Shane Warne: Do liquid diets work and are they safe?

Diets based on juiced fruit and vegetables are high in vitamins but often low in calories, protein and fibre

Shane Warne, who died from natural causes on Friday, had reportedly been on a liquid diet for 14 days - to try to lose weight quickly.

Days before he died, he tweeted an old photo, saying: "The goal by July is to get back to this shape from a few years ago."

Friends have said it was a regime he had tried several times before, although there is no evidence it was linked to his sudden death.

So how safe are these diets and what is their effect on the body?

There are many different kinds of liquid diets but they all have the same aim - to lose weight quickly by eating fewer calories.

They range from fashionable fruit and vegetable juice drinks that promise to detox and cleanse the body to low-calorie shakes and soups.

But experts warn these extreme diets carry health risks and are unsuitable for most people.

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The NHS recommends its 800-calories-a-day diet for certain groups only, particularly obese or severely obese people managing type-2 diabetes.

Tried and tested, it comes with lots of support and medical supervision, and contains all the daily nutrients needed - but this is seldom the case with other liquid diets found online.

"Juice diets appeal to people because they want a quick fix - but dieting is really hard," Aisling Pigott, of the British Dietetic Association, says.

"There is a role for them - but it's not one size fits all.

"It's concerning when they are marketed at people who are a healthy weight."

Fruit and vegetable juice provides lots of minerals and vitamins - but very little protein or fat.

Even fibre would be in short supply unless the whole fruit, including the skin and seeds, was pulped and added.

"You'd feel drained and exhausted after a week," Dr Gail Rees, associate professor of human nutrition, at the University of Plymouth, says.

A diet that is not nutritionally balanced is not giving the body everything it needs - and "could be very damaging" in the long term.

Iron reserves would be used up, which could lead to anaemia in women, muscle mass would be depleted and the gut, lungs and liver would have to work harder to keep the body functioning normally.

Other potential side-effects include headaches, dizziness, extreme tiredness, diarrhoea or constipation.

Fruit juices, which contain lots of naturals acids, can also wear away enamel on teeth and a lack of calorie intake can make breath smell different.

Losing weight quickly is possible on a liquid diet but the biggest challenge, according to Ms Pigott, is "yo-yo risk" - the danger of piling weight back on again when food intake returns to normal.

Fad diets are "part of a toxic diet culture" encouraging negative attitudes to food and often leading to weight gain not loss, she says.

And she recommends listening to your own body, going back to basics and setting achievable goals that work in the long term, not just for a week.

'Weight cycling'

"Extreme diets are not a sustainable solution for losing weight in the long term, as much of the weight that is lost is likely to be water or lean muscle," Dr Simon Steenson, of the British Nutrition Foundation, says.

"These types of crash diets may also lead to some health risks as well, such as a higher risk of developing gall stones."

Dr Steenson also warns of "weight cycling" - a pattern of losing and regaining weight with fad diets - which can have negative health effects itself.

A better option to lose weight, he says, is to aim for a varied and balanced diet, including lots of fruit, vegetables, wholegrains, beans, nuts and seeds, plus finding ways to be active throughout the day.

Dr Rees recommends removing alcohol, crisps, biscuits and takeaway food from your diet, which are all supplying unwanted calories, rather than focusing on a quick "liquid diet" fix.

And if you have any underlying health conditions, always check with a GP or dietitian before starting a diet.

Carried out in the right way, liquid diets - such as the low-calorie NHS programmes for the overweight - are proven to work, but for many people, they can be very difficult to follow and may be unnecessarily risky.