LOSING weight seems to be a lifelong mission for many girls. As an alternative to the traditional way of eating less and exercising regularly, a group of fad weight-loss recipes have gained popularity recently, claiming to have instant effect without cutting out meals.

But nutritionists warn that some of the recipes may damage the body in the long run.

Cindy Zhen, 25, who disappeared from dinner gatherings for two weeks, happily returned with a new look that astonished many of her friends. She lost 4 kilograms within the two weeks, reaching her ideal weight of 52 kilograms.

Instead of using the traditional weight-loss methods such as eliminating all high-calorie foods and physical exercises, Zhen achieved her goal simply by following a diet recipe that does not even skip steak for dinner.

“I want to lose weight” is every young woman’s mantra, especially as summer is here. They want long, slim legs, a wasp waist, defined collarbones, a nice bottom and narrow chin, like models on runways, TV and in advertising.

Many try various methods such as starving themselves, taking laxatives, or drinking black coffee so as to achieve their goal. Many give up in frustration when they fail to reach their expectation.

Zhen followed the so-called “Copenhagen Diet,” a weight-loss method that nobody knows exactly where it originated and only got popular in China a couple of months ago.

It’s a 13-day program that claims to help people burn fat by improving metabolism. Those who strictly follow the recipe of three meals a day for 13 days can lose 7 to 20 kilograms without any physical exercise involved, its practitioners claim. And the improved metabolism will keep working even after finishing the 13 days.

It is advised not to repeat the recipe for two years. The Copenhagen Diet gives very detailed instructions on the ingredients and quantity for everyday meals.

Most diets emphasize a rich and healthy breakfast with a relatively plain dinner. Under the Copenhagen Diet, people eat a very limited breakfast, plain lunch and relatively rich dinner.

For breakfast, it calls simply for a cup of black coffee and a cube of sugar, while a slice of baked bread and a carrot are added on some days.

For lunch, you get two eggs and some vegetables, while on some days 200 grams of ham, codfish or yogurt can be substitute.

However, 200 grams of steak together with vegetables appear on the dinner menu most days; 200 grams of mutton or 250 grams of chicken are sometimes substituted for the steak. No staple foods are included for lunch and dinner.

“It is a very attractive recipe for me not only because it promises an instant effect on losing weight, but also for it not being a boring recipe that involves eating nothing but vegetables,” says Zhen. “I like meat. That’s why I gained weight in the first place. The recipe impressed me so much as it indicates a way of losing weight by eating meat.”

It is not the only recipe winning young women’s favor who desire a quick weight loss. The Dukan Diet got worldwide fame when Kate Middleton, now Duchess of Cambridge, gained her slim figure before her wedding by following it.

Instead of giving detailed recipes, the Dukan Diet gives guidelines for four different recipes in four phases. They are eating pure protein in the first phase, eating pure protein and pure vegetables by turns in the second phase, adding one fruit and two slices of wheat bread to protein and vegetables during the third phase, and getting back to a normal diet in the fourth phase.

The number of days in each phase depends on how much weight practitioners want to lose. It is said to be effective in helping get rid of at least 6 kilograms in a month when properly followed.

“Juice fast” that promises to take effect in three days is also attractive. By following this recipe, practitioners consume nothing but six kinds of fruit or vegetable juice every day. They need follow the diet for only three days. The recipe is said to provide rich fibers, vitamins and mineral substance that helps the body expel toxins while providing enough energy for daily activities.

In spite of the instant effect, nutritionists suggest people think twice before following this diet, as it might pose long-term health risks.

Both the Copenhagen and Dukan diets are based on the same concept of breaking the normal digestion and absorption procedure by eliminating carbohydrates. That idea has been discussed and debated for years in the nutrition science field, says Dr Yang Kefeng at the Nutrition Department of the Medical School of Shanghai Jiao Tong University.

Proper portions of carbohydrates, fat and protein are essential for guaranteeing proper digestion and absorption within the body. Without carbohydrates, the foods that the practitioners take (mostly protein in this case) won’t turn into the energy that supports daily activity, so the stored energy (fat) will be used instead.

“It may take instant effect in burning fat because what the practitioner eats will not be absorbed, but pose a very dangerous health risk by producing extra toxin within the body,” says Yang.

Without consumption of sufficient carbohydrates, the body will accumulate extra ketone in the blood, which will eventually harm the kidney, says Yang.

“Some practitioners may quickly find their urine ketone bodies exceed the standard,” says Yang. “Though there may not be instant symptoms for young healthy people, it will be very dangerous for those suffering kidney-related problems already,” including people with diabetes, urethritis and kidney stones or inflammation.

This is likely the major reason why the diets suggest not doing it for too long.

Of course, many of the extra urine ketone in young people will decrease when they cease the diet, but it is still uncertain whether the hidden risk will stay in the long run, says Dr Yang.

Juice fast seems to be a relatively healthy short-term diet, but Yang warns that doing it long term may lead to malnutrition.

The traditional method of losing weight — focusing on a balanced diet, smaller portions, less fat, carbs and sweets, and regular physical exercise — is still the most recommended. But it requires patience because it takes longer than the quick, fad diets.

All food groups provide important nutrition, so it is better to reduce the portion instead of eliminating any group. Getting individual suggestion from a professional nutritionist is always very helpful.

Regular aerobic exercise (at least 30 minutes a day) like jogging and brisk walking can help burn fat effectively.