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Harris-Benedict (BMR/TEE)

Basal metabolic rate and total energy expenditure estimation

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Why use it

Foundation for nutritional planning. Guides caloric prescriptions for weight maintenance, loss, or gain. Essential for calculating ICU/TPN nutritional targets. Simple bedside estimation without calorimetry.

About

The Harris-Benedict equation estimates Basal Metabolic Rate (BMR) based on sex, weight, height, and age. Multiplied by an activity factor, it provides Total Energy Expenditure (TEE). The revised (Roza-Shizgal 1984) version is more commonly used. This calculator provides both the original and revised equations, plus the Mifflin-St Jeor equation for comparison.

When to use

  • Nutritional assessment and caloric target setting
  • TPN/enteral nutrition prescription
  • Weight management counseling
  • ICU nutritional planning (with stress/activity factors)

Formula

Revised Harris-Benedict (Roza-Shizgal 1984): Male BMR = 88.362 + (13.397 × wt kg) + (4.799 × ht cm) - (5.677 × age) Female BMR = 447.593 + (9.247 × wt kg) + (3.098 × ht cm) - (4.330 × age) Mifflin-St Jeor: Male = (10 × wt) + (6.25 × ht) - (5 × age) + 5 Female = (10 × wt) + (6.25 × ht) - (5 × age) - 161 TEE = BMR × Activity Factor

Pearls & pitfalls

  • Harris-Benedict tends to overestimate by ~5% in obese patients.
  • Mifflin-St Jeor is considered more accurate for overweight/obese individuals.
  • In critically ill patients, indirect calorimetry is the gold standard when available.
  • ICU stress factors: 1.2 (mild stress), 1.3-1.5 (moderate-severe), up to 2.0 (burns > 40% TBSA).
  • Use adjusted body weight for obese patients: ABW = IBW + 0.25 × (Actual - IBW).
  • Protein needs are separate: 0.8 g/kg/day (normal), 1.2-2.0 g/kg/day (critical illness).

Next steps

Multiply BMR by activity factor for TEE. ICU patients: use stress factor 1.2-1.5 depending on condition. For weight loss: create 500-1000 kcal/day deficit. For TPN: calculate protein, carbohydrate, and lipid targets based on TEE.

Evidence

Original Harris-Benedict (1919) derived from healthy volunteers. Revised by Roza and Shizgal (1984). Mifflin-St Jeor (1990) shown to be most accurate in a 2005 ADA evidence analysis. All equations have ±10-15% error vs. indirect calorimetry.

References

  1. Harris JA, Benedict FG. A biometric study of human basal metabolism. Proc Natl Acad Sci USA. 1918;4(12):370-373. — link
  2. Mifflin MD et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247. — link