Candy is considered a source of empty calories, because it provides little or no nutritional value beyond food energy. At the start of the 20th century, when undernutrition was a serious problem, especially among poor and working-class people, and when nutrition science was a new field, the high calorie content was promoted as a virtue. Researchers suggested that candy, especially candy made with milk and nuts, was a low-cost alternative to normal meals. To get the food energy necessary for a day of labor, candy might cost half as much as eggs. During the 1920s and 1930s, candy bars selling for five cents were often marketed as replacements for lunch.