This article is from the Running FAQ, by Ozzie Gontang with numerous contributions by others.
This term refers to the quantity of nutrients in a food for its
accompanying caloric(energy) value. A twinkie contains much energy but few
vitamins and minerals so has a low nutrient density. Liver, on the other
hand, has a moderate amount of calories but is rich in vitamins and
minerals and is considered a high nutrient density food.
Basically, one must meet his/her nutrient requirements within the
constraints of his/her energy demands. Persons with a low daily activity
level have a low energy demand and in order to maintain their body weight
must eat high nutrient density foods. As already mentioned, a *runner* has
an increased energy demand but no significant increase in nutrient
requirements. Because of this he/she can eat foods with a lower nutrient
density than the average person. This means that a *runner* can be less
choosy about the foods that are eaten provided he/she realizes his/her
specific nutrient and energy requirements that must be met.