Whats a calorie

A calorie ('c') is a unit of measurement of the energy contained in food. One Calorie ('C', not to be confused with '°C' as in 'degrees Celsius') is equal to 1kcal, or 1,000 calories (or 4,184 joules). One calorie (1c, or 0.001kcal) ) is the amount of energy it takes to heat 1g of water by one degree Celsius (or by one degree Kelvin,°K); more specifically, from 14.5 °C to 15.5 °C (or 287.65 °K to 288.65 °K) as the thermal capacity of water is dependent upon temperature.

Daily minimum energy requirements vary from person to person depending upon their sex, build, age, and level of physical activity. On average, the recommended daily intake for men is 2,500-3,300kcal per day, and for women, 1,500-2,500 per day.

Most of that energy is required just to function (ie- heart beat, maintaining body temperature, etc.); this is referred to as your Basal Metabolic Rate. Failing to consume the required energy to cover your BMR plus any physical activity you participate in, will result in the increased consumption of energy stores in the body, leading to weight loss. Consuming more calories than you require will lead to weight gain as the body stores energy for later use in the form of fat.

Continually failing to supply energy requirements will eventually lead to starvation. Once the body runs out of energy stores, it moves on to the muscles, bones, and ultimately, the internal organs, fighting to supply the required energy to keep you alive. Extreme or continual starvation will lead eventually to death.