When the density is defined in proportion to energy contents, nutrient-dense foods such as fruits and vegetables are the opposite of energy-dense food (also called "empty calorie" food), such as alcohol and foods high in added sugar or processed cereals. Beyond its use to distinguish different "types" of food from each other, nutrient density allows comparison to be made for different examples or samples of the same kind of food. Nutrient density is correlated with soil quality and mineralization levels of the soil, although the relationship is complex and incorporates other dimensions.