Resting Energy Expenditure

Definition

The amount of energy (measured in kilocalories) expended at rest to maintain basic physiological functions, calculated using predictive equations or measured by indirect calorimetry. Essential for determining caloric requirements.

How it works

Resting energy expenditure (REE) represents the calories needed for basic metabolic functions (breathing, circulation, protein synthesis, temperature regulation) without activity. REE can be measured precisely using indirect calorimetry, which analyzes oxygen consumption and CO2 production, or estimated using equations such as Harris-Benedict, Roza-Shizgal, or Mifflin-St Jeor. Multiplying REE by activity and stress factors gives total daily energy expenditure, guiding nutritional prescription. Understanding REE is critical because overfeeding causes metabolic complications while underfeeding causes malnutrition, so accurate calculation ensures appropriate caloric support.

Role

Provides the foundation for calculating total caloric requirements, guiding appropriate nutritional support intensity and preventing both overfeeding and underfeeding.

Examples

• REE 1800 kcal in 70 kg adult male
• REE ×1.2 activity factor = 2160 kcal in ambulatory patient
• REE ×1.5 stress factor = 2700 kcal in septic ICU patient

Recommendations

Use indirect calorimetry if available (gold standard), especially in critical illness. Use Mifflin-St Jeor equation for estimation (more accurate than Harris-Benedict). Multiply REE by appropriate activity factor (1.1-1.3 for bed rest, 1.3-1.5 for hospital/critical care). Reassess periodically and adjust based on weight trends.

Key takeaway

Accurate REE assessment prevents both overfeeding and underfeeding, optimizing nutritional support intensity and metabolic outcomes.

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