What is Resting Energy Expenditure (REE)?
Resting energy expenditure (REE) is the number of calories your body burns at rest to maintain vital functions like breathing, circulating blood, and regulating temperature. The terms REE and Basal Metabolic Rate (BMR) are often used interchangeably, although BMR is technically measured under more restrictive, fasted conditions. For practical purposes, REE provides an excellent estimate of your foundational calorie needs. It is the largest component of your total daily energy expenditure (TDEE), typically accounting for 60% to 75% of the total calories you burn each day.
The Difference Between REE and TDEE
REE is the energy required to keep your body functioning at rest, while TDEE is the total number of calories you burn throughout the day, including all physical activity. TDEE is calculated by multiplying your REE by an activity factor based on your daily movement.
How to Calculate Resting Energy for a Woman
While indirect calorimetry provides the most accurate lab-based measurement of RMR, several widely accepted equations can be used to get a reliable estimate at home. The Mifflin-St Jeor equation is generally considered the most accurate predictor for women today.
Using the Mifflin-St Jeor Equation
The Mifflin-St Jeor formula for women is: $$RMR = (10 \times \text{weight in kg}) + (6.25 \times \text{height in cm}) - (5 \times \text{age in years}) - 161$$
Example: For a 35-year-old woman who is 170 cm (5'7") tall and weighs 68 kg (150 lbs): $$RMR = (10 \times 68) + (6.25 \times 170) - (5 \times 35) - 161$$ $$RMR = 680 + 1062.5 - 175 - 161 = 1406.5 \text{ calories}$$
Mifflin-St Jeor vs. Harris-Benedict Formulas
| Feature | Mifflin-St Jeor Formula | Harris-Benedict Formula |
|---|---|---|
| Development Year | 1990s | 1918 (revised 1984) |
| Considered Accuracy | Generally more accurate | Older, can overestimate calorie needs |
| Equation (Women) | RMR = (10 kg) + (6.25 cm) - (5 * age) - 161 | RMR = 447.593 + (9.247 kg) + (3.098 cm) - (4.330 * age) |
| Best for | Most populations | Historical context, still widely used but less precise |
Factors Affecting a Woman's Resting Energy
Several biological and lifestyle factors influence your resting energy expenditure:
- Body Composition: The ratio of muscle to fat significantly affects your REE. Muscle tissue is more metabolically active than fat tissue, meaning it burns more calories at rest. This is a primary reason why men typically have higher metabolic rates than women.
- Age: As you age, your metabolic rate naturally slows down. This is mainly due to a decrease in lean body mass and hormonal shifts.
- Genetics: Your genetic makeup plays a role in determining your metabolic rate, accounting for some of the variance seen among individuals.
- Hormonal Health: Thyroid hormones are key regulators of metabolism. Conditions like hypothyroidism can slow down your RMR, while hyperthyroidism can speed it up.
- Sleep Quality: Chronic sleep deprivation can negatively impact your metabolism by disrupting hormones like ghrelin (hunger) and leptin (satiety), which can lead to weight gain.
- Dietary Intake: Drastic calorie restriction can cause a significant drop in your RMR as your body tries to conserve energy, a phenomenon known as metabolic adaptation. Consuming enough protein can help preserve lean muscle mass during weight loss.
Strategies for Increasing Your Resting Energy
While you can't change your age or genetics, several lifestyle changes can help boost your resting energy over time.
Build and Maintain Muscle Mass
Resistance or strength training is one of the most effective ways to increase your REE. As muscle is more metabolically active than fat, building lean muscle tissue means your body burns more calories even when you are not exercising. Incorporate activities like lifting weights, using resistance bands, or bodyweight exercises into your routine.
Eat Enough Protein
Protein has a higher thermic effect of food (TEF) than carbohydrates or fats. TEF is the energy your body uses to digest, absorb, and process nutrients. Aiming for adequate protein intake can slightly increase your overall calorie burn and help preserve muscle mass, which prevents the metabolic slowdown often associated with dieting.
Stay Hydrated
Research has shown that drinking enough water helps all of your body's metabolic processes function properly. Mild dehydration can cause your metabolism to slow down. One study found that drinking half a liter of water can temporarily boost metabolism by up to 30% for over an hour.
Prioritize Quality Sleep
Getting 7 to 9 hours of quality sleep per night is crucial for metabolic health. Poor sleep can disrupt hormone levels and insulin sensitivity, which negatively impacts your metabolic rate. Creating a consistent sleep schedule can help regulate these processes and support a healthy metabolism.
Don't Drastically Restrict Calories
Extreme calorie-restricted diets can trigger a metabolic slowdown as your body enters a starvation mode to conserve energy. Focus instead on a modest, sustainable calorie deficit combined with nutrient-dense foods and regular exercise to support a healthy metabolism and weight loss.
Conclusion: Personalizing Your Energy Needs
Understanding what should my resting energy be for a woman is a foundational piece of any health and wellness strategy. While calculators provide useful estimates, your unique metabolic rate is influenced by a complex mix of genetics, lifestyle, and body composition. By incorporating strength training, prioritizing protein, staying hydrated, and getting enough sleep, you can support a healthy metabolism and work toward your weight management goals. Remember that consulting a healthcare provider or a registered dietitian is always the best way to get a tailored plan for your specific needs.
For more in-depth information on metabolic rate, refer to reliable health resources like the Cleveland Clinic's breakdown on metabolism: Metabolism: What It Is, How It Works & Disorders.
