Fasting has exploded in popularity, and the benefits have been found to extend far beyond weight loss. Studies suggest it can reverse type 2 diabetes, slow the onset of Alzheimer’s and help reduce the risk of heart disease and certain cancers.

Advocates also enthuse that fasting disrupts negative eating habits, such as snacking, and resets our relationship with food.

‘Studies are increasingly showing that our bodies are used to shutting down for periods of time and not having food,’ says Tara Kelly, a research associate dietitian who studies the effects of fasting at Newcastle University.

‘We don’t know all the answers yet, but we do know that our modern habit of consuming and snacking all day long isn’t how our bodies are designed to eat. It’s not so much what we eat but when we eat that has the most impact on our health.’

[Ketogenic, intermittent fasting, zone: which diet is best?]

A study by a team of researchers at the University of Graz in Austria, found that restricting your calories every other day – also known as ‘calorie cycling’ – lowers cholesterol levels, improves heart health and extends life expectancy in otherwise healthy adults.

Experts agree that fasting is not suitable for everyone and should be avoided by certain groups, such as children and teenagers, pregnant or breastfeeding women, the over 70s, and those with any history of eating disorders – and very importantly, you should seek medical advice before beginning any kind of extreme diet regimen.

So, which one is right for you?

Fasting for... weight loss

Professor Valter Longo, a gerontologist at the University of Southern California and a leading fasting expert, has developed the ProLon diet (it stands for pro-longevity), which is a five-day diet, with calories limited to 500 per day, that mimics the effects of fasting.

Fans include Benedict Cumberbatch.

Those who have tried it say their sugar cravings disappeared and quality of sleep improved. 

You can do it a maximum of two to three times a year as a reset for your metabolism.

If you’re overweight, however, Longo advises doing three fasts one after the other, with a month’s break in between.

Research by Prof Longo on 100 people found those who did his five-day diet every month for three months lost weight and body fat and also saw improvements in blood pressure, cholesterol and the hormone insulin-like growth factor-1 (IGF-1), which is linked to ageing and disease.

For gentler, more gradual weight loss, time-restricted eating may be more suitable.

Fasting for... brain health

Studies have suggested that fasting can delay the onset of Alzheimer’s and other neurological conditions, like Parkinson’s.

‘Fasting is a challenge to your brain, and we think that your brain reacts by activating adaptive stress responses that help it cope with disease,’ says Mark Mattson, a professor of neuroscience at the Johns Hopkins School of Medicine.

‘From an evolutionary perspective, it makes sense your brain should be functioning well when you haven’t been able to obtain food for a while.’

Some believe that cutting down calories dramatically for periods of time boosts our cognitive performance.

Dietitian Helen Bond says that intermittent fasting, or time-restricted eating, has some good observational studies linking it to a reduced risk of Alzheimer’s and improved cognitive ability.

Fasting for... diabetics

The evidence for fasting is strongest with type 2 diabetics.

Researchers at Newcastle University put 11 people with type 2 diabetes on a 600-calorie a day diet for eight weeks, after which time all were disease-free. Three months on, seven were disease-free.

The team believe weight loss from fasting reduces fat inside the liver and pancreas, allowing the organs to return to normal function.

Dr Mosley, who credits fasting for reversing his type 2 diabetes, recommends kick-starting your weight loss with an 800-calorie-a-day fast, for between two and 12 weeks and then, once you’re nearing your target, switching to a 5:2 diet.

A study from the University of Alabama found that pre-diabetic patients who did early time-restrictive eating helped ward off diabetes.

Diabetics should always consult their GP before beginning a fast.

The Daily Telegraph