Daily energy expenditure
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Components of Daily Energy Expenditure: Resting Metabolic Rate, Thermic Effect, and Activity
Daily energy expenditure (DEE) is made up of three main components: resting metabolic rate (RMR), the thermic effect of food (TEF), and activity energy expenditure (AEE) 45. RMR, which is the energy used to maintain basic body functions at rest, accounts for about 60-75% of DEE. TEF, the energy used to digest and process food, makes up about 10%. AEE, which includes all physical activity from exercise and daily movements, is the most variable part and can range from 15-30% of DEE .
Variability in Daily Energy Expenditure: The Role of Nonexercise Activity
While RMR and TEF are relatively stable and reproducible, most of the variation in DEE between people comes from differences in nonexercise activity, such as fidgeting, posture changes, and other spontaneous movements 1710. Factors like occupation, environment, genetics, age, gender, and body composition can influence nonexercise activity, but the exact impact of each is not fully understood 110. Studies show that even after accounting for body size, spontaneous physical activity can account for a large portion of the differences in daily energy use between individuals .
Body Composition and Age: Key Determinants of Energy Expenditure
Fat-free mass (FFM) is the strongest predictor of DEE, explaining a large part of the differences between individuals 2678. As people age, DEE changes: it is highest in infants, declines through childhood and adolescence, remains stable in adulthood, and decreases again in older age 24. Age and FFM together can explain much of the variation in DEE among healthy adults .
Physical Activity and Its Impact on Energy Expenditure
Physical activity is a major driver of DEE variability. The energy spent on activity is influenced by genetics, lifestyle, and health status . In young adults, exercise training does not always increase total activity energy expenditure, as non-training activity may decrease to compensate. In older adults, exercise training can lead to a compensatory drop in other daily activities, making it hard to increase total energy expenditure through exercise alone . Activity energy expenditure is also an independent predictor of how much food people eat each day, showing that both metabolic and behavioral components of DEE can influence energy intake .
Gender, Obesity, and Daily Energy Expenditure
When adjusted for FFM, women may have higher DEE than men, likely due to higher physical activity levels . DEE is also inversely related to age and increases with body mass index (BMI) . Low nonbasal energy expenditure (energy spent outside of basic body functions) is linked to higher body fatness, suggesting that low activity levels can contribute to obesity .
Measurement and Reproducibility of Daily Energy Expenditure
DEE and its components are measured using methods like indirect calorimetry and doubly labeled water, which provide reliable and reproducible results 147. The coefficient of variation is lowest for exercise energy expenditure, followed by RMR, 24-hour energy expenditure, and TEF, indicating that these measures are consistent over time .
Conclusion
Daily energy expenditure is determined by a combination of resting metabolic rate, the thermic effect of food, and activity energy expenditure. While RMR and TEF are stable, most of the variability in DEE comes from differences in physical activity, especially nonexercise movements. Body composition, age, gender, and lifestyle all play important roles in shaping individual energy needs. Understanding these factors is essential for developing effective nutrition and health strategies across the lifespan.
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