Fisting mostly has the same risks as fingering. In addition, due to the size of the object being inserted, there may be an increased risk of tearing. This, in turn, could increase the risk of STD transmission.
If you are engaging in fisting, it is a good idea to use a latex or nitrile glove to protect both you and your partner. If you have long fingernails, you can pad them with cotton balls and wrap them inside the glove to reduce the risk of tearing it. Gloves also reduce the risk of scratching your partner.
Fisting is not a sexual activity that everyone wants to do, or feels safe participating in. As with all sexual activities, it is not something you should try to pressure your partner into if they are uncomfortable with the idea or unready.
People of all sexual orientations engage in both vaginal fisting and anal fisting.