Lack of water protects the food. Water in the insect makes them easy to kill. The foods do not contain radioactivity. A type of electromagnetic radiation. Same energy band as radar.
Water is a dipole.
That means that water has a portion of the molecule that is more negative and a portion that is more positive than neutral molecules. When placed in a magnetic field the water will align with the filed. Microwaves cause a magnetic field that rapidly changes its orientation. The water molecules align with the field, as the field changes, the water attempts to change its position to align with the field. The magnetic field changes very quickly, so the water molecules must also move very quickly.