Basal metabolic rate (or resting energy expenditure)
The number of calories the body burns at rest to maintain vital functions (breathing, circulation, protein synthesis and so on), independent of physical activity.
Basal metabolic rate (BMR) accounts for about 60-70% of total energy expenditure in a sedentary person. It varies with:
- Weight and body composition: more muscle = higher BMR
- Age: falls by about 2-3% per decade after 20
- Sex: women generally have a BMR about 10% lower (less muscle on average)
- Genetics: a variation of ±10-15% between individuals
- Hormones: an active thyroid raises BMR; chronic cortisol lowers it
A fresh angle: BMR cannot be drastically boosted by supplements or marketing tricks. The only real lever is increasing muscle mass (which takes strength training and enough protein).
A myth: “I have a slow metabolism”. Often the person is simply eating more than they think and moving little. Real BMR varies very little between individuals.
An important point: prolonged calorie restriction lowers BMR by about 10-20% (adaptation). This is why severe diets eventually stall: the body adapts.
A nuance: adaptive thermogenesis (the drop in BMR) is real but exaggerated by some. It does not put a ceiling on weight loss if the calorie deficit continues.