From the Manufacturer:
The leaves of the Nopal cactus have the unique ability to bind and trap fat and certain sugars consumed during a meal and prevent their absorption into the body. Reducing the amount of fat and sugar absorbed during a meal may play a key role in cholesterol metabolism as well as weight reduction.
Chitosan, a common dietary supplement, exhibits similar actions, but is derived from shellfish. Nopal cactus offers vegetarians and those allergic to shellfish an effective alternative to chitosan.