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Basal Metabolic Rate (BMR) is the number of calories your body requires to carry out basic life-sustaining functions while at complete rest. These functions include breathing, blood circulation, cell production, nutrient processing, and maintaining body temperature. Your BMR typically accounts for 60-75% of your total daily calorie expenditure.

Knowing your BMR is the foundation for understanding your overall energy needs. Whether you're planning a weight loss diet, building muscle, or simply trying to maintain a healthy weight, your BMR provides the baseline from which all calorie targets are calculated.

Mifflin-St Jeor vs. Harris-Benedict

The Mifflin-St Jeor equation is widely considered the most accurate for estimating BMR in healthy adults. It was developed in 1990 using contemporary population data and is recommended by the Academy of Nutrition and Dietetics. The Harris-Benedict equation, originally published in 1919 and revised in 1984, remains commonly used but may overestimate BMR by approximately 5% in certain populations.

Factors That Affect BMR

• Muscle mass: Lean muscle tissue burns more calories at rest than fat tissue. People with higher muscle mass have a higher BMR.
• Age: BMR decreases by about 1-2% per decade after age 20, largely due to loss of lean muscle mass.
• Thyroid function: The thyroid gland regulates metabolism. Hypothyroidism can lower BMR, while hyperthyroidism can increase it.
• Body size: Larger bodies require more energy for basic functions, resulting in a higher BMR.
• Gender: Males generally have a higher BMR than females due to greater average muscle mass and lower body fat percentage.
• Genetics: Inherited metabolic traits can cause BMR to vary between individuals of similar size and composition.
• Extreme dieting: Prolonged severe calorie restriction can lower BMR as the body adapts to conserve energy (metabolic adaptation).