“Any extreme low-calorie diet is associated with side effects, kidney stones, dehydration, headaches,” Dr. Aronne said, “and if you lose muscle mass and water, what’s the point of that?”

While the tube diet is fairly unknown in this country, it has been popular for years in Italy and Spain, where it is used casually to lose weight before a big event, as well as for more significant weight loss. In England, where it has been offered for the past year as the KEN (or ketogenic enteral nutrition) diet, The Daily Mail asked if it was “the most extreme diet ever,” before adding that a National Health Service doctor was offering it.

Dr. Scott Shikora, the director of the Center for Metabolic Health and Bariatric Surgery at Brigham and Women’s Hospital in Boston, said: “Putting a tube in one’s nose, it’s not always comfortable and pleasant. And this has to be medically supervised.”

Ms. Schnaider had the tube removed early, not because of discomfort, but because she was losing too much weight, reaching 127 pounds, 10 pounds down, in eight days. Her wedding is scheduled for June in her native Argentina.

“At first I decided not to do it for people who just want to lose a few pounds,” Dr. Di Pietro said. “But then I thought, why should I say 5 or 10 pounds are not enough? People want to be perfect.”

They are willing to pay for it: $1,500 for the 10 days, which includes a screening and the equipment. They also have to feel confident enough to wear the tube in public.

“People think I’m sick, I’m dying,” said Ms. Schnaider, a watch wholesaler in Miami. She refrained from going into her daughters’ school. “The children, they would be scared,” she said.

Dr. Shikora said any caloric restriction will lead to weight loss. “The novelty is, they shove a tube in your nose,” he said.

“It doesn’t matter if it’s through a tube, a straw, a meal plan,” he said. “They all work, if someone goes from 3,000 calories a day to 800.”

The problem, critics of these programs say, is crash dieting in general.

“I don’t want to tell a bride she shouldn’t look good for the wedding,” Dr. Aronne said. “But we tell them, ‘You can get to the same place if you started earlier, instead of waiting until the last minute and doing something drastic.’ ”

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By LINDA LEE