A lot of diets out there are frankly terrifying. When Google released its rankings of the most-searched-for diets of 2017, most of them sounded like terrible ideas, like the one that says to eat only hard-boiled eggs for two weeks, or the one that involved paying loads of money for mysterious supplements.

But even those seem almost rational when compared with the trendy new "diet" called the "water fast," which is not really a diet at all. It's just not eating food. There's no celery, no kale, and not even a single bean. It's just starving yourself and drinking water and pretending that's healthy.

Brief fasts or "cleanses" where a person consumes only juice or soup have been in the ethos for some time, but water fasting takes that idea even farther. It doesn't even allow a person to have juice, and it doesn't stop after just a week or two. Water fasting involves consuming nothing but water, tea, coffee, and seltzer —which naturally contain zero calories — and it can go on for a month or longer.

Elan Kels, a 36-year-old real estate broker, decided to try it after hearing about it on the internet. He says he'd tried a million diets that had not worked for him. Then he lost some weight by doing intermittent cleanses, but he wanted faster results, so he decided to go even farther and stop eating anything at all for 47 days.

"The idea is: You could do it as long as you have fat on your body, and that's what gives you energy," he told the New York Post.

But human beings are not camels, and experts say going without any calories at all can cause serious health problems.

Eating disorder specialist and clinical social worker Joanne Labiner told the New York Post that water fasting is a kind of disordered eating, and it's potentially very dangerous.

"It can be so bad for your organs. That's why people with anorexia can die of a heart attack. Their body feeds on their heart," she said. "Your body thinks it's an emergency and tries to prevent that fat storage from being used up, and it feeds on the muscle."

"There's lots that's bad about this 'diet,'" agreed dietician Jo Travers, author of The Low-Fad Diet, in an interview with The Independent. "For a start, there are pretty much no vitamins and minerals. Most vitamins are water-soluble and can't be stored, so you need them regularly throughout the day. Then there's no protein, which means the body has to break down muscle in order to recycle amino acids into hormones and enzymes to stay alive."

Elan Kels had meant to go 47 days without eating, but he only made it 28 before he quit because he was too tired to even get out of bed. He lost 55 pounds in those 28 days, but gained the weight back once he started eating again. Because in addition to being potentially very dangerous, water fasting is not even effective.

"When you deny the body the calories it needs, your metabolism slows in an effort to conserve caloric fuel and may be disturbed despite regaining normal eating habits," nutritionist and eating disorder specialist Rhiannon Lambert told The Independent. "Ultimately, these kind of diets will lead to severe nutritional deficiencies and possibly a loss of skeletal muscle."

In spite of the fact that water fasting is ineffective and potentially very dangerous, it is becoming disturbingly popular on social media. There are more than 17,600 posts on Instagram tagged #waterfast, and people are using the hashtag on Twitter and YouTube to talk about their fasts, find people to encourage their calorie restriction, and to encourage other people to starve themselves too.

Travers particularly hates that water fasting is being described as a "cleanse" or "detox" and promoted as though it is healthy, when it very much is not.

"This language is so misleading as 'cleanse' or 'detox' are completely meaningless terms," she told The Independent. "They have a positive feel to them and have a health halo, but actually it's a complete myth. A healthy balanced diet is called a healthy balanced diet because it is healthy and balanced. This is neither."