Basal Metabolic rate

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Physical activity is known to consume energy, but most of us are unaware that energy is expended even during non-activity hours. This is termed as basal metabolic rate.

What is Basal Metabolic Rate? 

Basal Metabolic Rate (BMR) is defined as the energy expenditure rate of an individual while at rest. Simply put, the amount of calories burnt at rest determines the basal metabolic rate.

The basal metabolic rate is the energy required when the body and the digestive system are resting in a temperate environment.

Energy will only be used to maintain vital organs such as the heart, lungs, nervous system, kidneys, liver, intestines, lungs, muscles and skin in a proper functioning state.

For most people, the normal daily activity requirement is about 70% of total energy (calories) each day. Physical activity accounts for nearly 20% of expenditure, while digestion accounts for about 10%.

Functions of basal metabolic rate 

The BMR accounts for approximately 60-70 per cent of the calories we burn or expend. This includes the energy that the body expends to maintain the functions of our body, such as:

  • Heartbeat
  • Cell production
  • Respiration
  • Maintenance of body temperature
  • Blood circulation
  • Nutrient processing

Breathing 

Breathing involves chemical and biological processes to deliver oxygen to the body’s cells and expel carbon dioxide out of the body. This process is continuous and requires energy. Breathing thereby influences BMR.

Circulation

Blood circulation transports essential nutrients and oxygen to the cells making use of energy. The process also eliminates wastes from the cells, increasing the BMR.

Nutrient processing

Digestion of food requires breaking down the nutrients by utilising energy. 

Cell production 

According to an NCBI book, cells require a constant supply of energy to maintain the body’s biological functioning that keeps a person alive.

This energy is obtained from the chemical bond energy in food molecules and is used to power cells. This has an effect on BMR.

How do you calculate your basal metabolic rate?

The BMR is measured while awake under certain conditions. A person’s sympathetic nervous system must be inactive for an accurate BMR measurement, which means the person must be completely rested.

Basal metabolism accounts for the majority of a person’s total energy needs. The daily calorie requirement is calculated by multiplying the BMR value by a factor ranging from 1.2 to 1.9, depending on activity level.

The basal metabolic rate is calculated using the following formulas.

Mifflin-St Jeor equation:

  • Men

BMR = 10 (Body weight in Kg) + 6.25 (Height in cm) – 5 (Age) + 5

  • Women

BMR = 10 (Body weight in Kg) + 6.25 (Height in cm) – 5 (Age) – 161

Harris-Benedict Equation: 

  • Men

BMR = 66.4730 + 13.7516 (weight in kg) + 5.0033 (height in cm) – 6.7550 (age in years)

  • Women

BMR = 655.0955 + 9.5634 (weight in kg) + 1.8496 (height in cm) – 4.6756 (age in years)

What affects your basal metabolic rate? 

Multiple factors influence a person’s BMR, including:

  • Body size: The metabolising tissues are more in an adult with larger body size, thereby increasing the BMR.
  • Body fat percentage:  A large number of fat cells burns far fewer calories, lowering the BMR.
  • Starvation or fasting: Consuming very few calories causes the body to slow its metabolism in order to conserve energy. BMR can drop by up to 15% during such times, and if lean muscle tissue is lost, BMR is further reduced.
  • Age: As a person ages, the metabolism rate slows down as a result of muscle tissue loss. Hormonal and neurological changes also trigger this.
  • Height: Due to the energy requirement during the growth phase and the extra energy required to maintain the body temperature, infants and children have higher energy demands per unit of body weight.
  • Weight: Higher the weight, the higher the BMR.
  • Gender: Men have faster metabolism compared to women owing to their large body size and muscle mass.
  • Genetic factors: The metabolic rate may be determined partly by genes.
  • Hormonal control: BMR is regulated by hormonal and nervous systems. Hormonal imbalances can impact how quickly or slowly the body burns calories.
  • Temperature: If the temperature is extremely low or extremely high, the body must work harder to maintain its normal body temperature, which raises BMR.
  • Body composition: Body composition comprises lean muscle and lean body mass. People with increased lean body mass tend to burn a lot of calories in comparison to a person with a similar weight but with an increased body fat content.
  • Infections or illnesses: Illness causes an increase in BMR since the body has to work more to build new tissues and trigger an immune response.
  • Physical activity: Tough muscles require a lot of energy to burn. Regular exercise builds muscle and makes the body burn calories faster, even during rest.
  • Drugs: Even substances like caffeine and nicotine can increase the BMR.
  • Nutritional deficiencies: Certain dietary deficiencies are known to slow the metabolism.

