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FREE BMR/ RMR CALCULATOR
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WHAT IS BMR/ RMR?
About Basal Metabolic Rate

Basal metabolic rate (BMR) is the amount of energy expended while at rest in a neutrally temperate environment.  It requires inactivity from digestion, so you would need fast for at least 12 hours. 

 

Then using special equipment, the energy needed to maintain vital functions in your body, like breathing, kidney function, and heart rate, are measured in calories per unit of time (usually 24 hours).  The picture on the left is what the test for BMR looks like. 

 

There are several formulas for calculating BMR. The Mifflin-St Jeor equation is more likely than the other equations to estimate BMR to within 10% BMR (1). 

The Mifflin-St Jeor Equation:

For men: BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) + 5

For women: BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) – 161

To determine your weight in kilograms, divide your weight in pounds by 2.2.

For example, if you weigh 175 lbs: 175 ÷ 2.2 = 79.54 kilograms. 

 

To determine your height in centimeters, multiply your height in inches by 2.54.

For example, if you are 5 feet 2 inches tall: 60 inches + 2 inches = 62 inches tall x 2.54 = 157.48 centimeters.

In this equation, weight must be in kilograms, height in centimeters and age in years. 

 

 

 

 

 

 

 

 

Variables affecting BMR:

There are limits to all equations that attempt to calculate BMR because many variables play into it.  Your age, hormones, nutritional status, body composition, body temperature, weight and genetics all affect BMR.

 

Age is one of the most important factors of changes in energy metabolism. The basal metabolic rate decreases almost linearly with age (2).  As you age your BMR will decrease.

 

Hormone levels, especially thyroid hormones, are important determinants of overall energy expenditure and the BMR (3).

 

Low nutritional status or semi-starvation will reduce your BMR.  Your body adapts to this kind stress by conserving energy (4).    In "Very Low Calorie Diets (VLCD)" this can be as much at 23% (5).

 

Body composition or the percentage of fat mass to muscle mass will affect BMR.  Muscle is more metabolically active and results in a higher BMR.  Men typically have a greater percentage of muscle mass compaired to woman and consequently, have a higher BMR.

 

Increases in body temperature due to sickness or hot climates will increase your BMR.

 

Body weight is directly related to BMR.  The more you weight the higher your BMR.  During pregnancy increases to BMR is significantly due to weight gain by 40% (6).

 

Genetics, while not fully understood, can affect BMR.  Some people were just born with a higher BMR, while other people were born with a lower one.

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