Calculating Your Weekly Calorie Expenditure and Requirements

     An individual's daily calorie expenditure is dependent on 3 main factors. Firstly, it will depend on an individual's basal metabolic rate (BMR), which represents the number of calories burned at rest due to metabolic functions within the body. This can be approximated as 25 calories per kilogram of body mass, per day.

The second factor to be considered is an individual's lifestyle and general activity levels (Activity Factor, F). People who are generally more active throughout the day will consume more calories than an inactive person. Below is an approximation of the additional calories used due to lifestyle activity. This is only an approximation as it is difficult to clearly define levels of activity in this manner:

Sedentary Lifestyle (=BMR x 120 %) - Typical characteristics include having a desk-based job (office worker), driving to work, taking the elevator and not the stairs, etc.

Moderately Active Lifestyle (=BMR x 150%) - Typical characteristics include having a job requiring prolonged periods of standing (nurse or factory worker), walking or cycling to work, taking stairs not elevators, etc.

Very Active Lifestyle (=BMR x 175%) - Typical characteristics include having a manual job (labouring or exercise teacher), walking or cycling to work, taking stairs not elevators, etc.

The third and final factor for consideration relates to formal exercise. During formal exercise there is the potential to expend many calories. The exact quantity will depend on the type of activity, the participant's weight and the intensity. Most cardiovascular machines in a health centre will calculate the calories expelled based on a person's weight and the intensity at which they are exercising.

To approximate your weekly calorie expenditure, you can enter your own information into the equations below:

Firstly, calculate you BMR = Weight (kg) x 25 =

Next, include calories relating to your activity level = BMR x F =
(Sedentary Lifestyle = BMR x 1.2, Moderately Active Lifestyle = BMR x 1.5, Very Active Lifestyle = BMR x 1.75)

Now multiply by 7 for days of the week = BMR x Activity Factor x 7 =

Finally, add calories expended during formal exercise during the week = BMR x Activity Factor x 7 + Calories Expended During Exercise =

This gives you the total quantity of calories expended in a given week.

In order to balance your calories for a given week, simply subtract the number of calories expelled from the number of calories taken in:

Weekly Calorie Intake - Calorie Expenditure = Net Weekly Calories

If this result is negative, your weight is likely to decrease and if it is positive, your weight is likely to increase. As an approximation, in order to reduce your body mass by 1kg, you have to expend 7000 calories more than you intake. Conversely, to gain 1kg, you have to intake 7000 calories more than you expend.

An individual with weight loss goals should aim to lose between 0.5 and 1 kg body weight per week. Aiming to lose more could result in a slowing of the metabolism, as the body goes into a state of starvation. Therefore, a weekly calorie deficit between 3500 and 7000 kg is required (net calories = -3500 to -7000). An individual with weight gain goals, aiming to gain between 0.5 and 1 kg body weight per week will require a weekly calorie surplus between 3500 and 7000 (net calories = 3500 to 7000).

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