The paper cup diet is a Korean diet invented by Korean starlets, the K-Pops. These are often extreme diets that take their first name or stage name, and which from Korea have since become famous among girls who try diets on the web.
Obviously these are drastic diets because they are very low-calorie, therefore risky for those who follow them.

They are not created by doctors, but invented by girls and imitated by their fans. This already makes them extremely questionable.
One of the most famous diets among the K-Pop diets is precisely the paper cup diet.

THE PAPER CUP DIET OR K-POP DIET

The paper cup diet is based on a plastic cup as a food meter. A drastic version (the plastic cup is smaller than the glass one) of Doctor Mascaro’s glass diet.
Basically, you only have three meals a day with the help of glasses, for a total of 900 calories per day.

For example, for breakfast you eat a glass of mandarin wedges, a piece of banana and a glass of milk.
For lunch we eat a glass of cooked brown rice, two glasses of vegetables, a glass of low-fat yogurt or chicken breast. For dinner, always a glass of cooked brown rice, two glasses of vegetables, a glass of cottage cheese or shrimp tails. When the contents of the glasses are overturned on the plate, one immediately notices that there is very little food.
Only zero-calorie drinks are not counted.

The risk of such a diet is to lose lean mass, to slow down the metabolism with future problems in losing weight and to run into serious food shortages, since this diet should in theory be followed for at least a month.

A madness that I hope only minors can think of, and that must be absolutely forbidden to them, teaching girls a healthier lifestyle and the importance of movement if they want to lose a few pounds, but also the importance of respecting their body and above all their health.
For those who have heard of the glass diet, perhaps they were looking for the official diet, that of Dr. Mascaro, designed for adults but always in agreement with their doctor. A non-restrictive diet however developed by a doctor that you can read here.