Understanding Basal Metabolic Rate (BMR) and Resting Metabolic Rate (RMR)
It's helpful to understand the difference between BMR and RMR, though they are often used interchangeably.
- Basal Metabolic Rate (BMR): This is the minimal calories required for essential bodily functions at complete rest under strict clinical conditions, including fasting and a neutral environment.
- Resting Metabolic Rate (RMR): RMR, or Resting Energy Expenditure, is the calories burned at rest under less strict conditions, like after an overnight fast. It's typically about 10% higher than BMR and is a more practical measure for most people.
Accurate methods for measuring metabolic rate
For the most precise measurement, clinical testing is recommended.
Lab-based testing: Indirect calorimetry
Indirect calorimetry is the most accurate clinical method, determining energy expenditure by measuring oxygen consumption and carbon dioxide production.
The Process: You breathe into a mask for 15-20 minutes while relaxed, and a device analyzes gas exchange to calculate your RMR. These tests are available at various health and fitness facilities.
At-home estimation: Predictive equations
Conveniently, you can estimate your metabolic rate using equations like the Mifflin-St Jeor and revised Harris-Benedict formulas.
Mifflin-St Jeor Equation
This formula is widely used for its accuracy in modern lifestyles:
- For Men: BMR = (10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) + 5
- For Women: BMR = (10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) – 161
Harris-Benedict Equation
An older, revised formula:
- For Men: BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) – (5.677 x age in years)
- For Women: BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) – (4.330 x age in years)
Other accessible methods
- Bioelectrical Impedance Analysis (BIA): Some scales estimate metabolic rate based on body composition, though accuracy varies with hydration.
- Fitness Trackers and Wearables: Devices like smartwatches estimate total daily calorie burn (TDEE), not just RMR, with varying accuracy.
Factors that influence your metabolic rate
Your metabolic rate is influenced by several factors:
Comparison of Metabolic Rate Influencers
| Factor | How It Influences Metabolic Rate | Can You Change It? |
|---|---|---|
| Body Composition | More muscle means a higher BMR as it burns more calories than fat at rest. | Yes, through strength training and diet. |
| Age | BMR declines with age, mainly due to muscle loss, especially after 30. | You can slow the decline with activity and muscle building. |
| Gender | Men generally have a higher BMR due to more muscle and less fat. | No, this is biological, but lifestyle choices can still boost metabolism. |
| Genetics | Genes influence natural metabolism efficiency. | No, this is unchangeable. |
| Thyroid Hormones | Regulate metabolism; conditions like hypothyroidism can slow it. | Yes, with medical treatment. |
| Environmental Temperature | Body burns more calories to maintain temperature in extreme heat or cold. | Limited impact on long-term metabolic change. |
Using your metabolic rate for weight management
Knowing your metabolic rate helps determine your Total Daily Energy Expenditure (TDEE) and manage weight.
- Calculate RMR/BMR: Use an online calculator with a formula or get a clinical test.
- Determine Activity Level: Multiply your RMR by an activity factor (1.2 for sedentary to 1.9 for extremely active).
- Find Your TDEE: The result is your daily calorie burn.
- Manage Calories: Consume fewer calories than your TDEE for weight loss, match it for maintenance, or consume more to gain.
How to increase your metabolic rate
Lifestyle changes can positively affect your metabolism:
- Build Muscle: Strength training increases metabolically active muscle mass, boosting resting calorie burn.
- HIIT: High-Intensity Interval Training increases metabolism for hours post-workout due to EPOC.
- Eat Protein: Protein has a higher thermic effect, burning more calories during digestion and preserving muscle.
- Stay Hydrated: Drinking water can temporarily boost metabolism and is vital for metabolic functions.
- Get Enough Sleep: Sleep deprivation negatively impacts hormones regulating appetite and energy.
- Avoid Crash Diets: Severe calorie restriction can slow metabolism as the body conserves energy.
Conclusion
To know your metabolic rate accurately, consider clinical indirect calorimetry or use reliable at-home equations. Understanding your BMR/RMR and influencing factors like body composition and activity level is crucial for effective weight management. Use this knowledge to inform your nutrition and exercise choices. Consulting a healthcare provider or dietitian can offer a personalized approach. The goal is to build a sustainable, healthy lifestyle that supports your body's energy needs. For more on predictive formulas, visit the National Academy of Sports Medicine website.
