Have you ever wondered how many calories your body needs daily to perform essential functions like breathing, circulating blood, regulating body temperature, and other involuntary processes? This baseline level of calorie expenditure is known as your basal metabolic rate (BMR). Understanding your BMR can provide useful insights into your body’s fundamental energy requirements and help you meet your health and fitness goals.
[1]Your BMR represents the minimum number of calories your body requires to sustain vital bodily processes while at complete rest. It accounts for approximately 60-75% of the total calories you burn daily. The harder your body has to work to maintain normal function, the higher your BMR will be.
Knowing your BMR allows you to estimate your total daily energy expenditure based on your activity levels. If your calorie intake consistently exceeds the amount of energy your body uses, you will gain weight. Conversely, you will lose weight if your calorie intake exceeds your daily expenditure. So calculating your BMR gives you a starting point to determine your caloric needs for weight loss, gain, or maintenance.
How is Basal Metabolic Rate Measured?
To accurately measure BMR, your body must rest completely in a neutral thermal environment after fasting for 12 hours. This ensures your digestive system is inactive and no additional calories are used to process food.
Under these strict conditions, BMR is determined by measuring oxygen consumption and carbon dioxide production. The amount of oxygen you use, and carbon dioxide you expel reflects your body’s metabolism and energy expenditure.
Specialized equipment like a metabolic cart is required to assess respiratory gases and calculate BMR directly. However, several equations can estimate closely using age, sex, height, and weight.
The most well-known BMR formula is the Harris-Benedict equation, which has separate calculations for men and women:
Men: BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) – (5.677 x age in years)
Women: BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) – (4.330 x age in years)
What Factors Influence Basal Metabolic Rate?
Many factors contribute to your BMR, including:
Body Size and Composition: People with muscle mass have higher BMRs because muscle tissue is metabolically active at rest. Fat mass also impacts BMR but to a lesser extent.
Age: BMR steadily declines after age 20 at about 2% per decade. This is likely due to loss of muscle mass as we age.
Sex: Men generally have higher BMRs than women, mostly attributed to men having less body fat and more muscle mass on average.
Genetics: Some inherited traits like muscle fiber type can raise or lower your metabolic rate.
Climate: Colder environments may slightly increase BMR from your body working harder to maintain optimal temperature.
Diet and Eating Patterns: Severe calorie restriction or starvation can decrease BMR by 30%. Fasting and very low-calorie diets are not recommended.
Thyroid Function: An overactive or underactive thyroid directly influences BMR and can raise or lower your metabolic rate beyond normal for your size and age.
As you can see, BMR gives us important clues into how our bodies uniquely function. Tracking your BMR over time can also reveal the metabolic effects of lifestyle changes like exercise, diet, and stress levels.
How to Increase Basal Metabolic Rate
The good news is there are healthy ways to give your BMR a boost:
– Build Lean Muscle with Strength Training: Muscle is metabolically active tissue that burns more calories around the clock.
– Eat More Protein: Consuming adequate protein signals your body to maintain and build calorie-burning muscle mass.
– Avoid Severe Calorie Restriction: Very low-calorie diets can cause adaptive thermogenesis and muscle loss, slowing metabolism.
– Manage Stress: Chronic stress increases cortisol, which may decrease muscle mass and lower BMR over time.
– Get Enough Sleep: Lack of sleep can disrupt metabolic-regulating hormones like ghrelin and leptin.
– Stay Hydrated: Even mild dehydration has been shown to lower BMR. Drink enough fluids daily.
An increased BMR’s potential downside is that it raises your daily caloric needs. However, exercise and adequate protein intake can elevate your metabolism and achieve a healthy, lean physique. Consider using protein-rich supplements to improve your overall health and BMR.
How to Calculate Your Total Daily Energy Expenditure
Once you know your BMR, you can factor in the thermic effect of food (TEF) and your activity level to determine total daily energy expenditure (TDEE).
TEF is the energy used to digest, absorb, and metabolize the macronutrients from food and beverages. It typically accounts for about 10% of your total energy expenditure.
Activity levels are quantified using metabolic equivalents (METs) that estimate how much harder you work than resting. For most healthy adults:
– Sedentary = 1.2 x BMR
– Light activity = 1.375 x BMR
– Moderate activity = 1.55 x BMR
– Very active = 1.725 x BMR
– Extremely active = 1.9 x BMR
Here is an example TDEE calculation for a 40-year older woman:
BMR: 1400 calories
TEF: 140 calories (10% of BMR)
Activity Level: Very Active (1.725)
TDEE = (BMR + TEF) x Activity Multiplier
TDEE = (1400 + 140) x 1.725 = 2,656 calories
This hypothetical woman would need to consume around 2,656 calories daily to maintain her current weight if she follows a very active lifestyle. She would aim to eat 500 calories less than her TDEE to lose one pound per week or about 1,965 calories daily.
Tracking Your Progress
Monitoring your BMR, TEF, activity levels, and current weight over several months can show how many calories your unique body requires. Make modest calorie or activity adjustments and reassess your progress after a few weeks.
Patience is critical – your metabolism may take time to respond to changes in exercise, nutrition, and lifestyle. Stay consistent and be kind to yourself. Achieving your health goals requires commitment, but you should feel free of punishment.
The takeaway? Understanding your basal metabolic rate provides insight into the basic inner workings of your body. While BMR is influenced by factors outside your control, like age and genetics, you can also actively raise your metabolic rate through diet, activity, and self-care. So get moving, eat well, and rest up – your body will thank you by burning more calories!
