Basal metabolic rate (BMR), also called the resting metabolic rate, is the amount of energy needed to support the body's essential functions at rest, in a neutral, or non-stressful, environment. The body's essential functions include circulating blood, breathing, and producing body heat. Nonessential functions, such as digestion and standing are not included in the BMR calculation.
Both BMR and resting metabolic rate are usually expressed as daily rates of energy expenditure. BMR can utilize up to 70% of the calories that a person consumes in a day.
BMR calculations are increasingly being used by the public to formulate weight loss plans that proponents claim can be tailored to the individual's needs. It is also being investigated in its ability to estimate reproductive success and diabetes risk.
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The BMR estimates the minimum number of calories needed to maintain the body at rest. BMR does not take into account the calories needed for exercise, so it is not representative of the amount of calories burned per day. As individuals age or lose muscle mass, their BMR decreases, which means that less energy is needed to maintain the body's functions. Often, this occurrence is referred to as the metabolism "slowing down."
The primary organ responsible for regulating metabolism and the BMR is the hypothalamus. The hypothalamus regulates emotions, body temperature, appetite, weight, growth, sleep, electrolyte balance, among other functions.
The following details factors that may affect BMR.
Age: BMR decreases with age. After age 20, it drops about 2% per decade.
Body fat percentage: The lower the body fat percentage, the higher the BMR.
Body surface area: The greater the body surface area factor, the higher the BMR.
Diet: Starvation, eating disorders or serious abrupt calorie-reduction can dramatically reduce BMR up to 30%. Restrictive low-calorie weight loss diets may cause an individual's BMR to drop by as much as 20%.
Exercise: Since physical exercise burns calories, it influences body weight and helps raise an individual's BMR by building extra lean tissue (lean tissue is more metabolically demanding than fat tissue).
Gender: Men have a greater BMR due to their typically greater muscle mass and a lower body fat percentage than women.
Weight: BMR increases with increased lean weight.
Other factors: Other factors include: body temperature, genes, health, hormones, external temperature, medications, and glands/glandular function.