human typically eats a
meal followed by a period of fasting. The amount of energy consumed
during a meal is often 100 times greater than the energy needed for the
duration of the meal. This way humans can live without having to nibble
The human body knows different ways to make sure that
the supply of energy and the blood sugar level remains steady.
Influenced by different hormones the body will switch from one way of
producing energy to the other.
The body knows of 4
different ways to produce energy. The 4 ways are used one after the
other but not in a strictly sequential way. In practice some of these
processes occur simultaneously.
below the time after the consumption of a meal is divided in 4 periods,
and for each period the processes are described that occur at that
A process that ends in "-lysis" is a process that breaks something down. These processes yield energy.
process that ends in "-genesis" is a process that creates something.
These processes cost energy. The end product of such a process is then
used in an other process to break it down for energy.
In the next pages each of these processes is explained. It is also indicated what goes wrong in patients with MCAD deficiency.
is an overview:
- Just after eating –
0 to 3 hours after the meal:
Glycolysis: breaking down sugars (glucose) from the meal for energy.
Glycogenesis: if the supply of glucose exceeds the demand, glycogen is created and stored for later use.
about glycolysis and glycogenesis >
- Fasting state – 12 hours to 2
days after the meal:
the creation of glucose from other substances. This glucose can then be broken down for energy using glycolysis.
Read more about gluconeogenesis >
- Starvation state – a few days to a few
weeks after the meal:
Ketogenesis: the creation of ketones that can be broken down for energy.
about ketogenesis >
times indicated are
only approximately. A lot depends on the amount of calories in the
meal, the level of activity of the person and the speed of the
metabolism of the person.
processes for supplying energy are discussed. All the other biochemical
processes (build up tissue, muscle movements, maintenance etc.) that
are continuously going on in the human body are left aside.