Although the mass of every body includes the energy stored in its gravitational field, the only way to get a body to loose energy by gravity is by way of gravitational radiation. This is produced by accelerating the body, however, in order to get large mass losses, you need to accelerate the body enormously because gravity waves are so weak. The acceleration felt by two dense neutron stars orbiting around each other every minute at a distance of a few hundred kilometers is the most extreme acceleration known. It is not very effective in causing the bodies to loose much mass compared to the feeble mass lost by the electromagnetic radiation leaving their surfaces.