The cabbage soup diet works in the short term due to a couple of processes. First, the caloric intake is reduced to near starvation levels on the cabbage soup diet. Any diet will work with that level of caloric intake. Second, a lot of water and muscle tissue is lost due to the types of food consumed.
The cabbage diet soup diet does work because it tends to make your bowels work very well. It does mostly only work while you are on it because you are losing alot of fluid, but when you go off you normally will gain the weight back.