Basal metabolic rate and calorie consumption
The math is quite simple! If we eat more food than you burn, we gain weight. In the opposite case, we lose weight. How many calories we burn each day is calculated from our basal metabolic rate and an activity factor. The actual calorie consumption is called power consumption.
How is basal metabolic rate calculated?
Basal metabolic rate is the energy the body consumes at rest to maintain body temperature and basic organ activity.
Basal metabolic rate depends on sex, age, body weight, hormone status, genes and muscle mass. Women have a lower basal metabolic rate than men because of their lower muscle mass at the same weight. For this reason, the value of women's body weight is reduced by another 10 percent for 24 hours a day.
Women: Body weight (kg) x 24 hours - 10 % = basal metabolic rate (cal)
Men: body weight (kg) x 24 hours = basal metabolic rate (cal)
Example woman:
A woman weighs 80 kilograms (176 pounds)
80 x 24 = 1,920 - 192 = 1,728 cal basal metabolic rate
Example man:
A man weighs 80 kilograms (176 pounds)
80 x 24 = 1,920 cal basal metabolic rate
Basal metabolic rate decreases with age
From the age of 30, approximately one percent of muscle mass is converted into fat every year. This means that the basal metabolic rate decreases with the same weight because the proportion of muscle mass has decreased.
For a 50-year-old woman, the calculation is as follows:
80 kilograms (176 pounds) x 24 hours = 1,920 - 192 (10%) = 1,728 - 346 (20%) = 1,382 cal basal metabolic rate
Here we also find the explanation for why we grow fatter with age, although we have not changed our eating habits. The only way to be able to eat as much as we did at a young age and still not gain weight is to exercise in a way that does not lead to muscle loss.
Physical activity metabolic rate
The actual calorie consumption per day depends on our physical activity at work and at leisure. An activity factor, known as PAL (physical activity level), has been defined for activity intensity.
The power consumption is calculated by multiplying the basal metabolic rate by the activity factor (PAL value).
The following values apply:
| Activity | PAL value | Examples |
|---|---|---|
| Sitting or lying | 1,2 | elderly people |
| Sitting, some leisure activity | 1,4 | office clerk |
| Standing and walking | 1,7 | housewife, salesperson, handyperson |
| Heavy physical work | 2,0 | construction worker, competitive athlete |
Let's get back to our example:
A 50-year-old woman with a weight of 80 kilograms (176 pounds) has a basal metabolic rate of 1,382 cal. Let's say she works in an office and works out very little, so she has an activity factor of 1.4.
1,382 x 1.4 = 1,935 cal. Her physical activity metaboloc rate is 1,935 cal.