Nutrition Science and Everyday Application - beta v 0.1

ENERGY BALANCE: ENERGY IN, ENERGY OUT—YET NOT AS SIMPLE AS IT SEEMS 375
Figure 7.4. Components of energy expenditure and their percent contribution to the total in
sedentary to moderately active people.
BMR can vary widely among individuals. An individual’s lean body mass—made up of organs,
bone, and muscle—is the biggest determinant of BMR, because lean body tissue is more
metabolically active than fat tissue. This means that a muscular person expends more
energy than a person of similar weight with more fat. Likewise, increasing your muscle mass
can cause an increase in your BMR. However, skeletal muscle at rest only accounts for about
18 percent of the total energy expended by lean mass. Most is used to meet the energy
needs of vital organs. The liver and brain, for example, together account for nearly half of
the energy expenditure by lean mass.
Figure 7.5. Energy expenditure of organs.