What is BMR and Why Is It Not Enough?
Your Basal Metabolic Rate (BMR) is the number of calories your body burns to perform basic, life-sustaining functions at complete rest, such as breathing, blood circulation, and cell production. It's the minimum amount of energy needed to keep your body functioning. While BMR is a critical starting point for calculating your daily calorie needs, it does not represent the full picture of your body's energy expenditure. A common mistake is using BMR as your daily calorie target, which would be inaccurate for anyone who doesn't spend their entire day at rest.
To move from BMR to a more practical number for planning your diet and exercise, you must add the calories burned from three other key areas. These components together form your Total Daily Energy Expenditure (TDEE).
The Three Components to Add to BMR
To find your true daily energy expenditure, you must incorporate three additional thermogenesis components that represent all the energy burned outside of your basal metabolic processes.
1. Thermic Effect of Food (TEF)
TEF is the energy your body uses to digest, absorb, and metabolize the food you eat. It requires energy to process the calories you consume. The TEF varies depending on the type of macronutrient:
- Protein: Has the highest thermic effect, requiring 20-30% of its calories to be burned during digestion.
- Carbohydrates: Have a moderate thermic effect, burning 5-10% of their calories.
- Fats: Have the lowest thermic effect, typically requiring 0-3% of their calories.
On average, TEF accounts for about 10% of your total daily energy expenditure. Choosing foods with a higher TEF, like lean protein, can slightly increase your overall metabolic rate.
2. Exercise Activity Thermogenesis (EAT)
EAT refers to the calories you burn during intentional, structured exercise. This includes activities such as:
- Running
- Weightlifting
- Cycling
- Swimming
- Organized sports
For many, EAT is a powerful and direct way to create a calorie deficit for weight loss. The amount of energy burned through EAT is highly dependent on the intensity and duration of your workout.
3. Non-Exercise Activity Thermogenesis (NEAT)
NEAT is the energy expended for all physical activities that are not formal exercise. This includes everything from standing and fidgeting to walking and cleaning. NEAT can vary significantly between individuals and can have a major impact on your total calorie expenditure. Boosting your NEAT throughout the day is an effective way to increase calorie burn, especially for those with sedentary jobs.
Here are some simple ways to increase your NEAT:
- Taking the stairs instead of the elevator
- Pacing while on the phone
- Doing household chores
- Fidgeting while sitting
- Taking a walk during your lunch break
Combining BMR with Activity Factors
Instead of calculating TEF, EAT, and NEAT separately, the most common method is to use an activity factor to multiply your BMR. This gives you a reliable estimate of your TDEE for weight management.
Comparison of Activity Levels for TDEE Calculation
| Activity Level | Description | BMR Multiplier | TDEE Calculation |
|---|---|---|---|
| Sedentary | Little to no exercise. | BMR x 1.2 | BMR * 1.2 |
| Lightly Active | Light exercise or sports 1-3 days per week. | BMR x 1.375 | BMR * 1.375 |
| Moderately Active | Moderate exercise or sports 3-5 days per week. | BMR x 1.55 | BMR * 1.55 |
| Very Active | Hard exercise or sports 6-7 days a week. | BMR x 1.725 | BMR * 1.725 |
| Extra Active | Very hard exercise, intense training, or a physical job. | BMR x 1.9 | BMR * 1.9 |
How to Use Your TDEE
Once you have your TDEE, you can use it to determine your daily calorie intake based on your goals:
- Maintain Weight: Consume calories equal to your TDEE.
- Lose Weight: Consume fewer calories than your TDEE, typically creating a deficit of 300-500 calories.
- Gain Weight: Consume more calories than your TDEE, usually adding 250-500 calories.
The Katch-McArdle Formula
For more athletic individuals, the Katch-McArdle formula can be more accurate as it accounts for lean body mass, which has a higher metabolic rate than fat mass. It is often used to calculate a more precise BMR for those with a known body fat percentage. The formula is:
$BMR = 370 + (21.6 imes ext{lean body mass in kg})$
After calculating your BMR using this method, you would then multiply it by the appropriate activity factor from the table above to find your TDEE.
Practical Steps to Apply This Knowledge
- Calculate Your BMR: Use a modern equation like the Mifflin-St Jeor formula, which is generally considered more accurate than the older Harris-Benedict formula.
- Men: $(10 imes ext{weight in kg}) + (6.25 imes ext{height in cm}) - (5 imes ext{age in years}) + 5$
- Women: $(10 imes ext{weight in kg}) + (6.25 imes ext{height in cm}) - (5 imes ext{age in years}) - 161$
- Determine Your Activity Level: Be honest with yourself and choose the multiplier that best fits your lifestyle from the table above. It's easy to overestimate your activity.
- Calculate Your TDEE: Multiply your BMR by your chosen activity factor to get your estimated total daily calorie burn.
- Set Your Calorie Goal: Based on whether you want to maintain, lose, or gain weight, adjust your intake relative to your TDEE.
Conclusion
In summary, to answer the question of what to add to BMR, the answer is the combined energy expenditure from the Thermic Effect of Food (TEF), Exercise Activity Thermogenesis (EAT), and Non-Exercise Activity Thermogenesis (NEAT). Combining these elements with your BMR allows you to accurately determine your Total Daily Energy Expenditure (TDEE). Instead of calculating each component separately, the most common and practical approach is to multiply your BMR by an appropriate activity factor. This provides a solid foundation for managing your calorie intake, achieving your weight goals, and maintaining a healthy lifestyle. Understanding the difference between BMR and TDEE is crucial for making informed decisions about your nutrition and fitness regimen.
For further reading, see:
Myprotein IE. How To Calculate BMR & TDEE (& Why It's Important). Myprotein.ie, 2023.
Can I use my BMR to set my daily calorie goals?
No, you should not use your BMR to set your daily calorie goals. Your BMR only represents the minimum calories your body needs at complete rest. For accurate calorie planning, you should use your Total Daily Energy Expenditure (TDEE), which accounts for your BMR plus all physical activity.
How does the Thermic Effect of Food (TEF) work?
TEF is the energy your body burns to digest, absorb, and process the nutrients from the food you eat. It accounts for a small but significant portion of your total energy expenditure. Protein has the highest thermic effect, meaning it requires more energy to digest compared to carbohydrates and fats.
What are some examples of Non-Exercise Activity Thermogenesis (NEAT)?
NEAT includes all the calories you burn from physical activity that isn't formal exercise. Examples include walking, cleaning, gardening, fidgeting, and standing. Increasing your NEAT is a simple way to boost your daily calorie expenditure.
How does muscle mass affect BMR?
Increased muscle mass directly influences your BMR. Lean muscle tissue burns more calories at rest than fat tissue. As a result, individuals with more muscle mass will have a higher BMR, even when sedentary.
Is there a different way to calculate BMR for very lean individuals?
Yes, very lean or athletic individuals may find the Katch-McArdle formula more accurate because it uses lean body mass instead of total body weight, which can lead to a better BMR estimate.
How can I be sure I am using the correct activity factor?
It is easy to overestimate your activity level. A good strategy is to use a step tracker and reflect honestly on your daily movement. If you have a desk job and do not work out consistently, you are likely in the 'Sedentary' or 'Lightly Active' category.
How often should I recalculate my TDEE?
You should recalculate your TDEE whenever there is a significant change in your weight or activity level. Recalculating after a weight change of 5-10% is generally recommended to ensure your calorie goals remain accurate.
