Oil loss but oil is not leaking?

Oil loss but oil is not leaking?
oil is being burned threw the piston oil rings,valve gides ,sometimesits as sample as a pcv valve that is sucking to much.high mile carswill use more oil .Try thicker oil.if your using 5/30 oil.move it up to10/30,10/30 change to 10/40,10/40 change to 20/50.