A feeder for a machine for canning tuna and similar food products includes a feeding device with conveyor belts. The feeding device is suitable to feed tuna loins towards the conveyor belt of the canning machine and to shape the loins into loins having a set thickness. An outlet mouth is located at the end of the belts, together with a knife adjacent to the mouth and suitable to separate the portion of loin projecting through the latter. A mobile wall located opposite the outlet mouth is also provided, as well as a mobile shovel suitable to move the newly formed tuna pat perpendicularly in the direction of motion of the conveyor belt of the canning machine.