On Jan 21, 8:54*pm, Prisoner at War wrote:
What does it mean, exactly, when the body is said to become more
efficient at burning fat?

Efficiency refers to how high a yield of some desired output we obtain
relative to some costly inputs to some process. There is always some
frame of reference defined by human values which determine what
efficiency means in that context.

E.g. the efficiency of a computer program is how much calculation it
gets done in a given amount of time. Time is a costly input to the
process, the result is the deisred output. The energy efficiency of
computation is important: we want CPU's to use less electricity, while
still running fast.

The efficiency of an engine is how much work you obtain from the
energy source, such as fuel. The energy that doesn't become work is
wasted as heat.

Heating can be efficient also. Heating a poorly insulated home is less
efficient than heating an insulated one. Maintaining the place at a
given temperature (the benefit) requires more input (energy) if heat
escapes easily. When heat is easily available (basically, is already
the waste from another process), you don't care about heat efficiency.
A big engine can easily heat the interior of a car, even if the car is
poorly insulated. The heat is produced even if you don't use it for
heating, so wasting it doesn't matter.

To be more efficient at burning fat, it means that the body gets rid
of fat (the desired effect of the process) with less effort (the
costly input). Effort consists of diet and exercise.

So the claim that a body is more efficient at burning fat means that
it can shed body fat with less exercise and less dieting effort than
an inefficient body.

But that's semantics...what's the actual physiology??

The actual physiology is fat mobilization. The difficulty in losing
fat isn't actually burning it, but getting it to march out of the fat
cells and into circulation.

Think about it; you could easily consume a pound of butter over the
next week, without putting any of it on as fat. You could not with
equal ease get a pound of fat to leave your adipose tissue,
particularly if you're already lean. But if you could mobilize a pound
of fat, it would be as easily burned off as that pound of butter.