Food eaten by human and respired to generate metabolic energy. In any energy conversion, some energy is always converted into heat. Ultimately, all energy can be turned into heat. Since heat is a form of energy, we measure it by its capacity to do work. The calorie is one unit of heat measurement.
Temperature measures the intensity or degree of hotness of an object.
Physically, it is the average speed of random molecular motion of a substance. We sense temperatures by detecting the average speed of random motion exerted by the molecules of a substance on our skin. Rub your hands together. It will increase the random motion of skin molecules, and you will detect that your hand's temperature rises. Compare freezing and boiling point of Fahrenheit and Celcius.