Hello Flappy,
You have asked a very interesting question. I will provide you an
outline here and you can post additional questions if you need more
details.
Overview: In fasting, the blood sugar (called glucose) will start to
drop but then the body will respond to keep it in the normal range.
The body can keep glucose in the blood by (1) using stored sugar
(called glycogen), and by (2) making new sugar (called
gluconeogenesis). If these processes do not supply enough glucose, the
body will start making an alternate form of energy for the brain and
muscles, the energy comes from ketone bodies made in the liver.
During the first hours of fasting, the blood sugar begins to drop as
glucose gets used up. In response to the low blood sugar, the pancreas
releases a hormone called glucagon. Glucagon signals the liver (and
kidneys) to start breaking down glycogen. This is called glycolysis.
Glycogen is basically a bunch of glucose molecules joined together for
storage. Glycogen gets turned into glucose and released into the
blood.
As the glycogen supplies start to get used up (within about 12 hours),
the liver begins to make glucose in a process called gluconeogenesis.
The liver makes new glucose from uses amino acids, which come from
protein breakdown.
During fasting, fat will also get used for energy but it doesn't get
turned into glucose.
After about 16-32 hours of fasting, the liver begins to turn fats into
ketone bodies. These ketone bodies can be used for energy by muscle
and the brain when there is not a lot enough glucose available.
You can see that the live plays a very key role in maintaining the
body's glucose levels. Through most of fasting, the glucose
concentration in the blood will stay at a pretty normal level.
I hope this is helpful,
RMH
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