CSSD Practice Exam 2025 – Complete Study Resource

The thermic effect of food (TEF) is the correct choice because it generally accounts for a relatively small portion of total energy expenditure when compared to physical activity and resting metabolic rate. TEF refers to the energy required to digest, absorb, and metabolize food. While it does contribute to overall energy expenditure, its impact is typically less significant than that of physical activity and resting metabolic rate, which are much larger variables.

Resting metabolic rate represents the energy expenditure for basic physiological functions at rest, and it usually constitutes the largest segment of total daily energy expenditure. Physical activity encompasses the calories burned during all forms of movement and exercise, which can vary significantly from person to person based on lifestyle and fitness level.

Cognitive load, while it does involve energy use in the brain, generally exerts a minimal effect on total energy output compared to the other factors. In contrast, TEF remains relatively stable across individuals and does not sharply increase or decrease based on factors like exercise intensity or variability in daily activity levels.

In summary, TEF's contribution to energy output is smaller compared to the significant impacts of physical activity and resting metabolic rate, resulting in it affecting energy output the least among the given factors.