out. They fudge the rules. They report what they ate on the days they remember to. None of that is a flaw in this specific review, since it affects nearly all diet research, but it’s a reason to treat any single average with a pinch of salt.
And there’s the question nobody can answer from a spreadsheet: which version of you is reading this? A shift worker, a parent who eats whatever’s left on the kids’ plates at 6pm, someone who trains first thing in the morning on an empty stomach – the same rule lands very differently on each of them. I’d trust the pattern that fits your actual week over the one with the better headline.
If it’s already working for you
Then carry on. I mean that.
I’m not going to tell someone who’s lost a stone on 16:8 and feels fine that the Cochrane review means they’ve been fooling themselves. A review of averages can’t overrule a specific person’s result. If the pattern is simple, you’re eating enough protein and you’re not white-knuckling it, you’ve found a rule you can keep, and that’s most of the battle with any diet.
What I’d drop is the idea that the clock is doing something mystical. If you move your window and nothing changes, that’s what the trials would predict.
The BHF, incidentally, suggests the Mediterranean diet may be easier to stick with long term than fasting patterns. It’s not a dramatic claim, but it’s one worth testing against your own tolerance for hunger.
If you’re curious about how your body actually responds to meals, rather than guessing, we looked at whether continuous glucose monitors are worth the money. Read that before you spend a penny.
What I’d do before the Christmas diet season starts
There’s a predictable surge in diet advice from now until January, and intermittent fasting will be at the front of it. Here’s the order I’d work through.
First, rule yourself in or out. If you have diabetes, take medication with food, are pregnant or breastfeeding, are underweight, or have ever had an eating disorder, speak to your GP before trying any fasting pattern. Second, pick the gentlest version. A time-restricted window of about ten hours is a lot easier to live with than alternate-day fasting, and nothing I’ve found shows the harsher versions work better. Third, set a review point: eight to twelve weeks, a weigh-in, and an honest look at your energy, mood and sleep. And fourth, if it isn’t working, stop without guilt. The trials say it’s one dieting method among several, not a test of character.
My verdict: intermittent fasting for weight loss is neither the revolution the books sold nor the dud the headlines suggest. It’s a perfectly reasonable rule for the people who find it easy to follow, and an unnecessary misery for everyone else.
So what happened when you tried it – did the weight come off, or did the rule only last as long as your willpower did?
