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Last year, the usually pumped-up rapper 50 Cent posted photographs of himself on Twitter looking frighteningly emaciated. His gaunt appearance was nothing to do with an eating disorder or any other illness -- he lost the weight for a part as a cancer sufferer in the movie Things Fall Apart -- but the speed at which he shed the pounds got people talking.

In the space of nine weeks he lost almost four stone, dropping from 15 stone to 11 stone and shedding six inches off his waist. His secret? A liquid diet.

Despite the rise and fall of fad diets that restrict certain food groups and promote others, from Atkins to GI to the now-popular Dukan diet, the liquid diet has always been in fashion, particularly with celebrities.

While Buffy was slaying vampires, Sarah Michelle Gellar swore by the infamous cabbage soup diet. When Sarah Jessica Parker was strutting her stuff in Sex and The City, she routinely resorted to an all-liquid diet comprised of daily drinks, including pineapple-apple-mint juice and cashew-nut milk. Beyonce has long been an advocate of the maple syrup diet, which comprises of a concoction of lemon juice, water, maple syrup and cayenne pepper, and now counts Cheryl Cole as one of its followers. And to keep her body A-list for three rom-coms a year, Jennifer Aniston makes no bones about her pureed baby food diet.

Celebrities may be fans of liquid diets, but not all nutritionists are. Seemingly chewing food, rather than drinking it, helps release nutrients. The longer food remains in the mouth, the experts say, the more signals are sent from our brains to our stomachs to release the necessary digestive juices. The more digesting you do, the fuller you feel for longer. So if you consume your food as a liquid, it's more likely you're going to feel hungry more quickly.

Liquid dieting is also ultimately self-defeating, according to Daniel McCartney of the Irish Nutrition and Dietetic Institute.

"One of the things we see is that people go on a liquid diet for a particular amount of time during which they lose weight, but afterwards they revert to their previous, solid food diets and the weight comes back on."

And not only will the weight come back on, McCartney says, you will end up heavier than you were before.

"People who lose weight and then regain it tend to end up heavier than they were before they started dieting. When people lose weight, particularly if they lose weight quickly, they lose a disproportionately large amount of their active muscle tissue. The follow-on from that is their metabolic rate drops, in other words the amount of energy they use becomes less. So they are always predisposed to gain more weight if they revert to their original eating habits."

McCartney may be against liquid dieting, but US researchers have found that including liquidated food in your diet can result in weight loss. Researchers at Penn State University secretly added pureed cauliflower, butternut squash and carrots to the favourite meals of 20 men and 21 women. While the subjects did not register any difference in flavour, they ate between 200 and 350 fewer calories per meal.

The same researchers found in 2007 that people who ate a bowl of soup before their main meal reduced their calorie intake by up to 20pc. After feeding a basic chicken soup to both men and women before dinner every day, they found that no matter the consistency, soup helps dieters eat less because it was filling but contained fewer calories.

While the rapid weight loss exhibited by 50 Cent for his movie role was widely criticised as being dangerously unhealthy, in June nutrition researchers Newcastle University in the UK came out in favour of extreme liquid diets. After feeding participants a super-low calorie liquid diet for eight weeks they found that not only was there an average weight loss of two stone, but that it resulted in a reversal of Type 2 diabetes in people newly diagnosed with the condition most associated with obesity.


However, despite this benefit, McCartney, who also lectures in Human Dietetics at DIT, says rapid weight loss is dangerous.

"If you lose weight rapidly over a short amount of time it can damage internal organs like the heart and the liver. They can cause what are called electrolyte shifts, which can cause the heart to beat out of sync."

So, the way forward for the liquid diet seems to be using it as part of your every day menu rather than using it to replace your menu for periods of time.

The rise of the five-a-day smoothie drink on supermarket shelves is a good indication of the way nutritionists are thinking in this department.

Provided a smoothie contains at least 150ml of fruit juice and 80g of pulped fruit or vegetables (with no added sugar or dairy), it will count as two servings of your five-a-day recommended fruit and vegetable consumption.

Even if adding liquid foods to your diet, such as smoothies, doesn't give you Jennifer Aniston's body, you can always take comfort in the fact that you are giving your body the nutrients it needs.

"Although eating fresh fruit and vegetables during the day gives you the same effect," says McCartney, "for people who don't like vegetables these smoothies can often be a pragmatic alternative."

Daniel McCartney is a member of the Irish Nutrition and Dietetic Institute, www.indie.ie