What is the difference between basal metabolic rate and resting metabolic rate?

Basal metabolic rate is measured under strict conditions — awake but fully rested, in a thermoneutral room, and in the post-absorptive (fasted) state. Resting metabolic rate is measured under less rigid conditions and is typically slightly higher, but the two terms are often used interchangeably in practice.

Why does basal metabolic rate differ so much between people?

The largest single determinant is fat-free (lean) mass, because muscle and organs are metabolically active tissue. Body size, age, and sex therefore account for much of the variation, with smaller additional influences from other physiological factors.

Basal Metabolic Rate and Total Daily Energy Expenditure

Basal metabolic rate (BMR) is the energy the body uses at complete rest to sustain vital functions, and it usually accounts for the largest share of total daily energy expenditure (TDEE) — the sum of all the energy a person spends in a day. Together they describe the expenditure side of energy balance and are the quantities nutrition science uses to estimate energy requirements.

Find emne med PaperMindSnartFind papers & topics

Tools & resources

Hent slides

Learn & explore

VideoSnart

Definition

Basal metabolic rate is the rate of energy expenditure of an awake person at physical and mental rest, in a thermoneutral environment and in the post-absorptive state; total daily energy expenditure is the total energy a person expends over 24 hours, comprising basal/resting metabolism, the thermic effect of food, and the energy cost of physical activity.

Scope

This topic defines BMR and the closely related resting metabolic rate, sets out the components of total daily energy expenditure, and explains how each is measured and what drives variation between people. It is reference physiology; it describes measurement and determinants rather than prescribing energy targets for any individual.

Core questions

What is included in basal metabolic rate and how does it differ from resting metabolic rate?
What are the components of total daily energy expenditure?
What determines how much energy a person expends at rest?
How is energy expenditure measured in the laboratory and in free-living people?

Key concepts

Basal metabolic rate
Resting metabolic rate / resting energy expenditure
Total daily energy expenditure
Thermic effect of food
Activity energy expenditure
Non-exercise activity thermogenesis (NEAT)
Fat-free mass as the main determinant of resting metabolism
Indirect calorimetry and doubly-labelled water

Mechanisms

Total daily energy expenditure is conventionally divided into three components: basal (or resting) metabolism, the thermic effect of food, and the energy cost of physical activity, the last of which includes both deliberate exercise and non-exercise activity thermogenesis from spontaneous movement and posture (Levine, 2002). Basal metabolism reflects the energy demands of the body's organs and tissues at rest; because metabolically active fat-free mass is its principal determinant, larger and more lean-mass-rich bodies have higher absolute BMR. Resting metabolism is measured by indirect calorimetry, which infers heat production from oxygen consumption and carbon dioxide output, while total expenditure in free-living people is measured with doubly-labelled water.

Clinical relevance

BMR and TDEE provide the conceptual basis for estimating energy requirements in nutrition assessment and for interpreting weight change in terms of energy balance. The topic is descriptive reference content on how expenditure is partitioned and measured and does not specify energy prescriptions for individuals.

Epidemiology

When body size and composition are taken into account, total daily energy expenditure is relatively stable across much of adulthood and is higher per unit mass in young children, with a decline in later life (Pontzer, 2021). Within individuals, deliberate weight loss lowers energy expenditure beyond what is expected from the change in body mass alone (Leibel, 1995; Rosenbaum, 2010).

History

Estimation of basal metabolism dates to early twentieth-century calorimetry, which related heat production to body surface area and underpinned the first prediction equations for energy needs. Indirect calorimetry made resting metabolism routinely measurable, and the validation of doubly-labelled water in humans in the late twentieth century allowed total expenditure to be quantified in everyday life, culminating in large multi-laboratory datasets describing expenditure across the lifespan (Pontzer, 2021).

Debates

How much does non-exercise activity thermogenesis contribute to expenditure and weight regulation?: Spontaneous, non-exercise movement varies widely between people and can account for a substantial share of daily activity energy; how much it adjusts in response to overfeeding or underfeeding, and how much it explains differences in weight gain, remains an active question.

Key figures

James A. Levine
Herman Pontzer
Rudolph Leibel
Michael Rosenbaum

Seminal works

leibel-1995
pontzer-2021

Frequently asked questions

What is the difference between basal metabolic rate and resting metabolic rate?: Basal metabolic rate is measured under strict conditions — awake but fully rested, in a thermoneutral room, and in the post-absorptive (fasted) state. Resting metabolic rate is measured under less rigid conditions and is typically slightly higher, but the two terms are often used interchangeably in practice.
Why does basal metabolic rate differ so much between people?: The largest single determinant is fat-free (lean) mass, because muscle and organs are metabolically active tissue. Body size, age, and sex therefore account for much of the variation, with smaller additional influences from other physiological factors.