Is BMR Useful?
Basal Metabolic Rate, what it is, the equations, and where it falls short.
BMR stands for Basal Metabolic Rate. It's the number of calories your body needs during complete rest over 24 hours. This energy maintains essential functions: cell reproduction in vital organs like the heart, lungs, kidneys, nervous system, intestines, liver, sex organs, muscles and skin. Processing nutrients, circulation and breathing all cost energy, counted as calories per day.
BMR calculations
Two primary equations are commonly used.
Harris & Benedict Equation
Men: BMR = 66.5 + (13.75 × weight kg) + (5.003 × height cm) − (6.775 × age)
Women: BMR = 655.1 + (9.563 × weight kg) + (1.850 × height cm) − (4.676 × age)
Mifflin-St Jeor Equation
Men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
Women: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
Practical value
Knowing your BMR helps you estimate your total daily calorie need when active: multiply the BMR value by 1.2 to 1.9 depending on your activity level. This is essential when you want to change your body composition, whether you're gaining muscle or losing body fat.
Key limitations
The equations have real weaknesses. Body composition isn't factored in, even though muscle mass increases BMR while body fat lowers it. And a long, low-calorie diet can reduce BMR by as much as 30%, an adjustment the formulas don't reflect.
Despite these shortcomings, BMR is still a useful planning tool, as long as you understand it with the right caution.