On Wed, 27 Oct 2004 21:43:42 -0700, Jay Tanzman
posted:



Dunne E. Dawe wrote:

On 19 Oct 2004 09:59:56 -0700, (tcomeau) posted:


This calorie thing. By what mechanism does the body recognize an
excess of calories and by what mechanism does the body then trigger
fat storage.


Excess energy-containing molecules are detected by their presence
when all energy requirements are satisfied.

In the context of the question, I disagree with this part of your answer. The
body doesn't directly "recognize" an excess of calories to "trigger" fat
storage.

That's what I was trying to say. The body detects an excess of this or
that molecular species. The energy content in calories is our
assessment of the situation. The body just does what it is programmed
to with each particular species.

After a meal, most of the fat in the meal is carried in chylomicrons
to fat cells, where the triglyceride is separated from the chylomicron and
stored in the fat cell. This is a response to the presence of chylomicrons in
the blood, rather than to an "excess of calories."

Yes, the chylomicron can be regarded as a big molecular specie.

Later, as blood glucose
levels drop, fat cells release fatty acids in response to increased glucogon
levels.

And this glucagon is triggered by the dearth of glucose molecules (or,
from an energy chemists point of view, energy)

So, _net_ fat storage is a consequence of a positive energy
imbalance, but almost all dietary fat is initially stored in fat cells
following a meal.

But is burned into energy every day in the vast majority of folk.

My point was that the body doesn't detect energy content, per se, just
molecular species and their greater or lesser abundance in the
circulation.