Ask a Dietitian

As seen on BCTV

One of the most common questions I get asked from BCTV viewers is “how many calories should I eat to lose weight?”. Although I don’t recommend counting calories, I like to emphasize eating a certain number of servings from each food group, but I do calculate my clients’ needs to determine their servings. So, if you are interested in calculating how many calories your burn in a day here is how.

What is metabolism?

The rate at which your body burns energy for its basic functions to sustain life; organ functions, beating heart and breathing, is called the Resting Metabolic Rate (RMR) and makes up 70% of your metabolism. Your total energy expenditure for the day also includes the thermic effect of food (TEF) which accounts for 10% of the calories burned. This is the energy used to digest and absorb the nutrients in the food we eat. Physical activity accounts for 20-25% of the calories burned or more.

You can increase your metabolism by increasing your lean body mass (muscle) which burns up to 20 times more energy than fat mass. You can also boost metabolism by eating more often and higher fibre foods which will increase the Thermic Effect of Food. Regular exercise also boosts energy expenditure and metabolism.

To calculate your daily calories needs you need to first determine your Basal Metabolic Rate using the Harris Benedict equation. This formula takes into consideration your height, weight, age and gender but not body composition. Therefore this calculation would be inaccurate for those who are obese or extremely muscular.

Short method:
Not active: weight in lbs x 12
Active weight in lbs x 15

Ex: 140 lbs x 15 = 2100 kcal

Women: BMR = 655+ (4.35 x wt in lbs) + (4.7 x ht in inches) – (4.7 x age in yrs)
Ex: a woman 5’ 6”, 140 lbs, 35 yrs old, moderately active

BMR = 655 + (4.35 x 140) + (4.7 x 66) – (4.7 x 35)
BRM = 655 + 609 + 310.2 – 164.5
BMR = 1409.7

Men: BMR = 66 + (6.23 x wt in lbs) + (12.7 x ht in inches) – (6.8 x age in yrs)

Once you have the BMR then you need to multiply this by an activity factor

Sedentary – none or very little exercise = 1.2
Light activity for average of 2 days/week = 1.375
Moderate activity level exercising 4 days/week = 1.5
High activity levels exercise and sports more than 6 days per week = 1.7
Higher activity levels = 2.0

For the example above you would take an activity factor of 1.5

Daily calorie expenditure = 1409.7 x 1.5 = 2114.5 calories per day

If you want to lose weight you need to eat fewer calories than you burn so you can do a combination of increasing activity and reducing intake. It takes approximately 3500kcal deficit to lose 1 lb body fat so by subtracting 500kcal from your intake each day you would lose 1 lb per week.

The above individual should eat approximately 1600kcal per day to lose 1 lb per week.

Watch for the Eating for Energy segment every Tuesday on BCTV’s Noon News Hour!