Microwaves, as electromagnetic waves, do not lose energy as they heat food. Instead, they transfer their energy to the water molecules present in the food, causing them to vibrate and generate heat. This process is known as dielectric heating.
When microwaves interact with food, they are absorbed by the water molecules, as well as other polar molecules such as fats and sugars. These molecules have positive and negative charges that can align with the alternating electric field of the microwave radiation, causing them to rapidly rotate and collide with other molecules, thus generating heat.
The energy carried by the microwave radiation is effectively converted into thermal energy within the food, resulting in the heating of the food itself. Therefore, microwaves do not lose energy in the process of heating food but rather transfer their energy to the molecules within the food, causing them to vibrate and generate heat.
It's worth noting that some energy can be lost due to inefficiencies in the microwave oven itself, such as heat dissipation from electrical components or radiation leakage, but this is not directly related to the heating process caused by microwaves interacting with food.