2.4: Total Energy Expenditure
- Page ID
- 156235
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Total energy expenditure (TEE) is the total amount of energy the body uses in a day, and it is made up of three main components (Figure 2.4). The largest portion is the Basal Metabolic Rate (BMR), which accounts for the energy used to maintain basic bodily functions at rest, such as breathing, circulation, and cell production. The second component is the Thermic Effect of Food (TEF), which is the energy required to digest, absorb, and process the nutrients from the food we eat. The third component is Activity Thermogenesis, which includes all physical activity, from structured exercise to daily tasks like walking or cleaning. In some cases, a fourth component called Non-Exercise Activity Thermogenesis (NEAT) is considered separately, which includes spontaneous movements such as fidgeting or posture changes. Together, these components determine how many calories a person burns each day, and they vary based on factors like age, body composition, activity level, and overall health.
Basal Metabolic Rate (BMR)
BMR is a measure of basal energy expenditure each day; the energy needed to maintain vital functions, sustaining metabolic activities of cells and tissues, and maintaining processes such as blood circulation, respiration, gastrointestinal function, and renal function.
Several key factors influence an individual’s BMR, the most significant factors include the following:
- Body size and composition: People with more muscle mass have a higher BMR because muscle tissue burns more calories at rest than fat tissue.
- Age: BMR is highest during periods of rapid growth and generally decreases with age due to a natural loss of muscle mass and hormonal changes.
- Sex: Males typically have a higher BMR than females because they often have more muscle mass and less body fat.
- Genetics: Some people naturally have a faster or slower metabolism due to inherited traits.
- Hormones: Hormones, especially those produced by the thyroid gland play a major role in regulating BMR.
- Health status: Illnesses, fever, or injuries can raise BMR as the body works harder to heal and maintain normal function.
- Environmental temperature: Being in a cold environment can increase BMR slightly as the body works to maintain a stable internal temperature. Tropical climates can also lead to an increase in BMR.
These factors interact in complex ways, and changes in any of them can affect how many calories the body needs to function at rest.
Activity Thermogenesis
Activity thermogenesis is the component of total energy expenditure that includes all the energy used during physical movement. It can be divided into two main parts: exercise activity thermogenesis, which refers to planned and intentional physical activities like running, swimming, or strength training, and non-exercise activity thermogenesis (NEAT), which includes unstructured movements such as walking to class, typing, fidgeting, or doing household chores. Activity thermogenesis varies the most among individuals as a component of daily energy expenditure and can significantly influence total energy expenditure depending on how active a person is. For example, someone with a physically demanding job or a regular exercise routine will have a higher activity-related energy expenditure compared to someone who is mostly sedentary. Because it is a modifiable component, increasing daily physical activity is one of the most effective ways to boost total energy expenditure and support overall health.
Thermic Effect of Food (TEF)
The Thermic Effect of Food, also known as the Specific Dynamic Action, refers to the increase in energy expenditure that occurs after eating, as the body works to digest, absorb, transport, metabolize, and store nutrients. TEF typically accounts for about 5–10% of total daily energy expenditure. Different types of nutrients have varying thermic effects—protein has the highest TEF, requiring more energy to process, followed by carbohydrates, and then fats, which have the lowest TEF. While TEF is a smaller component of total energy expenditure compared to basal metabolic rate or physical activity, it still plays a role in overall metabolism and can be influenced by factors such as meal size, composition, and timing. Eating frequent, balanced meals that include protein can slightly boost TEF and may contribute to energy balance and weight management.