Understanding Basal Metabolic Rate
BMR represents the minimum calories your body needs to sustain life while at complete rest — as if you were lying in bed all day. It powers breathing, heartbeat, brain function, cell repair, and temperature regulation. For most people, BMR accounts for 60–75% of total daily energy expenditure. Knowing your BMR is the foundation of any evidence-based nutrition plan.
The Mifflin-St Jeor Equation Explained
The Mifflin-St Jeor equation, published in 1990, is considered the most accurate predictive BMR formula by the American Dietetic Association. For males: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(years) + 5. For females: the same formula but −161 instead of +5. This accounts for the metabolic differences between sexes.
From BMR to TDEE
Total Daily Energy Expenditure (TDEE) adds your physical activity calories to your BMR. The Harris-Benedict activity factors range from 1.2 (sedentary) to 1.9 (very active). Your TDEE is the actual number of calories you burn in a day. To lose weight, eat below TDEE. To gain weight, eat above it. To maintain, match it as closely as possible.
Factors That Affect Your BMR
Several factors influence your BMR beyond weight, height, age, and sex. Muscle mass is the biggest variable — muscle burns more calories at rest than fat. Genetics play a role too, with some people naturally having faster metabolisms. Hormones (especially thyroid), body temperature, caffeine intake, and even climate can all shift your BMR up or down.
