Protein Sparing Modified Fast, what is it?

"The Protein-Sparing Modified Fast (PSMF) is designed for rapid weight loss and incorporates medical, nutritional, and behavioral components. The goal of this diet is to reach an appropriate body weight as determined by your physician and dietitian.
Carbohydrate, protein, and fat are the nutrients in food that provide energy for proper functioning, maintenance, and repair of the body. In addition to these three nutrients, the human body requires water, vitamins, and minerals for good health.
While on the PSMF program, only lean meat, seafood, poultry, and a limited amount of low-carbohydrate vegetables should be eaten. Carbohydrates and additional forms of fat are not allowed on this program. The high protein intake is to prevent the body from using its own protein stores in muscles, tissues, and cells for energy. Thus the program is a "modified" fast.
Carbohydrates are usually the body's primary source of energy. Since a very limited amount of carbohydrates are consumed, fat becomes the primary fuel source for the body. This rapid breakdown of fat produces ketones that spill into the urine, called ketosis. Ketones in the urine are desirable. While in ketosis, most people lose their appetite, which is a benefit of this program. A large amount of the water in your body is stored with carbohydrates. Since carbohydrate intake is severely limited and storage is severely depleted, dehydration is a health concern. To compensate, adequate quantities of fluid, sodium, and prescription potassium are required each day. Eating foods that are not appropriate can stop ketosis, which not only means less weight reduction, but it can cause dangerous shifts in the body's fluid and electrolytes."

PSMF Diet Program