The health of the general population in previous eras was terrible, but it was especially bad for the lower classes. In the eighteenth century, for example, chronic malnutrition was so severe that the bottom 20 percent of the English income distribution lacked the energy for regular work. From the Elizabethan age to the end of the nineteenth century, one-fifth of the potential English labor force lived out their brief lives as paupers and beggars. These potential workers were excluded from the labor force not because of an inadequate demand for labor, as was the case during the Great Depression of the 1930s, but because they lacked entitlements to food. The situation in France and the rest of Western Europe was even worse than in England. Prior to the twentieth century, chronic malnutrition was the fate of the majority of the population.

The problem was not only that most of the population of Western Europe lacked adequate amounts of energy for work but also that their food supply was typically too small to allow for their proper physiological development. Energy available for work is a residual. It is the difference between the food metabolized (chemically transformed so that its energy is available for use by the body) and the energy that the body requires for baseline maintenance. Baseline maintenance has two components. The larger component, the basal metabolic rate (or BMR), accounts for about four-fifths of baseline maintenance. BMR is the amount of energy needed to maintain body temperature and to keep the heart and other vital organs functioning when the body is completely at rest. The other 20 percent of baseline maintenance is the energy needed to digest food and for vital hygiene (defecating, urinating, washing). It does not include the energy needed to prepare a meal or to clean the kitchen afterward.