Q: "I was wondering roughly how much energy a person uses each day, simply maintaining all bodily functions. So, in other words, what’s the minimum number of calories required for someone to live?"
A: The energy needed to maintain all bodily functions to keep the body alive and healthy is known as the Basal Metabolic Rate (BMR). In most people the BMR is somewhere between 50–70% of daily kilojoule needs. An 80kg man aged between 31–50 years has a BMR of 7500kJ (1785 calories) per day. A woman of the same age weighing 64kg has a BMR of 5700kJ (1360 calories) per day.