Such diets focus on when you eat, rather than what you eat, with regular periods of fasting thought to reset and rebalance the body – making you not only slimmer but sharper and more energetic.
Dr Cole is causing a stir thanks to glowing endorsements from super slim Paltrow, 48, who calls his book “doable and exhilarating” – but fasting diets like his are proving to work particularly well for men, especially those of a certain age.
Prime Minister Boris Johnson has shed two stone in the last year, thanks, in part, to fasting. His personal trainer, Harry Jameson, is an advocate of the 16:8 diet, where followers only have eight hours each day to consume their daily allowance of calories. Johnson reportedly skips breakfast or lunch as part of his new regimen – which is being combined with a vigorous fitness schedule.
He may have less to lose, but Rishi Sunak, the Chancellor, is also a fan of intermittent fasting, with his slim physique thought to be down to the 5:2 diet – which his predecessor, George Osborne, followed to shed the pounds, along with stars such Benedict Cumberbatch, the actor, and Phillip Schofield, the TV presenter. On fasting days, teetotal Sunak reportedly survives on Granny Smith apples and a pile of cashew nuts.
Popularised by Dr Michael Mosley in his book The Fast Diet, the 5:2 allows you to eat as normal for five days of the week but fast on the other two, limiting your calorie intake to around 800 a day.
Recently, Mosley has also promoted The Fast 800, a new 12-week schedule that involves cutting your calories to a limit of 800 per day for the first two weeks before reverting to the 5:2 plan. The benefits, explains Dr Mosley, go beyond just shedding the pounds.
“You should not only see rapid weight loss but big improvements in blood sugars and blood pressure too,” he says.
With no foods off limits, and the ability to adjust it around your own schedule, fasting’s appeal lies in its simplicity. For men, it represents a challenge to be taken on which can feel more socially acceptable than saying you’re “going on a diet”.
“A lot of men tell me they find intermittent fasting easier than conventional diets because it is very simple and straightforward,” says Dr Mosley. “It also fits into most busy lifestyles.”
He adds that men tend to see results more quickly than women on fasting diets, especially in terms of weight loss.
“As men possess more muscle, on average, than women, they are likely to lose weight more rapidly. Incorporating some resistance exercise into your fasting routine, such as squats or press-ups, can also help to maximise your results.”
A large body of evidence shows that fasting diets are more effective than conventional daily calorie reduction for weight loss and improved blood sugar markers.
But its macho image is also bolstered by claims that fasting has benefits for the brain and improves performance at work, hence its popularity among the “tech bros” of Silicon Valley. Devotees such as Jack Dorsey, the tech entrepreneur who co-founded Twitter, say it makes them sharper and more productive, in part because you’re no longer distracted by thinking about the next meal.
The effect is thought to be down to autophagy – a process that kicks in when your body has been without food for 12 hours or more, whereby old or damaged cells are cleared away to make way for new ones. Research by Professor Mark Mattson, at the National Institute of Health, has shown reducing your calorie intake for two days a week can help to boost levels of brain-derived neurotrophic factor, a hormone that acts like a fertiliser on brain cells, helping to encourage not just survival but growth too.
“Fasting allows your body time to do a bit of spring cleaning and switch on those important repair mechanisms,” says Dr Mosley.
“I think that is one reason why many people say that fasting makes them feel sharper, smarter and also surprisingly more cheerful. I certainly find that.”
The holy grail of weight loss is a diet that works in the long term, and there is hope that fasting plans really do bring sustainable results. In 2019, Professor Roy Taylor, of Newcastle University, conducted a study with 298 diabetic patients randomly allocated to a rapid weight loss programme of around 800 calories a day, for up to 20 weeks.
Two years later, he returned to the group and found those who had been on the weight loss plan were, on average, 16.5lb (7.5kg ) lighter than at the start of the study and were on half of the amount of drugs as the rest of the control group. A third, meanwhile, now had normal blood sugar levels, despite being off all medication. In short, the weight stayed off and some even put their diabetes into remission.
That might come down to the fact abstinence has the effect of making us learn what hunger truly feels like, and to distinguish those signals from “emotional eating”, and the urge to snack. It’s a way to reset your relationship with food while giving your digestive system a much-needed break.
“You are not supposed to be eating 24 hours a day,” says Jason Fung, author of The Obesity Code. “During feeding you store energy and during fasting, you burn it. If you are always feeding, you can’t burn body fat. As such, fasting should be done every day – something like 10-14 hours (after dinner until breakfast).”
Indeed, while previous fasting programmes such as the 5:2 or 16:8 offer structured windows of time for eating and fasting, Dr Cole’s “intuitive fasting” is about being guided by the body, eating when your body tells you to and ignoring set meal times and patterns, ensuring you build in periods of fasting.
“Many of us have never paused to ask ourselves questions like: do I eat because my brain tells me to – or because my body is really, truly hungry?” he writes.
“What and when we eat has become so ingrained in our culture and lifestyle that many of us have never stopped and asked ourselves if the way we eat is working for us.”
Intuitive Fasting by Will Cole (RRP £22.50). Buy now for £18.50 at books.telegraph.co.uk or call 0844 871 1514