[2] A PSMF attempts to spare the dieter the health risks of a complete fast by introducing the minimum amount of protein necessary to prevent muscle-wasting effects, while still eliminating fats and carbohydrates.
[6][7] The concept of "protein-sparing modified fast" (PSMF) was described by George Blackburn in the early 1970s as an intensive weight-loss diet designed to mitigate the harms associated with protein-calorie malnutrition[8] and nitrogen losses induced by either acute illness or hypocaloric diets in patients with obesity, in order to adapt the patient's metabolism sufficiently to use endogenous fat stores as well as to preserve the protein contained in the body cell mass.
Three years later, in 1979, Isner published a report of 17 deaths associated with liquid protein VLCD, due to heart-related causes.
As a result, a review was published that highlighted the differences between these liquid protein diets, arguing that the fatal diets typically used hydrolyzed collagen (gelatin) supplemented with the amino acid tryptophan for protein but that this omitted the other 8 essential amino acids; it further emphasized the importance of close medical monitoring during the fast and refeeding periods.
[13] Instead of hydrolyzed collagen, modern medically supervised PSMF diets include foods of higher biological value, such as meat, fish, eggs, cheese, and/or tofu.