The basal metabolic rate (BMR) is the amount of energy needed while resting in a temperate environment when the digestive system is inactive. It is the equivalent of figuring out how much gas an idle car consumes while parked. In such a state, energy will be used only to maintain vital organs, which include the heart, brain, kidneys, nervous system, intestines, liver, lungs, sex organs, muscles, and skin.

BMR Variables

Several factors influence BMR:

• Muscle Mass: The more muscle mass, the higher the BMR. Anaerobic exercises like weight-lifting build muscle mass, increasing resting energy consumption.
• Age: The more elderly an individual, the lower their BMR, as metabolic processes slow down with age.
• Genetics: Hereditary traits passed down from ancestors influence BMR.
• Weather: Cold environments raise BMR because of energy required to maintain body temperature. BMR increases approximately 7% for every increase of 1.36°F in body temperature.
• Diet: Small, routinely dispersed meals increase BMR. Starvation can reduce BMR by as much as 30%.
• Pregnancy: Ensuring the livelihood of a separate fetus internally increases BMR.
• Supplements: Certain supplements or drugs like caffeine can raise BMR.

Activity Level Multipliers

The daily caloric need is the BMR value multiplied by a factor with a value between 1.2 and 2.0, depending on activity level:

Limitations & Accuracy

A 2005 meta-analysis study on BMR showed that when controlling all factors of metabolic rate, there is still a 26% unknown variance between people. Essentially, an average person eating an average diet will likely have expected BMR values, but there are factors that are still not understood that determines BMR precisely.

Online BMR tests with rigid formulas are not the most accurate method of determining an individual's BMR. It is better to consult a certified specialist or measure BMR through a calorimetry device. However, BMR calculations can aid in laying down the foundations for health and fitness goals.

Sources & References