The 16:8: Is this 2019's most successful diet?

When you are on any kind of intermittent fasting, you can – in theory – eat what you like at the meals you do take. But that's rather missing the point – and will slow down weight loss. Photo / Getty Images

Marketing consultant Kate Beavis is only really hungry twice a day: at 11.30pm and at 11.30am. "My problem has always been late-night snacking," says Beavis, "that's when I feel obsessively hungry. It takes over my brain. Then that hour or so before lunch, that's hard, too. Apart from those moments, I'm fine."

Beavis, who lives in Cranfield, Bedfordshire, with her husband Adam, and their two children, aged 11 and eight, is a new devotee – like much of the UK, it seems – of time-restricted eating (TRE), a form of intermittent fasting.

This is the latest kind of eating plan where you don't restrict what you eat, but when you eat: keeping meals within a tight eight- or nine-hour window.

For Beavis, that means dinner by 9pm and then, skipping breakfast, eating nothing until 1pm the next day, meaning she goes without food for 16-hour stretches. As a result of following the so-called 16:8 diet, in the past four weeks, she has lost 5.4kg.

Marvellously uncomplicated, it's a regime that has spread across Hollywood, with actors like Halle Berry and Vanessa Hudgens being fellow breakfast-skippers. It's flexible, too: you can reverse the window to miss dinner, ending your food day at lunch as Nicole Kidman and Hugh Jackman do.

Fasting is an eating regime with its roots in Eastern philosophy – traditionally, many Buddhists follow the one-meal-a-day philosophy. But the rising popularity of skipping meals owes more to the 5:2 diet, which suggests we eat normally for five days and mostly fast on the other two.

Dr Michael Mosley, the BBC broadcaster, launched the idea of 5:2 on the world in 2012, suggesting this way of eating could be the key to living longer by losing weight and preventing or halting diseases such as type-2 diabetes.

He calls TRE "the new kid on the block", saying: "There are different types of intermittent fasting, and I suspect that they suit different people.

The benefits of intermittent fasting

"With both 5:2 and TRE, you induce a state of mild ketosis" – the name for when the body starts burning fat for energy, having run out of carbs – "and that seems to produce some widespread benefits. One of the most obvious is weight loss, but there is also some evidence that doing intermittent fasting will improve your insulin sensitivity and also reduce blood pressure. Putting rats on an intermittent fasting diet promotes the growth of new brain cells, but this is yet to be shown in humans."

When Mosley first came up with the 5:2, he followed the regime devotedly, keen to avoid the fate of his father, who died of heart failure at 74, having been overweight and suffering type 2 diabetes. Now, Mosley says: "I have added time-restricted eating to my daily habits. I do try to do one day of calorie restriction a week, and include TRE 14:10 [limiting mealtimes to a ten-hour window] most days."

The research

So popular is intermittent fasting – and with so much potential to help the global battle against obesity – it's now the subject of numerous studies.

For example, last month, US researchers from Baylor College of Medicine, Texas found that the dawn-to-sunset fasting practised by Muslims during Ramadan had promising implications for obesity. They reported in the journal Digestive Disease Week that daily fasting increased the level of proteins that improve the way our bodies use insulin and protect us against the risks of a high-fat, high-sugar diet.

And in April, researchers from the University of Adelaide, Australia, published a report in Obesity that showed time-restricted eating – to a nine-hour window – helped men control blood glucose levels.

For Janette Smith, an HR manager from west London, TRE means just one meal a day – which can be any size or shape. "I've tried endless diets, and they always fail because they're such a faff and so pernickety. These days, all I do is eat once a day, and it doesn't matter what time of day I do it."

Usually, says Smith, that means supper, "because that's the meal I want to share with my husband and kids, but if I've got a work lunch, I'll skip food in the evening.

"The key is that at that meal, I do eat whatever I want, including pudding and cheese, and I also drink wine if I feel like it."

So popular is intermittent fasting - and with so much potential to help the global battle against obesity - it's now the subject of numerous studies. Photo / Getty Images

She adds: "I'm an all-or-nothing kind of person, and can't stand nursing a mimsy little plate of steamed plaice and boiled broccoli. I'd rather not eat at all and save my calories for a dollop of burrata and a glass of wine in a few hours."

Despite the "no-rules" concept, Smith is strict about one thing: "I never cheat and I never snack. Today's tricky because I had lunch yesterday and I'll have supper tonight, which means so far I've fasted for 25 hours and I'm not eating for another four, so my tum is rumbling.

"It wouldn't suit everyone, but I'm not the kind of person who faints if they don't graze. And it works: I've lost 22lbs (9.9kg) in three months and can see myself carrying on like this forever."

Beyond dieting

For Kate Beavis, the 16:8 isn't about dieting. "I've been heading towards menopause and all the symptoms coming with that," she says, "such as headaches, teenage-style acne and sore breasts. But I had also put on a stone in weight, too, which I wasn't happy about, taking me up from a size 10 to a 12."

Beavis heard about the idea of intermittent fasting by accident as a way to regulate hormones and kickstart the metabolism. She says: "My interest in TRE is as a lifestyle, not a diet."

Rick Hay, a nutritionist and author of The Anti-Ageing Food & Fitness Plan, also follows a TRE routine, leaving a 12-to-14-hour gap between dinner and breakfast. He says: "I follow this off and on when I need to drop a few pounds. It helped me to lose over 10lbs (4.5kg) late last year, and I have kept the weight off."

What the experts stress is that when you are on any kind of intermittent fasting, you can – in theory – eat what you like at the meals you do take. But that's rather missing the point – and will slow down weight loss. Mosley recommends that when you do eat following a Mediterranean diet, rich in fish, vegetables, fruit, nuts and olive oil.

Could intermittent fasting work for you?

If you fancy joining the TRE movement, Hay has a few tips. "To start with, don't do it every day," he says. "Build up to it, and if you are doing a one- or two-week stint, you can always have a day off."

Mosley, who now offers an intermittent-fasting programme online called The Fast 800, adds: "The main thing is to plan ahead and to know why you are doing this. What is your goal?

"It is a good idea to join an online community, for advice and support, and certainly to get your friends and family on board before you start."

But fasting isn't suitable for everyone. "There are quite a few people who really shouldn't approach any form of dieting without being very cautious," says Mosley. "This diet is not suitable for under-18s, or if you're breastfeeding, pregnant or undergoing fertility treatment. Do not do it if you are underweight or have an eating disorder, and discuss it with your GP if you are on medication or if you have a medical condition."

Having seen the results, Kate Beavis is certain she will stick to a form of TRE for the foreseeable. "I feel I am re-training my brain," she says. "The weight loss has been a bonus, but the benefits have been life-changing."