My definition of authentic body:

Our body’s natural shape and size when we are not overeating, undereating, dieting or controlling ourselves with exercise or restriction. This is our bodies when we’re moving in fun and inspired ways, honoring our body’s signals and eating food we love. This is our “true” body which is largely determined by genetics. It's the body we have when we treat ourselves like something we treasure. It’s a body we naturally love simply because it's ours.