Intermittent fasting, a trendy type of weight loss diet beloved by some celebrities, doesn’t extend lifespans, a major study suggests.
Instead eating less overall helped boost longevity experts found in a unique study on mice.
But slimmers looking to trim their love handles beware, it’s crucial not to lose weight while doing so as this could have the opposite effect, according to the results.
In an experiment on 1,000 mice unrelated mice US researchers set out to explore exactly how diets influenced lifespan.
The mice were unrelated, rather than the lab standard of closely related animals, in order to better mimic a human population.
Intermittent fasting, a trendy type of weight loss diet beloved by some celebrities, doesn’t actually extend lifespan, a major study suggests
Rodents were divided into five groups, one with unlimited food all the time, two where they were given 60 or 80 per cent of their regular feed, and two in where mice were given an unlimited amount of food but only on one or two days a week.
They were then studied for the rest of their lifespan.
Publishing their results in Nature, researchers found mice on the 60 per cent restricted diet lived the longest on average, about 34 months.
In human terms this is, very broadly, equivalent to a person being in their mid-80s.
Mice on 80 per cent diets lived the next longest, 30 months on average, equivalent to the early 80s in people.
In comparison rodents on the intermittent fasting diets only lived 28 months on average, roughly the mid-70s in human terms.
Animals given freedom to eat as much as they wanted as they wanted lived the least amount of time, 25 months on average, the equivalent of just reaching the 70s for a person.
This result meant that eating fewer calories had a greater impact on lifespan than fasting and this was true regardless of how fat or fit individual mice when the results were analysed on a mouse-by-mouse level.
And in a discovery that surprised the researchers it wasn’t weight-loss from eating fewer calories that seemed to have this effect.
In fact, it was the mice who lost the least weight despite their heavily restricted diet that tended to live the longest in the experiment.
In contrast those that did lose weight on these diets tended to have low energy and weakened immune and reproductive systems as well as shorter lives.
Professor Gary Churchill of Jackson Laboratory in New Jersey said: ‘Our study really points to the importance of resilience.’
He added: ‘The most robust animals keep their weight on even in the face of stress and caloric restriction, and they are the ones that live the longest.’
‘It also suggests that a more moderate level of calorie restriction might be the way to balance long-term health and lifespan.’
However, the researchers said another critical part of their study, and why they used genetically diverse mice for the experiment, is that there was huge variation in lifespan among all groups of mice.
For example, even among the mice on the calories restricted diets individual lifespans ranged from just a few months to four-and-a-half-years.
Analysing the mice further, researchers found genes that boosted resilience though helping maintain them body weight, body fat percentage and immune cell health during periods of stress that lived the longest.
The experts said this showed that although diet could be used to influence lifespan, at the end of the day an individual’s longevity could be at the mercy of genes.
Professor Churchill said: ‘If you want to live a long time, there are things you can control within your lifetime such as diet, but really what you want is a very old grandmother.’
Jennifer Aniston (left) and Nicole Kidman (right) are two starts previously linked to intermittent fasting
From the Kardashians to Prime Minister Rishi Sunak, it seems almost everyone has tried fasting. Proponents say the extreme dieting trend boosts energy levels and helps shed fat. Some opt for a 24-hour fasts, whilst others cram all their daily meals into a tight six-hour window in a bid to reap an array of claimed health benefits. But some studies have suggested skipping meals and delaying breakfast could also raise your risk of diabetes and even lead to a heart attack
This study was on mice and therefore is of limited application to people.
But Professor Churchill said the results had important implications for research on boosting lifespan in humans a field which typically looks at how the metabolism was function as measure of biological age.
‘While caloric restriction is generally good for lifespan, our data show that losing weight on caloric restriction is actually bad for lifespan,’ he said.
‘So when we look at human trials of longevity drugs and see that people are losing weight and have better metabolic profiles, it turns out that might not be a good marker of their future lifespan at all.’
Several famous faces have used or reportedly used intermittent fasting over the years.
Actors Mark Wahlberg (left) and Chris Pratt (right) have also used intermittent fasting to slim down for their roles
Benedict Cumberbatch and former PM Rishi Sunak have also been linked to the diet in the past
Kourtney Kardashian is also among the A-listers to have jumped on the fasting trend since it shot to prominence in the early 2010s. Here she is pictured earlier this year
These include the likes of Jennifer Aniston, Benedict Cumberbatch, Kourtney Kardashian and Nicole Kidman.
In October 2019, Aniston said she doesn’t eat breakfast and only starts eating after midday.
Mark Wahlberg is also a fan of intermittent fasting, famously not eating his first meal until 12pm. He stops eating by 6pm.
Actor Chris Pratt also credits intermittent fasting for helping him lose 60lbs (27kg) for action star roles.
It isn’t just the Hollywood elite, ex-Prime Minister Rishi Sunak also got on board the trend, stating in 2022 ‘I do intermittent fasting, so on most days I have nothing for breakfast.’
However, some studies have found such diets could raise your risk of diabetes and even lead to a heart attack.
