Calculating Your Caloric Needs
For a person whose body mass index (BMI) is in the normal range (i.e. between 18.5 and 25), staying at their current weight is recommended. This requires eating and burning the same number of calories. When people need to lose weight, they must create an energy (calorie) imbalance by eating fewer calories than they burn.
So to know how many calories a person needs, you start by estimating the number of calories they burn each day, that is, their total energy expenditure (TEE).
Each individual has his or her own basic energy expenditure called basic metabolic rate or resting metabolic rate, meaning the energy the body uses to ensure vital functions (maintaining body temperature, thinking, keep the heart beating). The fundamental rule to observe: make sure you eat at least this number of calories!
- Calculate your basic metabolic rate (BMR):
Here’s a simple formula for calculating your BMR (adapted from Mifflin-St. Jeor):
Women: 10 x weight (kg)* + 6.25 x height (cm) – 5 x age (y) – 161
Men: 10 x weight (kg)* + 6.25 x height (cm) – 5 x age (y) + 5
*The weight used in the formula should be your adjusted weight if your BMI is higher than 30:
1) Adjusted weight is calculated as follows: Ideal weight + 0.4 x (actual weight – ideal weight)
2) Ideal weight is calculated using the formula that corresponds to your gender:
Men = 50 kg + (0.92 x [height in cm – 152])
Women = 45 kg + 0.92 x [height in cm – 152])
- Determine your level of physical activity (LPA):
Then, the result (number of calories) obtained for the basic metabolic rate (BMR) has to be multiplied by a physical activity factor (LPA).
Daily LPA is determined as follows:
Basic activities (general movement, chores, light office work, etc.)
+ 30-60 minutes or more of moderate intensity activity (brisk walking, light jogging, recreational sports, cycling at a moderate speed, aerobics, etc.
+ 60 minutes or more of moderate intensity activity
Or 30-60 minutes of vigorous activity (running, CrossFit-type training, competitive swimming, etc.)
+ about 60 minutes of moderate intensity activities AND at least 60 minutes of vigorous activity, OR 180 minutes of moderate intensity activity.
- Calculate your total energy expenditure (TEE):
BMR X LPA = TEE
Once you know what your LPA is, that is, the result of multiplying your BMR by your LPA, you will know what your calorie needs are (the number of calories you should eat) for maintaining your current weight.
Determine the number of calories you should eat if you want to lose weight
To lose about one pound a week, you have to cut back 500 calories a day from this number to generate an overall deficit of 3500 kcal a week.
Losing one to two pounds a week is considered as healthy.
The above are theoretical calculations. In practice though, appetite varies from one day to the next depending on your daily activities and the energy required for recovery. So it’s important to tune in (or learn to tune in) to your hunger and fullness signals.
Marie-Ève Nadeau Dt.P.
Note: The formulas used are from the book Take charge of your health and fitness with the Transform program