Physiology of Food Energy Sources and Its Usage in the
Body
The tissue of the body generally uses various energy sources in the body
in proportion to its various concentrations in the bloodstream. For example if glucose in the
bloodstream increases, the human body will prefer usage of glucose to others as energy source. The
same way, if a given energy source decreases in the bloodstream, the human body will prefer using
less of that energy source. When the availability of carbohydrates is decreased, the ketogenic diet
changes the human body to use fats as the primary source of energy.
Glucose is the preferred source of energy for most tissues in the human body. The main exception to
this is the heart which uses a mixture of glucose, ketones and free fatty acids. The main source of
glucose in the body is dietary carbohydrate. However, there are other substances that can be
converted to glucose in the liver and kidney in a process called gluconeogenesis. The substances
include amino acids, glutamine and alanine.
When levels of glucose in the human body are normal, gluconeogenesis in
the body’s protein stores is little. This has led to the assumption by many people that
carbohydrate produces a “sparring effect” by preventing the breakage of protein to glucose.
Well, it is true that a high level of carbohydrate intake can produce a “sparring effect” but is
often ignored that high carbohydrate level also decreases use of fat as energy source. Thus it can
be said that carbohydrate is also “fat sparring”.
In situations when the requirement for glucose is high but availability is
low such as in the initial stages of fasting, the body breaks stores of protein in the body to
produce glucose. This can be the origin of concept that low levels of carbohydrates in the diet
produce a muscle wasting effect in the body.
Adequate amount of protein intake of a ketogenic diet in the first weeks
prevents muscle wasting by supply of amino acids for gluconeogenesis which would have otherwise
come from proteins. The need for gluconeogenesis from protein also decreases in conditions when
glucose is less in the human body due to there being other options being available for energy use
including ketones and free fatty acids. The adaptation of ketogenic diet is from a decrease in
levels of glucose in the human body resulting to a sparring effect.
Free fatty acids are able to be used in the human body as sources of
energy if available. The tissues include the heart, skeletal muscle among others. The tissues
not capable of using free fatty acids and glucose as energy source include the renal medulla,
brain, type II muscle fibers and bone marrow. The biggest misunderstanding about usage of glucose
as the main source of energy for the brain is from the fact the brain in able to use free fatty
acids for fuel. Well, it is true the brain runs on glucose as fuel but it also uses ketones as well
if available.
The brain derives up to 75% of its total energy from ketones. It is
most likely that the ketones exist to provide energy for the brain in times when carbohydrates are
not available. When the levels of ketones are low in the body, negligible amounts of energy are
derived from them to the mentioned tissues but when the levels of ketones increase then the tissues
in the body derive some of their energy requirements from ketones. Research has suggested the
preferred source of energy for most tissues comes from ketones.
|
