NEW YORK (CBSNewYork) – From the “thigh gap” to the “bikini bridge” there have been some pretty unrealistic body image pressures on teens in recent years.

The latest is called the “Cinderella Challenge.” As you may have guessed, it has girls starving themselves to look more like the fictional princess.

Once upon a time, a viral weight loss trended, called the “Cinderella Challenge,” swept through social media.

“The end game or the goal is to develop a body with Cinderella-like proportions, with that unrealistically tiny waist,” Dr. Barbara Greenberg explained. “Only for a fictional Disney character.”

Yet, take a look on Twitter and you’ll find posting after posting from young women fooled by the fairy tale, she says.

“This really may seem innocuous at first, but it’s actually quite dangerous,” said Greenberg. “To get that body, they engage in strenuous dieting, get frustrated and start to dislike their bodies. And sometimes the dieting can lead to eating disorders.”

The goal weight of the challenge is calculated by taking a person’s height, converting it to meters, then squaring that number and multiplying the total by 18. So for example, the Cinderella weight for a woman that’s 5 feet 11 inches tall would be 128 pounds.

“I wouldn’t suggest anyone do it,” said one teen who’s tried the trend. “You want to have a BMI of 18. So that’s definitely an underweight BMI. And you want to eat as little amount of calories as possible during the day.”

She restricted her diet to as little as 500 calories as day.

“Not eating very much is really hard,” she said.

“There’s a lot of pressure not only to do well in school, to have friends, to achieve,” Greenberg said. “And one of those achievements is an unrealistic pre-pubescent looking body, which is impossible for a young girl who has reached puberty.”

Greenberg said the challenges often turn into an online competition.

“If you can achieve the thigh gap or if you can achieve a Cinderella sort of body, you become a member of what the girls think of an exclusive superior club, and that’s the problem,” she said.

With potentially dangerous consequences, she says it is important for parents to monitor teens’ online activity.

“Nine out of 10 teenage girls don’t like their bodies. That’s a very high percentage,” she said. “Be aware of what the trends are and talk to their girls about that.”

While the “Cinderella Challenge” is gaining popularity with girls in their late teens and early 20s, Greenberg said girls as young as eight years old are developing eating disorders, and the impact of social media is largely to blame.