Calorie and body weight basics
- units of energy your body uses to fuel its functions and activities
- created from proteins, fats and carbohydrates found in our foods and beverages
- necessary for basic body functions like keeping the heart, brain and lungs functioning (also known as basal metabolism)
- essential to fuel activity – from the smallest hand gesture to a 5-mile run
The number of calories we need each day depends on how much we weigh, how much muscle mass we have and how active we are.
If you consume more calories than your body needs, those extra calories will be stored as fat.
If you consume less calories than your body needs, your previously stored calories (fat) will be used to supply additional energy.
One pound = approximately 3,500 calories
What is Energy?
Kilojoules and calories are both units of measure of energy, in a similar way to how kilometres and miles both measure distance.
4.184 kilojoules (kJ) = 4,184 joules = 1 Calorie (Cal) = 1 kilocalorie = 1,000 calories
Energy is consumed through foods we eat (carbohydrates, fat and protein) i.e. "energy in", and it is also expended by our body to fuel its functions and activities i.e. "energy out". The amount of energy we need each day depends on how much we weigh, how much muscle mass we have, and how active we are.
Energy balance is the relationship between "energy in" and "energy out". This relationship, which is defined by the laws of thermodynamics, dictates whether weight is lost, gained, or remains the same.
Positive Energy Balance: This occurs when you consume more kilojoules or calories than your body needs. Negative Energy Balance: This occurs when you consume less kilojoules or calories than your body needs.
To Lose Weight
By cutting down 500 calories (2090 kilojoules) per day, you will cut a total of 3,500 calories (14, 630 kilojoules) per week – resulting in the loss of 1 kilogram (2.2 pounds) of body fat. But never consume fewer than 1,200 calories (5016 kilojoules) per day.*
If you want to lose more than this, you will need to either reduce your energy intake further,* or increase the amount of energy you burn with exercise.
To Maintain Weight
Balance your "energy in" and "energy out".
If you are a woman
You will need about 12 calories for every pound of body weight (A 150-lb. woman needs about 1,800 calories a day.)
If you are a man:
You will need about 14 calories for every pound of body weight. (A 200-pound man needs about 2,800 calories a day.)
*Source: Dietary Guidelines for Americans, 2005. U.S. Department of Health and Human Services, U.S. Department of Agriculture (USDA)
**Source: Dietary Guidelines for Americans, 2005. U.S. Department of Health and Human Services, U.S. Department of Agriculture