Key quantitative facts about basal metabolic rate.
What the evidence says
- Total daily energy expenditure comprises three components: resting metabolic rate (60-75%), thermic effect of feeding (~10%), and thermic effect of activity (15-30%)[1]
- Resting metabolic rate constitutes 60-75% of total daily energy expenditure — the largest component for most people, associated with maintenance of major body functions[1]
- Resting metabolic rate falls with age by more than body composition explains. A 2010 review relays a longitudinal study of German adults over 60, followed for 8 years: ”After adjusting for body composition, men had a 5% reduction in RMR per decade and women, a 3% reduction per decade”, and the researchers ”concluded that the decline in RMR was not entirely due to changes in body composition”. In the Baltimore Longitudinal Study of Aging, in men the ”rate of decline in RMR was faster at age 70–80 y than at age 40–50 y”[2]
- High-metabolic organs (brain, liver, heart, kidneys) account for ~60% of adult RMR despite comprising <6% of body weight; skeletal muscle comprises 40-50% of body weight but only 18-25% of resting energy expenditure[2]
- Skeletal muscle burns approximately 5.9 kcal per pound per day at rest (~6 kcal/lb/day); gaining 10 lbs of muscle would add roughly 60 calories/day to resting expenditure[3]