The acetyl Co-A produced by mitochondrial P-oxidation of fatty acids enters the Krebs cycle to produce energy, but that is not the only fate of acetyl Co-A. In liver mitochondria, some acetyl Co-A is converted to acetoacetate, β− hydroxy butyrate and acetone, collective called ketone bodies, which are transported to other tissues (e.g., brain, muscle or heart) where they are converted back to acetyl Co-A to serve as an energy source.