Warnie credits exercise and a meal replacement drink, recommended by an AFL star, for his twelve kilogram weight loss.

Shane Warne is shrinking rapidly, appearing to be a shadow of his former self. In just four months the spin king has shed twelve kilograms, and claims organic weight loss drink Tai Slim is responsible for the dramatic change.

The former cricketer's new look is fuelling added interest in diet shakes, and that's a worry to health experts who preach a balanced diet.

Diet shakes and meal replacements have become hugely popular across the country, with brands like Tony Ferguson, Optislim, Biggest Loser, Celebrity Slim, Slim Shake and Fat Blaster the highest-selling, in a weight loss industry worth almost $790 million.

What’s with Warnie?

Nutritionist Melanie McGrice does conceded that “sometimes shakes can be a great tool to use,” though she also warns that “a lot of these shakes will have synthetic sugars and synthetic ingredients in them.”

“Most people don’t know what they actually need,” she said.

According to the latest figures from the Australian Bureau of Statistics being overweight is becoming the new norm.

For the first time the number of adults classified as overweight equals the number of people of normal weight - about 37 per cent.

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Dieters seeking to get back into shape are sipping slimming shakes, some with as much sugar as a bag of lollies, according to former body shaping champion Jane Peterson.

“While looking at snack options I was surprised to find there was up to 47 per cent sugar in some of the shakes out there. Fructose is not good for the body as it bypasses the fullness signals, and acts as a fat within the body,” she said.

Peterson saw an opening in the market and has seized on it, creating her very own shake and energy drink.

“Energy Slim only contains 7.5 per cent sugar, so it helps to promote weight loss,” she said.

Meal replacements come in a range of forms such as powders, drinks, soups, bars and biscuits. Some are made to replace all meals, while others replace one or two meals a day, or can be used as a snack, like energy slim.

“Shakes are good for a mid-morning or mid afternoon snack. They are high in protein and satisfy the hunger for longer,” Peterson said.

Nathalie Neys used Energy Slim shakes and liquid formula to drop the weight she gained during pregnancy.

The short-term benefits of slim shakes can include rapid weight loss, keeping temptation away, and having a quick and convenient way to prepare meals on the go.

However, if you lose weight too quickly, you risk developing gall stones.

You can also lack fibre and increase your chances of getting a hernia. It's generally an expensive diet method, and your weight can fluctuate.

The side effects range from headaches and dizziness to constipation, diarrhea and mood swings. But, despite the persuasive promises on the packages, there are very few studies establishing what works best.

Nutritionist Melanie McRice advises to beware of diet products like the Energy Slim Liquid Formula, which claims to assist your metabolism, but has no nutritional value.

“You pretty much get the same effect from (the shake) as you would from having a cup of coffee each day, so I’d just say it’s an expensive cup of coffee.”

According to the Dieticians Association of Australia, 95 per cent of all dieters will regain their lost weight in one to five years.

Zein Faraj decided to overhaul his diet and exercise, with no fads and no gimmicks. The result was losing 90 kilograms in nine months.

“I make healthy choices. Instead of frying something, or baking, I’ll grill it instead. I also do about two to three hours of exercise,” Faraj said.

“I was 186 kilos and now I'm 95. I never have been a believer in fad dieting. It’s more than a diet change, it’s a complete lifestyle change.”

If you still want to try a shake, you should see guidance from a doctor of health profession. You should avoid meal replacements if you are pregnant or breastfeeding, under the age of eighteen, or if you are suffering from Type 1 Diabetics, kidney or liver disease.

The best option is to change your diet to a healthier option, and increase your exercise.