Energy Expenditure
Introduction
Energy expenditure refers to the total amount of energy used by the body to
maintain all vital physiological processes and to perform physical activities. Every
human body constantly consumes energy — even when sleeping, resting, or thinking
— because energy is required for muscle contraction, nerve transmission, digestion,
circulation, respiration, and cellular maintenance.
In dietetics, understanding energy expenditure is essential to determine how much
food energy a person requires daily to maintain health, prevent weight gain or loss,
and support body functions efficiently.
The energy we obtain from food in the form of carbohydrates, proteins, and fats is
used to meet these energy needs. Any imbalance between energy intake and energy
expenditure results in changes in body weight — excess intake leads to fat storage
and obesity, while deficiency results in undernutrition or weight loss.
Hence, for dietitians, accurate estimation of energy expenditure helps in planning
individualized diets, maintaining energy balance, and managing conditions such as
obesity, diabetes, and malnutrition.
Components of Total Energy Expenditure (TEE)
Total Energy Expenditure (TEE) is composed of three main components:
1. Basal Metabolic Rate (BMR) / Basal Energy Expenditure (BEE)
This is the minimum energy required to sustain vital body functions such as
breathing, circulation, and temperature regulation at complete rest. It usually
represents 60–75% of total energy expenditure in a sedentary person. (We will
discuss BMR in detail in the next section.)
2. Thermic Effect of Food (TEF)
Also known as diet-induced thermogenesis, this is the energy required for digestion,
absorption, metabolism, and storage of nutrients. When food is eaten, the body uses
some energy to process it. TEF typically contributes about 5–10% of total daily
energy expenditure. Protein has the highest thermic effect (~20–30%), carbohydrates
moderate (~5–10%), and fats the lowest (~0–5%).
3. Physical Activity Energy Expenditure (PAEE)
, This component varies widely depending on individual lifestyle. It includes all
movements — from routine daily activities like walking and cleaning to structured
exercise and sports. Physical activity accounts for 15–30% of TEE in most people. In
highly active individuals, such as athletes, it may even exceed 50%.
In summary:
TEE = BMR + TEF + PAEE
Factors Affecting Energy Expenditure
Energy expenditure is not fixed; it varies from person to person and even from day to
day depending on several physiological and environmental factors.
1. Age
With aging, lean body mass decreases and fat mass increases, resulting in a lower
BMR and overall energy expenditure. Younger individuals generally require more
energy.
2. Gender
Men usually have higher energy expenditure than women because they have greater
muscle mass and lower body fat percentage.
3. Body Composition
Muscle tissue is metabolically more active than fat. Therefore, people with higher
lean mass have greater energy expenditure.
4. Body Size
Larger individuals have a higher surface area and therefore a greater energy cost to
maintain body temperature and metabolic activities.
5. Hormonal Factors
Hormones such as thyroxine, epinephrine, and growth hormone increase metabolic
activity, whereas hypothyroidism lowers it.
6. Physical Activity Level
The more active a person is, the higher the total energy expenditure. Sedentary
lifestyles decrease energy needs significantly.
7. Environmental Temperature
Introduction
Energy expenditure refers to the total amount of energy used by the body to
maintain all vital physiological processes and to perform physical activities. Every
human body constantly consumes energy — even when sleeping, resting, or thinking
— because energy is required for muscle contraction, nerve transmission, digestion,
circulation, respiration, and cellular maintenance.
In dietetics, understanding energy expenditure is essential to determine how much
food energy a person requires daily to maintain health, prevent weight gain or loss,
and support body functions efficiently.
The energy we obtain from food in the form of carbohydrates, proteins, and fats is
used to meet these energy needs. Any imbalance between energy intake and energy
expenditure results in changes in body weight — excess intake leads to fat storage
and obesity, while deficiency results in undernutrition or weight loss.
Hence, for dietitians, accurate estimation of energy expenditure helps in planning
individualized diets, maintaining energy balance, and managing conditions such as
obesity, diabetes, and malnutrition.
Components of Total Energy Expenditure (TEE)
Total Energy Expenditure (TEE) is composed of three main components:
1. Basal Metabolic Rate (BMR) / Basal Energy Expenditure (BEE)
This is the minimum energy required to sustain vital body functions such as
breathing, circulation, and temperature regulation at complete rest. It usually
represents 60–75% of total energy expenditure in a sedentary person. (We will
discuss BMR in detail in the next section.)
2. Thermic Effect of Food (TEF)
Also known as diet-induced thermogenesis, this is the energy required for digestion,
absorption, metabolism, and storage of nutrients. When food is eaten, the body uses
some energy to process it. TEF typically contributes about 5–10% of total daily
energy expenditure. Protein has the highest thermic effect (~20–30%), carbohydrates
moderate (~5–10%), and fats the lowest (~0–5%).
3. Physical Activity Energy Expenditure (PAEE)
, This component varies widely depending on individual lifestyle. It includes all
movements — from routine daily activities like walking and cleaning to structured
exercise and sports. Physical activity accounts for 15–30% of TEE in most people. In
highly active individuals, such as athletes, it may even exceed 50%.
In summary:
TEE = BMR + TEF + PAEE
Factors Affecting Energy Expenditure
Energy expenditure is not fixed; it varies from person to person and even from day to
day depending on several physiological and environmental factors.
1. Age
With aging, lean body mass decreases and fat mass increases, resulting in a lower
BMR and overall energy expenditure. Younger individuals generally require more
energy.
2. Gender
Men usually have higher energy expenditure than women because they have greater
muscle mass and lower body fat percentage.
3. Body Composition
Muscle tissue is metabolically more active than fat. Therefore, people with higher
lean mass have greater energy expenditure.
4. Body Size
Larger individuals have a higher surface area and therefore a greater energy cost to
maintain body temperature and metabolic activities.
5. Hormonal Factors
Hormones such as thyroxine, epinephrine, and growth hormone increase metabolic
activity, whereas hypothyroidism lowers it.
6. Physical Activity Level
The more active a person is, the higher the total energy expenditure. Sedentary
lifestyles decrease energy needs significantly.
7. Environmental Temperature
