Energy is released during digestion and stored in other molecules. It is then broken down to provide fuel to the body when needed.

Energy is used in three ways:

• Roughly 10% enables digestion
• About 20% fuels physical activity
• Around 70% support the basic functions of our organs and tissues. 

BMR is the number of calories you would need to survive. 

The official guidelines for how many calories the average person requires each day are based on only the body's most basic functions.

The MBR for women are 2000 calories and for men 2500 calories.  It is based on average weight, physical activity and muscle mass. 

If you are doing activities such as cycling the Tour de France, your body could use up to 9000 calories per day.  Pregnancy requires only slightly more calories than usual, and elderly people need fewer calories as they typically burn energy more gradually.

• The calorie counts on nutrition labels measure how much energy the food contains, not how much energy you can actually get out of it.
• Fibrous foods like whole-wheat take more energy to digest, meaning you'll get less energy from eating a 100 calorie serving than a 100 calorie serving of potato chips. 
• Different people might not get the same number of calories from eating the exact same food. It can vary based on enzyme levels, gut bacteria and intestine length.