Mifflin-St Jeor Equation (Male)
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Variables
| Symbol | Name | Unit | Description |
|---|---|---|---|
| $BMR$ | Basal Metabolic Rate | kcal/day | Calories burned at complete rest over 24 hours. |
| $w$ | Body weight | kg | Total body mass in kilograms. |
| $h$ | Height | cm | Standing height in centimetres. |
| $a$ | Age | years | Age in whole years. |
What Is the Mifflin-St Jeor Equation?
The Mifflin-St Jeor equation estimates Basal Metabolic Rate (BMR) — the number of calories the body burns while completely at rest over a 24-hour period. For males, the equation is:
$$BMR = 10w + 6.25h - 5a + 5$$
Where w is weight in kg, h is height in cm, and a is age in years.
Why BMR Matters
BMR represents the minimum energy required to maintain vital functions: breathing, circulation, cell repair, temperature regulation, and organ function. It typically accounts for 60–75% of total daily energy expenditure (TDEE). Knowing your BMR is the foundation for any evidence-based nutrition plan, whether the goal is weight loss, maintenance, or muscle gain.
How the Coefficients Work
- 10 × weight: Heavier bodies require more energy to sustain cellular activity; each kg contributes ~10 kcal/day at rest.
- 6.25 × height: Taller people have larger organ surface area and more lean tissue; each centimetre adds ~6.25 kcal/day.
- −5 × age: Metabolic rate declines with age (roughly 1–2% per decade after 20) as lean muscle mass decreases.
- +5 (male constant): Men have on average more lean mass and less body fat than women at the same weight and height, resulting in a higher BMR.
Comparison with Other Equations
| Equation | Developed | MAE vs Measured |
|---|---|---|
| Mifflin-St Jeor | 1990 | ~10% |
| Harris-Benedict (revised) | 1984 | ~12% |
| Katch-McArdle | 1975 | ~8% (needs body fat %) |
A 2005 Academy of Nutrition and Dietetics review found Mifflin-St Jeor to be the most accurate predictive equation for the general non-athletic population when body-fat percentage is unknown.
Common Misconceptions
- BMR = calories you should eat — No. BMR is a floor. You must multiply by an activity factor to get TDEE before designing a diet.
- BMR is constant — It changes with weight, age, hormonal status, and adaptation to prolonged caloric restriction.
- The same equation applies to women — No. Women use a −161 constant instead of +5 (see Mifflin-St Jeor Female formula).
Derivation & History
Mark D. Mifflin and Sachiko T. St Jeor published this equation in 1990 in the American Journal of Clinical Nutrition after measuring resting metabolic rate (RMR) in 498 volunteers (both obese and non-obese) using indirect calorimetry — a gold-standard method that measures oxygen consumption and carbon dioxide production to calculate energy expenditure.
The research team used multiple regression analysis to find the combination of weight, height, and age that best predicted measured RMR. They produced sex- specific equations because lean body mass differs systematically between males and females. The resulting equation proved more accurate than the 1919 Harris-Benedict equation and became the clinical standard recommended by major dietetic associations worldwide.
Worked Examples
30-year-old male, moderately active
- 10 × 80 = 800
- 6.25 × 175 = 1,093.75
- 5 × 30 = 150
- BMR = 800 + 1,093.75 − 150 + 5 = 1,748.75 kcal/day
Result: BMR ≈ 1,749 kcal/day
45-year-old male, sedentary
- 10 × 95 = 950
- 6.25 × 180 = 1,125
- 5 × 45 = 225
- BMR = 950 + 1,125 − 225 + 5 = 1,855 kcal/day
Result: BMR ≈ 1,855 kcal/day
Edge Cases & Limitations
Children and adolescents: The equation was validated on adults; paediatric BMR uses age-specific equations (e.g., Schofield).
Extreme obesity (BMI > 40): The equation tends to underestimate BMR in severely obese individuals because fat tissue contributes relatively little to metabolic rate; lean body-mass equations (Katch-McArdle) may be more accurate.
Athletes: Highly trained athletes have more lean mass per kilogram of body weight, so the equation may underestimate their BMR.
Illness or injury: Fever, trauma, surgery, and hyperthyroidism all substantially elevate BMR beyond what the equation predicts.
Real-World Applications
Registered dietitians use BMR (combined with an activity multiplier) to calculate personalised calorie targets for weight management patients. Sports nutritionists apply it to periodise an athlete's energy intake across training and competition phases. Bariatric surgery programmes use pre-operative BMR to predict post-operative calorie needs. Fitness apps (MyFitnessPal, Cronometer) rely on Mifflin-St Jeor as their default BMR algorithm for generating daily calorie goals.