How to Determine REE: A Comprehensive Guide to Measuring Resting Energy Expenditure

November 19, 2025 •

3 min read

Resting energy expenditure (REE) accounts for 60-75% of a person's daily energy expenditure. Knowing how to determine REE accurately is crucial for effective weight management, clinical nutrition, and understanding your metabolism.

Quick Summary

Resting energy expenditure (REE) can be measured using indirect calorimetry or estimated with predictive equations. This guide explains the methodologies, comparing their accuracy and outlining the factors that influence your metabolic rate.

Key Points

Indirect Calorimetry: The gold standard for measuring REE involves analyzing your breath to measure oxygen consumption and carbon dioxide production.
Predictive Equations: Formulas like Mifflin-St Jeor and Harris-Benedict can estimate REE but are less accurate, especially in clinical settings and for individuals with obesity.
Lean Body Mass (FFM) is Key: Your muscle and organ mass is the strongest determinant of your REE, making it more metabolically active than fat mass.
REE Decreases with Age: Your metabolic rate naturally declines as you get older, largely due to a decrease in lean body mass.
Accurate REE is Critical for Weight Loss: Precise REE measurement helps prevent metabolic adaptation from excessive calorie restriction, which can hinder weight loss efforts.
Personalized Nutrition: Using your REE data, a registered dietitian can create a tailored diet plan that prevents overfeeding or underfeeding and improves dietary outcomes.

What is Resting Energy Expenditure (REE)?

Resting Energy Expenditure (REE) represents the calories your body burns at rest for basic functions like breathing and circulation. It is the largest part of your daily energy use and is vital for personalized nutrition. While often confused with Basal Metabolic Rate (BMR), REE is measured under less strict conditions. Understanding how to determine REE helps create precise strategies for weight management and clinical care.

Methods to Determine REE

Determining REE can be done through direct measurement or estimation using equations.

Indirect Calorimetry: The Gold Standard

Indirect calorimetry (IC) is the most accurate method. It measures oxygen consumption and carbon dioxide production from breath analysis, using these values to calculate energy expenditure.

The Indirect Calorimetry Procedure

For accurate results:

Fasting: Fast for 8-12 hours.
Rest: Rest comfortably in a quiet environment.
Measurement: A canopy or mask is used to analyze gas exchange.
Interpretation: IC also provides the respiratory quotient (RQ), indicating fuel source.

Predictive Equations: Convenient Estimation

Predictive equations use age, sex, height, and weight to estimate REE when IC is not feasible.

Common Predictive Equations

Mifflin-St Jeor Equation: Often reliable for adults, including those with obesity.
- For men: $(10 imes \text{weight in kg}) + (6.25 imes \text{height in cm}) - (5 imes \text{age in years}) + 5$
- For women: $(10 imes \text{weight in kg}) + (6.25 imes \text{height in cm}) - (5 imes \text{age in years}) - 161$
Harris-Benedict Equation: Developed in 1919, may overestimate REE in current populations.
- For men: $66.5 + (13.8 imes \text{weight in kg}) + (5.0 imes \text{height in cm}) - (6.8 imes \text{age in years})$
- For women: $655.1 + (9.6 imes \text{weight in kg}) + (1.8 imes \text{height in cm}) - (4.7 imes \text{age in years})$

The Accuracy of Predictive Equations

Predictive equations are less precise and their accuracy varies based on factors like ethnicity, age, and BMI. They can lead to significant errors in clinical settings and for individuals with extreme body weights.

Factors Influencing REE

Several factors cause individual variations in REE:

Body Composition: Lean body mass (muscle and organs) is more metabolically active than fat mass and is the primary determinant of REE.
Age: REE decreases with age, mainly due to reduced lean body mass.
Sex: Men typically have higher REE due to more lean body mass.
Genetics: Genetic makeup can influence metabolic rate.
Diet: Severe calorie restriction can lower REE through metabolic adaptation.
Hormones: Hormones like thyroid hormones impact metabolic rate.
Health Conditions: Illnesses, fever, and certain medical conditions can alter REE.

Method Comparison: Indirect Calorimetry vs. Predictive Equations


Feature	Indirect Calorimetry	Predictive Equations
Accuracy	High. Gold standard for precise measurement.	Low to moderate. Significant error potential, especially in clinical and obese populations.
Cost	High. Requires expensive equipment and trained personnel.	Very low. Only requires a simple calculation.
Accessibility	Limited. Mostly available in clinical or research settings.	High. Can be used by anyone with standard anthropometric data (age, sex, height, weight).
Clinical Use	Recommended for critically ill patients, obese individuals, and other cases where precise nutritional support is critical.	Often used when IC is unavailable, though accuracy is a significant concern. Can be a starting point for healthy adults.
Best For	Accurate diagnosis, guiding nutritional support in medically complex cases, and personalized weight management strategies.	General screening and for individuals without major metabolic abnormalities, but with caution.

Conclusion

Understanding how to determine REE is crucial for personalized health and nutrition. Indirect calorimetry offers the most accurate data but may not always be practical. Predictive equations provide a convenient, low-cost estimate but are less precise and should be used cautiously, especially for those with metabolic conditions or significant weight concerns. For complex cases, IC provides the precise data needed for effective, evidence-based nutritional plans. For further information on the Nutrition Care Process, refer to eatrightpro.org.

Frequently Asked Questions

The most accurate method is indirect calorimetry, which directly measures your oxygen consumption and carbon dioxide production to calculate your metabolic rate.

Online calculators typically use predictive equations like Mifflin-St Jeor or Harris-Benedict. While convenient, these are estimates and may not be accurate for every individual, especially those with unique metabolic needs or body compositions.

Knowing your REE allows you to set a precise and appropriate calorie target. This helps prevent metabolic adaptation, where your body slows its metabolism in response to severe calorie restriction, which can stall weight loss.

Indirect calorimetry measures the amount of oxygen your body consumes and the carbon dioxide it produces. Since energy is released by burning fuel (macronutrients), the amount of gas exchanged is directly proportional to the amount of energy you are expending.

Yes, REE naturally declines with age. This is largely due to age-related changes in body composition, such as a decrease in lean body mass.

Yes, for the most accurate results, you must fast for at least 8-12 hours before the test. This ensures the measurement reflects your resting state and not the energy expended digesting food.

REE (Resting Energy Expenditure) is measured under less strict conditions (e.g., after an overnight fast and rest). BMR (Basal Metabolic Rate) is measured under more stringent conditions, specifically after a full night's sleep in a thermoneutral environment.