There can be multiple causes, including medications and sometimes it's specific to certain enzymes being low, so it's hard to generalize. An an example, a low B.U.N., or Blood Urea Nitrogen can be due to poor diet, malabsorption, or liver damage. A lowered creatinine
level may result from kidney damage, protein deficiency, pregnancy or liver disease. From what I understand the 'general' reasons for decreased liver enzymes include the following: malabsorption, poor diet, diet low in foods with nitrogen, fever