Abstract
The joule (J) has been the only scientific unit of energy included in the International System of Units(SI) since the 1950s; nevertheless, the calorie (cal) is still commonly used as a unit of energy in the field of nutrition and related areas. The unit used in any particular academic paper depends on the editorial policy of the publishing journal, so there is a great deal of inconsistency among academic papers in this field. We investigated in the present study the policy on energy units in 20 noted international journals and consider the reasons for each journal’s policy. We identified five types of journal policy after contacting the journals and looking up ‘energy intake’ in PubMed. Two journals have exclusively adopted kJ (MJ), three require kJ but also permit authors to provide kcal in parentheses where appropriate, one allows the use of kcal but also requires kJ in parentheses when kcal is used, twelve allow both kcal and kJ, and two have exclusively adopted kcal. Despite the general prevalence of using SI units in the modern world, kcal remains widely recognized as a unit of energy in the field of nutrition. We suggest four possible reasons for this. First, J did not originally refer to heat or potential energy. Second, the potential energy of food is measured by burning it and measuring the resulting increase in the temperature of water in a process directly related to the definition of cal. Third, cal is easy for the general public to understand. Fourth, cal is the unit most commonly used by the general public in daily life, and therefore must be adopted in field studies.
