Calories or Joules are heat energy units used in Thermodynamic physics. Listed below are some references to understand how they are applied to food. The Bioimis program does not consider these units in the food valid, rather it considers the metabolic-hormonal response to food.
Here are the baseline studies:
Patrizia Cappelli, Anna Vannucchi., Principles of food science third edition, Zanichelli Editor, Bologna 2008.
FAO - Food and Agriculture Organization, Human energy requirements. Report of a Joint FAO/WHO/UNU Expert Consultation. (Roma, 17-24 ottobre 2001).