How to Calculate Your Metabolic Rate
The most basic way to estimate resting metabolic rate, RMR, is to use the Mifflin-St Jeor equation. This equation, derived in 1990, came about from measuring indirect calorimetry in human subjects. As far as energy expenditure equations go, it’s currently the most accurate, although it has limitations is normally used as a starting-off point.
Mifflin-St Jeor ousted the previously popular Harris-Benedict equation, which was created in 1919 and overestimates RMR by 5 percent.
The Mifflin-St Jeor Equation is as follows, for ages 19–78:
Men: 10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) + 5
Women: 10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) – 161
To give yourself an idea of the total calories you’re burning in a day, you take that number and multiply it by your personal activity factor:
Sedentary = 1.2
Lightly active = 1.375
Moderately active = 1.550
Very active = 1.725
Extra active = 1.9
If you’re like most Americans, you need to convert your weight and height to metric units before entering into the equation:
For your weight in kilograms, divide your weight in pounds by 2.2: For example, if you weigh 165 pounds, divide by 2.2 to get 75 kg.
For your height in centimeters, multiply your height in inches by 2.54: If you’re 5’5, or 65 inches, multiply by 2.54 to get 165.1 cm.
For example, if you’re a 45-year-old woman, you’d calculate your RMR like this:
(10 x 75kg) + (6.25 x 165.1) – (5 x 45) – 161 = 750 + 1,032 – 225 – 161 = 1,396 calories
Then, you’d multiply by your activity factor, which takes into account your day-to-day movement and planned exercise:
If you’re sedentary (you work at a desk job and do very little exercise or housework): 1,396 x 1.2 = 1,675 calories
If you’re lightly active (you go for long walks 1–3 days per week or do housework like cleaning and gardening): 1,396 x 1.375 = 1,920 calories
If you’re moderately active (you’re moving most of the day and/or exercise with a moderate amount of effort 3–5 days of the week): 1,396 x 1.550 = 2,164 calories
If you’re very active (you’re vigorously exercising or playing sports most days): 1,396 x 1.725 = 2,408 calories
If you’re extra active (vigorous exercise or sports 6–7 days of the week plus a job which requires physical exertion): 1,396 x 1.9 = 2,652 calories
Your turn: What is your total energy expenditure? _______
As you can see, the more active you are, the higher your metabolic rate, or TEE, and the more calories you need. That’s why exercise is such a key component of the maximizing your metabolism plan. Even better, the more muscle mass you build, the higher your RMR will be.
Unfortunately, unless you’re an elite athlete, simply adding exercise won’t automatically translate into an increased metabolic rate. Research published July 2012 in the journal PLos One examined the Hadza people from Tanzania who are hunter-gatherers. You’d think because they’re always active, walking miles and miles every day, that their metabolic rates would be higher.
This study found that although their activity was greater than the average Westerner, their metabolic rates were not.
If you eat more than you need, even with additional exercise you can still pack on the pounds. Also, it’s possible your body gets used to the type of activity you do on a daily basis, which is why it’s important to mix up your exercise routine with strength and interval exercises to keep your body guessing.
The Mifflin-St Jeor equation takes into account variables that affect metabolic rate across the board. However, if you’re taller, heavier, and more active, you’ll burn more calories than a shorter, thinner, less active person. The older you are, the fewer calories you burn due to decrease in muscle over time. And if you’re a man, you burn more calories at rest than a woman due to a greater percentage of muscle mass.
What the Mifflin-St Jeor equation fails to take into account is variations in individual lifestyle and body composition, meaning you might have different caloric needs than your female friend who is also 5'5", 165 pounds, 45 years old and goes to the same exercise class as you. However, it’s a great jumping-off point to start understanding your daily calorie burn.