There is, in fact, no difference in meaning between preventive and preventative. Some, including William Safire in a 1993 On Language column, have suggested using preventive as an adjective and preventative as a noun, but both forms of the word have alternated freely as adjective and noun since they entered the language in the 17th century. Despite their introduction into English at roughly the same time (the Oxford English Dictionary dates preventive back to 1626 and preventative to 1655), preventive has won out as the preferred version.
Diabetes is a number of diseases that involve problems with the hormone insulin. Normally, the pancreas (an organ behind the stomach) releases insulin to help your body store and use the sugar and fat from the food you eat. Diabetes can occur when the pancreas produces very little or no insulin, or when the body does not respond appropriately to insulin. As yet, there is no cure. People with diabetes need to manage their disease to stay healthy.