The MC is not a weight loss diet and does not work by the restriction of caloric intake. It is a "fast" where the system actually enters into Ketosis which is a state characterised by elevated levels of ketone bodies in the blood, occurring when the liver converts fat into fatty acids and ketone bodies (which can be used by all of the body for energy as an alternative to glucose).
This is part of a survival mode where your system will use up fat reserves way before it starts using healthy tissue (muscle) and since you are also ingesting a good amount of carbs/glucose with the syrup there is little need to start using any vital tissues for energy. The human system is a very smart machine and when it goes into survival mode it will use up not only fat but it also uses up damaged and dead cells for energy before it goes into any vital tissues such as muscle. That is the basic principle of how "fasting" works as a healing modality.