Practically Instant The phenomenon of heating food without affecting the material covering it is possible because microwaves are quickly absorbed by water, fats, and sugars. When these substances absorb the microwaves, their atoms begin to accelerate, creating heat. Since foods contain water, fats, and sugars, they can be heated easily using microwaves. Most plastics, glass, and clothing materials, however, do not absorb microwaves. This is why containers tend to remain cool in microwave ovens while the food inside them is heated. People who simply don't have the time to create meals in a conventional oven can still enjoy cooked meals at home. Grocery stores offer "frozen dinners," which usually consist of pasta or meat and some vegetables. These dinners, which require up to an hour to cook on a regular stove, can be served in minutes when a microwave oven is used. In addition, food that is prepared in a microwave oven is usually healthier, since the cholesterol-heavy butter and oils that are often used during stove preparation aren't needed. Also, food that is exposed to long periods of heat can lose precious nutrients, whereas food cooked quickly in a microwave oven can retain most of its important nutritional value.