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    BMr
    Home > Parameters

    BMr

    Basal metabolic rate: components of daily energy expenditure, the Mifflin–St Jeor equation and factors that change BMR.

    Basal metabolic rate (BMR) is the energy the body uses at complete rest to keep itself alive: breathing, blood circulation, brain and kidney work, maintaining body temperature and renewing cells. It is measured in the morning after a night's sleep, after 10–12 hours of fasting, lying still in a comfortably warm room. In most people BMR makes up the largest part (about 60–70%) of daily energy expenditure. It depends mainly on lean (fat-free) body mass, and also on sex, age, hormones and genetics.

    MetabolismEnergy balanceNutrition
    Unitkcal/day (1 kcal = 4.184 kJ)
    Reference methodindirect calorimetry
    Common estimateMifflin–St Jeor equation
    Share of daily expenditure≈ 60–70%
    Components of total daily energy expenditure in a typical sedentary adult: basal metabolic rate about 60 to 70 percent, thermic effect of food about 10 percent, physical activity the remainder Total daily energy expenditure Basal metabolism ≈ 60–70% ≈ 10% Activity organs, temperature, cell renewal digesting food movement, exercise The activity share varies most: from about 15% in sedentary people to 40% or more in very active people.
    Figure 1. Approximate components of daily energy expenditure in a sedentary adult.

    Estimating BMR

    The Mifflin–St Jeor equation, derived from indirect calorimetry in about 500 adults, predicts resting energy expenditure more accurately than the older Harris–Benedict equation, which overestimated it by about 5%:

    Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5

    Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161

    Example: a 40-year-old man, 80 kg, 180 cm: 800 + 1125 − 200 + 5 = 1730 kcal/day. Equations can be off by 10% or more in an individual, especially with obesity, low muscle mass or illness; then measurement is preferred.

    What changes BMR

    Lower BMR

    Older age, less muscle, hypothyroidism, prolonged dieting or starvation (adaptive slowing), adrenal or pituitary insufficiency.

    Higher BMR

    More muscle, hyperthyroidism, fever (≈ 10–13% per °C), infections, burns, trauma and surgery, cancer, pregnancy and breastfeeding, some medicines and stimulants.

    Why it matters

    BMR is the starting point for planning nutrition: multiplied by an activity factor it gives daily energy needs. Unexplained weight loss with a high metabolic rate, or weight gain with a low one, may indicate thyroid disease and needs a doctor's assessment.

    References

    1. Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–247. doi:10.1093/ajcn/51.2.241
    2. FAO/WHO/UNU. Human energy requirements. Report of a Joint FAO/WHO/UNU Expert Consultation. FAO Food and Nutrition Technical Report Series 1. Rome: FAO; 2004. fao.org/3/y5686e

    This article is for general information and does not replace a consultation with a doctor. Measurements must be interpreted by a physician together with symptoms and other tests.

    Published on 2 June 2019