Your basal metabolic rate, or BMR, is...

the minimum calorific requirement needed to sustain life and to maintain bodily functions while your body is at rest. Another way to look at it is as the amount of energy your body would expend if you were to lie in bed all day.

It does not take into account any other daily activities that would expend calories such as working, walking, exercise, or any other daily chores.

BMR is the largest factor in determining an individualâ??s total metabolic rate. It is also important in determining how many calories a person needs in order to gain, lose, or maintain their current weight. A personâ??s BMR is determined by looking at a combination of genetic and environmental factors such as gender, genetics, age, weight, surface area of your body, body fat percentage, body temperature, external temperature, level of exercise.

Once you have an idea of your BMR, you can adjust your caloric intake and exercise level to reflect your particular fitness goals. Of course GymLobby will take all factors into account automatically once you create your goal.

Advanced readings

Basal metabolic rate (BMR) is the amount of energy expended while at rest in a neutrally temperate environment, in the post-absorptive state (meaning that the digestive system is inactive, which requires about twelve hours of fasting in humans). The release of energy in this state is sufficient only for the functioning of the vital organs, such as the heart, lungs, brain and the rest of the nervous system, liver, kidneys, sex organs, muscles and skin. BMR decreases with age and with the loss of lean body mass. Increased muscle mass can increase BMR. Aerobic fitness level, a product of cardiovascular exercise, while previously thought to have effect on basal or resting metabolic rate (RMR), has been shown in the 1990s not to correlate with BMR, when fat-free body mass was adjusted for (see following section "Aerobic vs. anaerobic exercise" for references). Illness, previously consumed food and beverages, environmental temperature, and stress levels can affect one's overall energy expenditure as well as one's BMR.

BMR is measured under very restrictive circumstances when a person is awake, but at complete rest. An accurate BMR measurement requires that the person's sympathetic nervous system not be stimulated. A more common and closely related measurement, used under less strict conditions, is resting metabolic rate (RMR).[1]

BMR and RMR are measured by gas analysis through either direct or indirect calorimetry, though a rough estimation can be acquired through an equation using age, sex, height, and weight. Studies of energy metabolism using both methods provide convincing evidence for the validity of the respiratory quotient (R.Q.), which measures the inherent composition and utilization of carbohydrates, fats and proteins as they are converted to energy substrate units that can be used by the body as energy.

Basal metabolic rate is usually by far the largest component of total caloric expenditure. However, the Harris-Benedict equations are only approximate and variation in BMR (reflecting varying body composition), in physical activity levels, and in energy expended in thermogenesis make it difficult to estimate the dietary consumption any particular individual needs in order to maintain body weight. 2000 kilocalories is often quoted but is no more than a guideline.

BMR estimation formulas

Several prediction equations exist. Historically most notable was Harris-Benedict equation, which was created in 1919.

The original equations from Harris and Benedict are:





where P is total heat production at complete rest, m is the weight, h is the stature (height), and a is the age, and with the difference in BMR for men and women being mainly due to differences in body weight. [2] For example, a 55 year old woman weighing 130 lb (59 kg) and 5 feet 6 inches (168 cm) tall would have a BMR of 1266 kcal per day or 52.8 kcal/h (61.3 watts).

It was the best prediction equation until recently, when MD Mifflin and ST St Jeor in 1990 created new equation:

, where s is +5 for males and â??161 for female. According to this formula, the woman in the example above has a BMR of 1208 kcal per day.

During the last 100 years, lifestyles have changed and a survey in 2005 showed it to be about 5% more accurate.

These formulae are based on body weight, which does not take into account the difference in metabolic activity between lean body mass and body fat. A more accurate formula is the Katch-McArdle formula based on lean body mass:

, where LBM is the lean body mass in kg.[3] According to this formula, if the woman in the example has a body fat percentage of 30%, her BMR would be 1262 kcal per day.

To calculate daily calorie needs, this BMR value is multiplied by a factor with a value between 1.2 and 1.9, depending on the person's activity level.

About 70% of a human's total energy expenditure is due to the basal life processes within the organs of the body (see table). About 20% of one's energy expenditure comes from physical activity and another 10% from thermogenesis, or digestion of food.[citation needed] All of these processes require an intake of oxygen along with coenzymes to provide energy for survival (usually from macronutrients like carbohydrates, fats, and proteins) and expel carbon dioxide, which is explained by the Krebs cycle.

What enables the Krebs cycle to perform metabolic changes to fats, carbohydrates, and proteins is energy which can be defined as the ability or capacity to do work. The breakdown of large molecules into smaller molecules associated with release of energy is catabolism. The building up process is termed anabolism. The breakdown of proteins into amino acids is an example of catabolism while the formation of proteins from amino acids is an anabolic process.