What is Resting Energy (RMR)?
Resting energy, more formally known as Resting Metabolic Rate (RMR) or Resting Energy Expenditure (REE), is the total number of calories your body burns while at complete rest, but awake. This energy powers all of your body's fundamental, involuntary functions, such as breathing, blood circulation, cell production, nutrient processing, and maintaining body temperature. It is the largest component of your Total Daily Energy Expenditure (TDEE), often accounting for 60-75% of the total calories you burn each day.
While the terms RMR and Basal Metabolic Rate (BMR) are often used interchangeably, there is a slight technical difference. BMR is a more restrictive measurement, representing the absolute minimum number of calories needed to sustain life in a completely fasted, non-stressed, and thermoneutral state, and is typically only measured in a clinical lab. RMR, a more practical measurement for most people, reflects the calories burned during a state of rest but not under the strict conditions of a BMR test, and is about 10-20% higher than BMR. For most practical purposes, the RMR is the metric that helps determine a person's daily energy needs.
Key Factors That Influence Your Resting Energy
Your resting energy is not a static number and is influenced by a number of variables. Understanding these factors can help explain why calorie needs differ so much between individuals:
- Body Composition: This is one of the most significant factors. Lean body mass (muscle) is far more metabolically active than fat tissue, meaning it burns more calories at rest. An individual with more muscle mass will have a higher RMR than someone of the same weight with a higher body fat percentage.
- Gender: On average, men tend to have a higher RMR than women. This is largely due to men having a greater amount of lean body mass and typically being larger in stature.
- Age: RMR naturally decreases with age. After about age 20, RMR can decrease by roughly 2-3% per decade due to a combination of factors, including the natural loss of muscle mass.
- Weight and Height: Larger and taller individuals have a higher RMR because they have more body mass and more metabolizing tissue to maintain.
- Genetics: Individual genetic makeup plays a role in determining metabolic rate, which is why some people are born with naturally faster or slower metabolisms.
- Hormonal Status: Hormones, such as those from the thyroid gland, can significantly impact RMR. Conditions like hyperthyroidism can increase RMR, while hypothyroidism can decrease it.
- Environmental Temperature: Being in an extremely cold or hot environment can temporarily increase RMR as your body expends energy to maintain its core temperature.
How to Estimate Your Resting Energy
While the most accurate way to measure your RMR is through indirect calorimetry in a clinical setting, several equations provide a reliable estimate. The Mifflin-St Jeor equation is often considered one of the most accurate for estimating RMR.
Mifflin-St Jeor Equation:
- For Men: RMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) + 5
- For Women: RMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) - 161
Example Calculation: A 35-year-old woman who is 165 cm tall and weighs 68 kg would have an estimated RMR of:
- RMR = (10 × 68) + (6.25 × 165) - (5 × 35) - 161
- RMR = 680 + 1031.25 - 175 - 161 = 1375.25 kcal/day
This means her body burns approximately 1,375 calories per day just to function at rest.
Using Your Resting Energy for Weight Management
Your RMR is the starting point for calculating your total daily calorie needs, or TDEE. To find your TDEE, you multiply your RMR by an activity factor. This is a vital step for anyone aiming to lose, maintain, or gain weight.
Comparison of Activity Levels and Multipliers
| Activity Level | Description | Activity Factor | Example TDEE Calculation |
|---|---|---|---|
| Sedentary | Little to no exercise | 1.2 | $1375 \times 1.2 = 1650$ calories |
| Lightly Active | Light exercise/sports 1-3 days/week | 1.375 | $1375 \times 1.375 = 1891$ calories |
| Moderately Active | Moderate exercise/sports 3-5 days/week | 1.55 | $1375 \times 1.55 = 2131$ calories |
| Very Active | Hard exercise/sports 6-7 days/week | 1.725 | $1375 \times 1.725 = 2372$ calories |
| Extra Active | Very hard exercise/physical job/training | 1.9 | $1375 \times 1.9 = 2613$ calories |
Note: Calculations use the example RMR of 1375 kcal.
How to Influence Your Resting Energy
While genetics and age are fixed factors, you can influence your RMR and overall metabolic rate through lifestyle choices. Building lean muscle mass is the most impactful way to sustainably increase your resting energy expenditure. Muscle tissue is more metabolically active than fat, so increasing your muscle mass means your body will burn more calories at rest. Strength training is key for building and maintaining this metabolically active tissue.
Additionally, high-intensity interval training (HIIT) can provide a temporary boost to your RMR, a phenomenon known as excess post-exercise oxygen consumption (EPOC) or "afterburn". Other healthy habits like getting enough sleep, staying hydrated, and eating adequate protein can also support a healthy metabolism. Conversely, extreme calorie restriction or prolonged dieting can cause your metabolism to slow down as your body conserves energy, a phenomenon known as adaptive thermogenesis.
Conclusion: Finding your personal baseline
So, what is a good resting energy? There is no single universal number. Instead, a "good" resting energy is one that is appropriate for your unique body, considering factors like age, gender, weight, height, and body composition. By understanding your RMR and how it is influenced, you gain a powerful tool for managing your health. Calculating your RMR provides a personalized baseline for determining your total daily calorie needs, allowing you to set more effective and sustainable health and fitness goals. Remember, focus on supporting your metabolism through a balanced diet, consistent exercise (especially strength training), and a healthy lifestyle to ensure your body functions at its best.
A note on accuracy
While predictive equations like Mifflin-St Jeor provide a useful estimate, they are not perfect. Factors like underlying health conditions or significant differences in body composition can affect accuracy. If you have specific health concerns or are training for a competitive sport, consulting with a healthcare professional or registered dietitian for a clinical measurement and personalized plan is recommended.
Key Outbound Link
For further reading on the science behind Resting Energy Expenditure, consider exploring resources from reputable institutions like the National Institutes of Health (NIH): https://www.ncbi.nlm.nih.gov/books/NBK591031/
