Basal Metabolic Rate (BMR)
Energy expended at rest to maintain vital functions
Definition
Basal Metabolic Rate (BMR) is the amount of energy (kilocalories) the body requires at complete rest in a neutral environment to sustain vital functions: heart contraction, respiration, temperature regulation, and cellular metabolism.
Factors Affecting BMR
- Age: decreases with age
- Sex: higher in males (more muscle mass)
- Body composition: lean mass increases, fat decreases
- Thyroid hormone: hyperthyroidism elevates, hypothyroidism lowers
- Fever: each 1°F increase raises BMR ~7%
- Pregnancy, lactation, growth: increased
Clinical Applications
Nutritional planning uses BMR to estimate total energy expenditure (TEE = BMR × activity factor × stress factor). In critically ill patients, indirect calorimetry provides more accurate measurements.
Nursing Considerations
Recognize clinical cues: hyperthyroid patients lose weight despite increased intake and have heat intolerance; hypothyroid patients gain weight, feel cold, and have constipation. Adjust caloric recommendations accordingly.
NCLEX Relevance
Tested in nutrition and thyroid disorder content. Expect questions linking metabolic rate to weight changes and temperature preference.