How to estimate your BMR?  

BMR is estimated by using Mifflin-St Jeor or Harris-Benedict equation. The calculation requires the height, weight and age to estimate the basal metabolic rate.

Why do you want to know your BMR? 

Knowing the basal metabolic rate is significant for losing, maintaining or gaining weight. 

An individual’s BMR helps determine the amount of calories one should eat to meet the daily requirement.

To lose weight, one must take fewer calories than their BMR. Also, knowing the basal metabolic rate is critical regardless of a person’s nutrition, fitness or weight goals.

How many calories do you need every day? 

The ideal calorie intake varies according to age, metabolism and level of physical activity, among other factors.

Once BMR is calculated, daily calorie requirement is found by multiplying the basal metabolic rate with various activity level factors.

  • Sedentary: Calories = BMR × 1.2
  • Lightly active: Calories = BMR × 1.375
  • Moderately active: Calories = BMR × 1.55
  • Very active: Calories = BMR × 1.725
  • Super active: Calories = BMR × 1.9

How can you change your BMR? 

The basal metabolic rate (BMR) measures how many calories one would burn if a person just rests all day. It’s determined in part by genetics, which cannot be changed. 

However, factors like an individual’s weight can be changed with weight loss or weight gain, changing the BMR.

Use BMR to lose weight

Knowing the BMR can help a person determine their total daily energy expenditure to create a calorie deficit, which is defined as consuming fewer calories than what is burnt for energy each day. Weight loss requires a calorie deficit.

In order to lose weight, one must create a calorie deficit, which means they should either reduce the calorie intake below their total daily energy expenditure or increase the total daily energy expenditure. 

The energy requirements can be calculated by multiplying the BMR by different activity factors to see how the caloric burn changes with increased exercise.

Conclusion 

Basal Metabolic Rate (BMR) help to estimate the minimum calories a person requires to sustain their fundamental life functions while the body is at rest. 

Factors like body size, fat percentage, physical activity, gender, age, height, weight, body composition, heredity, temperature and drugs determine a person’s BMR.

The daily calorie requirement of an individual can be calculated according to their activity level. BMR, in general, cannot be changed. But when physical activity and body composition change, it has an effect on the basal metabolic rate.

FAQs

What can affect the basal metabolic rate? 

Several factors, including age, gender, height, weight, physical activity, body size and body fat percentage, affect the basal metabolic rate.

What is an ideal basal metabolic rate? 

Ideal BMR doesn’t exist. The basal metabolic rate varies with each individual depending on their various personal factors. Calculating basal metabolic rate using a BMR calculator will determine a person’s ideal BMR.

Is it better to have a lower or higher basal metabolic rate? 

An ideal and normal BMR is fine. According to a PMC article, higher BMR was linked to an increased risk of death regardless of age, weight, BMI, social habits, physical activity, strength or muscle mass. 
 People with high BMR can eat enough not to fall short of their daily calorie requirements.
 A low BMR indicates that one must consume fewer calories to lose body fat and weight. It is always better to calculate the BMR using a BMR calculator to know the correct value.

What is a good basal metabolic rate? 

There is no such thing as a good BMR.
BMR of every individual is unique. Age, gender, body size, weight, height and even the size of the internal organs have an impact on the BMR.


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