Calories. Dieters think of them as the enemy, the part of food that prevents weight loss and deposits itself on the thighs. Food packages list calorie content per serving. You can track your calorie intake with computer software and counter books. Calorie information overload can turn eating into a numbers game instead of a pleasurable part of daily life. 

Kilojoules and calories both define the energy value of food. Calorie is still used in the USA to define energy, but Australia now uses kilojoule and you'll find this term shortened to kJ on food labels. The measurement of 'calories' signifies the amount of chemical energy that may be released as heat when food is metabolised. One calorie is equivalent to 4.2 kilojoules.

The balance between our energy intake versus the energy we expend is the main reason for weight loss or weight gain. Too many kJ eaten spells too much body fat on you. Too few kilojoules causes body fat loss.
Approximately two-thirds of your daily kJ needs are needed to just run your body as though you were asleep - to keep the blood pumping, your heart beating, your brain and nerves firing, your lungs breathing, and for the repair and maintenance of all your body's cells. This is called the "basal metabolic rate".

Everyone needs calories
The truth is everyone needs some calories every day. Unless you are a highly trained athlete, your biggest daily calorie cost is something called Resting Metabolic Rate, or RMR, the calories you need just to exist. Breathing, heart beat, cell metabolism, kidney function and even thinking and dreaming use calories. Muscle cells use calories even when at rest. Eating and digesting food, standing, sitting, talking and surfing the Internet all burn calories beyond the basic RMR requirement.

What’s a calorie?
Calorie is a term for the energy content of food. Some food is very dense in energy, like butter or vegetable oil. Some has much less, like celery or cucumbers. . Unlike cars, humans don’t have limited fuel tanks. We have expandable fuel tanks called fat cells. Also unlike cars, we can ramp up our daily calorie use by adding physical activity.

Measuring individual calorie use
It’s not easy to come up with an accurate number for your individual calorie needs. There are mathematical equations that attempt to estimate calorie needs based on simple body measurements, such as gender, age, height and weight. But equations have limitations. Research shows that most are off by anywhere from 5% to 25% when used to predict a person’s basic calorie requirement. If you are trying to plan a reduced calorie diet, it’s not helpful if the equation overestimates your basic needs by 25%.

Move more to burn more
Physical activity not only burns calories, but helps you burn extra calories all day, even when you’re not exercising. Active people have more muscle than sedentary people. Muscle tissue has higher calorie needs even at rest than fat tissue. This is an excellent reason to include exercise in your daily routine.
Those who exercise, or have a job requiring physical energy, have a higher basal metabolic rate and thus burn more kilojoules. For example a sedentary office worker may use about 9000kj per day, a manual worker lifting materials may burn approximately 12500kj per day, and a labourer or elite athlete may use up to 17000kj per day.

To know your calorie intake is to monitor your weight. If your weight is stable, you’re eating the same amount of calories you burn. If you want to lose weight - you have to eat less than that amount or burn more with exercise.