Which statement best describes the relationship between BMR and body size in children?

Which statement best describes the relationship between BMR and body size in children?

• A. BMR is not related to body size.
• B. BMR is closely related to the proportion of surface area to body mass.
• C. BMR depends only on age.
• D. BMR depends only on activity level.

Answer: (B)

Basal metabolic rate reflects the energy needed to support basic body functions, and in children this demand scales with how body size relates to surface area. The amount of heat that must be produced to keep the body at a normal temperature depends on surface area, so a higher surface-area-to-mass ratio means more energy per unit of body weight is required. That’s why younger, smaller children, who have a larger surface area relative to their mass, typically have a higher BMR per kilogram, while as they grow, the surface-area-to-mass ratio decreases and BMR per kilogram declines even though total BMR increases with overall size. Thus, the best description is that BMR is closely related to the proportion of surface area to body mass. The other statements don’t capture this sizing effect, since age alone or activity level alone doesn’t explain the relationship between body size and resting energy needs.

Basal metabolic rate reflects the energy needed to support basic body functions, and in children this demand scales with how body size relates to surface area. The amount of heat that must be produced to keep the body at a normal temperature depends on surface area, so a higher surface-area-to-mass ratio means more energy per unit of body weight is required. That’s why younger, smaller children, who have a larger surface area relative to their mass, typically have a higher BMR per kilogram, while as they grow, the surface-area-to-mass ratio decreases and BMR per kilogram declines even though total BMR increases with overall size. Thus, the best description is that BMR is closely related to the proportion of surface area to body mass. The other statements don’t capture this sizing effect, since age alone or activity level alone doesn’t explain the relationship between body size and resting energy needs.