PetMD states that cats eat grass for reasons related to nutrition and digestion. The juices in grass contain folic acid, an essential vitamin that helps the bodies of cats function optimally and helps produce hemoglobin in their blood. Grass can also be a natural laxative for cats.
According to PetMD, another theory suggests that the regurgitation that results when cats eat grass helps clear the digestive tracts of contents that they are unable to digest. Cats eat their prey whole but cannot digest bones, feathers and fur, so cats have to find ways to get these contents out of their digestive tracts.