It's the hot new spot for Euro A-listers looking to lose weight, but the treatment offered by Austria's Viva Mayr clinic has been slammed by top Kiwi nutritionist Nikki Hart.

Celebs such as Sarah Ferguson are flocking to the $6000 a week retreat, where they're told to chew each mouthful of food up to 40 times and drink two or three litres of water a day.

Hart said they were wasting their money - and could lose weight just as well without spending a cent.

"It's just another bizarre fad that I am sure will be replaced by something equally bizarre within the next month.

"This resort is basically just reducing calories by filling a person up on low-calorie fluids and slowing energy intake by imposing eating rules like chewing times."

The clinic, on the shores of Austria's Lake Worth, is not so much a fat camp as a luxury retreat.

Reportedly popular with celebrities, businessmen and Russian oligarchs, Viva Mayr is known for a strict regime said to purge the body of toxins, end digestive problems, boost energy and leave you feeling slimmer and lighter.

Hart said dieters would be better off using common sense - eating healthily, avoiding giant portions and exercising regularly.

"Sensible nutrition is boring, but it works, it just isn't as marketable as a fad diet."

While the Euro elite head for the Austrian Alps, Kiwi celebs are more likely to book in at the Golden Door and Gwinganna in Australia.

The Golden Door has a resort in Queensland and a newer branch in the Hunter Valley.

Both offer intensive seven-day programmes that, for between $2500 and $3500, promise to leave you feeling wonderful.

Stimulants like caffeine, sugar and alcohol are replaced by gourmet vegetarian cuisine, pampering and luxury surroundings.

Gwinganna opened in 2006 on the Gold Coast and also offers a seven-day detox programme.

At up to $5000 for a week, it makes the Golden Door look almost affordable - but that's not stopping increasing numbers of Kiwis checking in.

Spokeswoman Tracy Willis said most were women aged 40-plus who live hectic lives.

They've also had a few "high-profile Kiwi business people", but Willis isn't naming names.

Gwinganna offers a very gentle detox.

Caffeine, sugar and alcohol are banned, but guests eat a delicious seafood-based diet and don't have to exhaust themselves.

Exercise can be as gentle as a few yoga classes and there is plenty of downtime for a massage or facial.

No wonder it's popular with the Australian arm of the Hollywood elite - Hugh Jackman's a regular, and Naomi Watts, Nicole Kidman and her New Zealand-born husband Keith Urban have all visited.

Hart said weight-loss resorts can be good for "getting people back to basic nutrition", but the problem is what happens when the week is over.

Four fad diets
ATKINS

Severely restricts carbohydrates, allows a lot of protein and fat.

Hart's verdict:

More protein decreases appetite, so you stay full for longer. But it removes calcium and is linked to high fat levels. "This is not a bad way to go, but not long term."

THE ZONE

High protein and limited carbs, but not as extreme as Atkins. Renee Zellweger said to be fan.

Hart's verdict:

"When you limit carbs, you're losing a lot of water, but it looks like fat loss on the scales. When you go back to a normal diet the weight comes back on."

DETOX DIETS

Claim they can "cleanse" the system. Beyonce reported to be fan of diet where you drink only a mix of maple syrup, lemon juice, water and cayenne pepper.

Hart's verdict:

"If you were to eat more fruit and vegetables, limit alcohol, eat more fresh grains and that kind of thing, that's a detox in itself."

GRAPEFRUIT DIET

Eat half a grapefruit before every meal. Enzymes are supposed to make you magically lose weight.

Hart's verdict:

Just another fad. Grapefruit interferes with oral contraception.