Fasting is very much in vogue as a weight loss tool. It has also been a religious staple for thousands of years - so what tips do priests have for contemporary fasters?
Fasting is not a fad - it's been going on for millennia in nearly all the major faiths. Today it's increasingly directed not at spiritual enlightenment but shedding the pounds.
A growing body of evidence suggests that diets such as the 5:2, which restricts calories on two days of the week, can be a healthy way to lose weight.
It's no cake-walk, however - temptation is everywhere.
So what advice do monks and priests who regularly go without food have for the secular faster?
Father Alexander da Costa Fernandes, a Catholic monk at Worth Abbey, West Sussex, has been fasting for 20 years, usually on Wednesdays and Fridays, drinking just water and the odd cup of coffee.
It was tough at the start and he'd get headaches. It took him nine months to fast seriously.
The trick, he says, is to gradually get used to the idea of fasting. The body "craves what it expects".
He advises starting by giving up breakfast or your mid-morning biscuits to ease yourself in. When you've mastered that, then give up something else. A bread-and-water-only diet is a sensible approach, he says.
Drinking a lot of liquids is crucial, Father Alexander adds. It helps create the illusion that you have a full stomach.
Fasting means different things to different people.
An absolute fast, practised by Jews for about 24 hours at Yom Kippur and Tisha B'Av, forbids both eating and drinking.
During Ramadan, the ninth month of the Islamic calendar, Muslims abstain from food or water during daylight hours. Fasting is important to Hindus and some Buddhist monks and nuns forsake evening meals.
In the secular world, the 5:2 diet defines fasting as a daily calorie intake of 500 for a woman and 600 for a man, on two non-consecutive days a week.
Such a diet isn't for everyone, and the approach has its critics. The NHS says more research needs to be done on intermittent fasting diets and advises people to consult their GP before embarking on one.
Fasting is not just physically demanding. It's also psychologically tough, says the Anglican Bishop of Manchester, the Right Reverend David Walker, who has drunk only tea and water one day a week during lent for the last decade.
"The night before you start, you think: 'How am I going to get through the day?'" says Bishop Walker. But it's never as bad as you expect, he adds.
The key thing is to make sure you're busy at normal mealtimes, he says. The body is conditioned to want food according to a routine.
To take your mind off hunger, Bishop Walker suggests doing something you're engrossed by - a favourite programme on television, a Sudoku puzzle - when you'd normally be sitting down to breakfast, lunch or dinner.
As for coping without food, any fit and healthy person should be able to manage a short fast, according to Father Alexander. His longest stretch is five days. "There's a lot of hype around food," he says.
People are bombarded by messages about the need for energy and vitamins, he says. "What my five-day fast taught me is we carry so much energy in our own bodies as fat and you only start to use it up after a few days."
Hunger pangs are inevitable even for old hands. Especially when there's freshly baked bread or a bacon sandwich in the vicinity.
So what should you do?
Learn to discipline the mind, says Father Alexander. "If on a fast day you're thinking about chocolate cake, or having scampi tonight, then it's totally unhelpful."
Push the thought gently away and instead concentrate on something you should be doing, he says.
Doing something as "part of a community" makes fasting less onerous, says Bishop Walker. So do it with friends or colleagues - you won't feel so isolated when the going gets tough.
All these techniques are helpful. But for religious people, feeling hungry is part of the point.
"Sometimes feelings of hunger are helpful from a spiritual point of view," Bishop Walker says.
"When I have a pang of hunger it reminds me that I'm fasting for a religious purpose. It turns my mind to God becoming a moment of prayer."
All the major religions bar Sikhism have used fasting to focus the mind in a similar way.
In the Bible Jesus says "Man shall not live on bread alone." His 40 days in the wilderness was the inspiration for Lent, when Christians have traditionally given things up.
Christians use fasting to think about the poor - people who are hungry not through choice but circumstance. It is also seen as aiding concentration and bringing one closer to God. A coincidental benefit for some is weight loss - the Bishop of Manchester loses half a stone (3kg) every Lent.
But there are differences of tone and doctrine over fasting between Catholics and Anglicans.
"A life of unrestrained self-indulgence leads to disaster," says Father Alexander.
He talks about the "mortification" of the flesh - fasting as a form of penance - but Anglicans avoid the word. "It's a spiritual discipline but a joyful one," says Bishop Walker.
But can a secular dieter ever feel spiritual? Bishop Walker thinks so. "If you're open to the fact that this process of fasting will open you up to a spiritual encounter it may very well do so," he says.
Not eating every day goes beyond religion to something basic in nature, Bishop Walker argues. He remembers going to the zoo and seeing a sign on one of the enclosures: "The lions are not fed on Fridays." Carnivores do not need to eat every day, he argues, and nor do we.
Breaking the fast isn't the end of the world, says Father Alexander. His favourite meal is fish and chips, a Friday evening staple at the monastery.
"Some days I say: 'OK guys I give up, I can't take it anymore. I need fish and chips.' I think there's a bit of wisdom in this. It's my own private decision. I don't think fasting is just a matter of self-will, it's about growth and Grace."
So the benefit of fasting may sometimes be outweighed by the companionship of sharing good food, he says. Especially if it's fish and chips for tea.