The main issue is body composition (see the body fat calculator for more). Calorie expenditure will vary depending on the ratio of body fat to muscle or lean mass. NOTE that as our bodies adapt to exercise and our body composition changes - so will the amount of Calories burned.
The definition of a throttle is a valve that controls the fluid flow. An example of a throttle is a car part that controls how fuel moves through the system. Throttle is defined as to control the speed of an engine or the flow of fuel in an engine, or to hold down or choke.
One of the few reasons to change to an aftermarket throttle body is performance. The throttle body is a common bottle neck that may restrict air flow. This restriction comes from one of two places. The engine has had upgrades or some kind that allow it to breath better.