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About

The Harris-Benedict equation estimates basal metabolic rate based on gender, weight, height, and age. This tool utilizes the 1984 Roza and Shizgal revision. Medical professionals often prefer this version for specific clinical comparisons alongside the Mifflin-St Jeor equation. Accuracy relies on precise input of physical characteristics. Errors in height or weight measurements propagate through the linear coefficients. The formula assumes a resting state in a thermoneutral environment. It does not account for lean body mass directly. Individuals with high muscle mass may find this underestimates needs. Conversely, it may overestimate needs for individuals with higher body fat percentages.

bmr tdee calories metabolism roza-shizgal

Formulas

The 1984 Roza and Shizgal revision defines BMR as:

{
Pmen = 88.362 + (13.397 × m) + (4.799 × h) (5.677 × a)Pwomen = 447.593 + (9.247 × m) + (3.098 × h) (4.330 × a)

Where P is heat production (kcal/day), m is mass (kg), h is height (cm), and a is age (years). TDEE is calculated by multiplying P by the activity factor f.

Reference Data

Activity LevelMultiplierDescriptionExample (BMR 1600)
Sedentary1.2Little or no exercise, desk job1920 kcal
Lightly Active1.375Light exercise/sports 1-3 days/week2200 kcal
Moderately Active1.55Moderate exercise/sports 3-5 days/week2480 kcal
Very Active1.725Hard exercise/sports 6-7 days/week2760 kcal
Extra Active1.9Very hard exercise/physical job3040 kcal
Physical Job (Low)1.4Standing work, light lifting2240 kcal
Physical Job (High)2.0Construction, farming, heavy lifting3200 kcal
Athlete (Endurance)2.2Competitive training (2+ hours/day)3520 kcal

Frequently Asked Questions

The original 1919 data relied on a population with different lifestyle and nutritional standards than today. The 1984 Roza and Shizgal revision recalibrated the constants to better align with modern metabolic data, improving accuracy for contemporary populations.
Harris-Benedict (1984) tends to predict slightly higher caloric needs than Mifflin-St Jeor. Dietitians often calculate both to establish a caloric range (minimum to maximum) for a patient, rather than relying on a single data point.
Standard metabolic formulas become less linear at extremes of body weight. For individuals with obesity, the equation may overestimate metabolic rate because fat tissue is less metabolically active than muscle tissue. Adjustment using "Adjusted Body Weight" is sometimes applied in clinical settings.