Energy expenditure

Energy expenditure refers to the amount of energy that a person uses to carry out physical functions such as breathing, circulating blood, digesting food, or physical movement. It is usually measured in calories.

Overview

Energy expenditure is a critical component of energy balance, which is the balance between the amount of energy consumed and the amount of energy expended. When energy intake exceeds energy expenditure, the result is weight gain. Conversely, when energy expenditure exceeds energy intake, the result is weight loss.

Components of Energy Expenditure

Energy expenditure can be divided into three main components:

1. Basal metabolic rate (BMR): This is the amount of energy required to maintain the body's basic physiological functions while at rest. It accounts for about 60-75% of total energy expenditure.
2. Physical activity: This includes both planned exercise and spontaneous physical activity. It accounts for about 15-30% of total energy expenditure.
3. Thermic effect of food (TEF): This is the energy required to digest, absorb, and metabolize nutrients in food. It accounts for about 10% of total energy expenditure.

Factors Affecting Energy Expenditure

Several factors can affect a person's energy expenditure, including:

1. Age: Energy expenditure generally decreases with age due to a decrease in lean body mass and an increase in fat mass.
2. Gender: Men generally have a higher energy expenditure than women due to their larger size and greater muscle mass.
3. Body composition: Lean body mass, which includes muscle, bone, and organs, has a higher metabolic rate than fat mass.
4. Physical activity level: The more active a person is, the higher their energy expenditure.
5. Diet: Certain foods can increase energy expenditure due to their thermic effect.

Measurement of Energy Expenditure

There are several methods to measure energy expenditure, including:

1. Indirect calorimetry: This method measures the amount of oxygen consumed and carbon dioxide produced to estimate energy expenditure.
2. Doubly labeled water: This method measures the difference in the rate of elimination of two isotopes, oxygen-18 and deuterium, to estimate energy expenditure.
3. Heart rate monitoring: This method uses the relationship between heart rate and oxygen consumption to estimate energy expenditure.

See Also

• Basal metabolic rate
• Physical activity
• Thermic effect of food
• Indirect calorimetry
• Doubly labeled water
• Heart rate monitoring

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