Table of contents
Fasting and stress metabolism....................................................................2
1.0 Fast.....................................................................................................2
2.0 The body's energy reserves...............................................................2
2.1 Free amino acid pool..........................................................................3
3.0 Hormonal changes.............................................................................4
4.0 Changes in energy turnover...............................................................5
4.1 Ketones..............................................................................................6
5.0 Stress metabolism..............................................................................7
5.1 Hormonal and inflammatory changes................................................7
5.2 Changes in metabolism......................................................................8
5.3 Protein loss and nitrogen balance....................................................10
5.4 Albumin............................................................................................11
Page 1of 11
, Fasting and stress metabolism
1.0 Fast
Fasting is abstinence from food and possibly liquid intake for semi-fasting,
which denotes a situation where the body is not supplied with sufficient
nutrients to maintain the balance between anabolic and catabolic
processes, whereby the catabolic biochemical processes dominate.
The fasting period begins when you have taken your last bite/sip. We will
not talk about fasting metabolism until the situation where the hormonally
conditioned catabolic fasting reactions occur.
It has been shown that fasting itself contributes to postoperative insulin
resistance and thus has a negative impact on anabolic processes and
recovery.
2.0 The body's energy reserves
Fat mass is the body's largest and actual energy reserve. Fat is stored in
fat cells, adipocytes, in the form of triglycerides. A triglyceride is a fat
molecule that consists of three fatty acids bound together by glycerol. A
triglyceride contains 37 kJ/g, but adipose tissue also contains a small
amount of water, protein and electrolytes intra- and extracellularly, which
is why the calorific value of adipose tissue is slightly lower, approximately
32 kJ/g.
The body also has a small depot of carbohydrate, glucose. Glucose can be
stored as glycogen in the muscles and liver. In adults, the muscles can
store about 300-600 g of glycogen, but this can only be used for muscle
work and cannot be released into circulation in the blood.
The liver can store about 70-120 g of glycogen, which can be converted to
glucose via glycogenolysis. Under normal conditions, the body's total
glycogen content is no more than about 400 g. Glucose from the liver can
be released into the blood and thereby help maintain a stable level of
blood glucose. The glucose is sent around the body with the blood and
can be absorbed by the body's glucose-requiring tissues. One gram of
glucose from the body's depots provides 17 kJ/g.
There is no specific "protein depot" in the body, because all protein is part
of the cell mass in muscles, organs, enzymes, transport proteins in the
blood, etc. In addition, there is always a small amount of free amino acids
Page 2of 11
Fasting and stress metabolism....................................................................2
1.0 Fast.....................................................................................................2
2.0 The body's energy reserves...............................................................2
2.1 Free amino acid pool..........................................................................3
3.0 Hormonal changes.............................................................................4
4.0 Changes in energy turnover...............................................................5
4.1 Ketones..............................................................................................6
5.0 Stress metabolism..............................................................................7
5.1 Hormonal and inflammatory changes................................................7
5.2 Changes in metabolism......................................................................8
5.3 Protein loss and nitrogen balance....................................................10
5.4 Albumin............................................................................................11
Page 1of 11
, Fasting and stress metabolism
1.0 Fast
Fasting is abstinence from food and possibly liquid intake for semi-fasting,
which denotes a situation where the body is not supplied with sufficient
nutrients to maintain the balance between anabolic and catabolic
processes, whereby the catabolic biochemical processes dominate.
The fasting period begins when you have taken your last bite/sip. We will
not talk about fasting metabolism until the situation where the hormonally
conditioned catabolic fasting reactions occur.
It has been shown that fasting itself contributes to postoperative insulin
resistance and thus has a negative impact on anabolic processes and
recovery.
2.0 The body's energy reserves
Fat mass is the body's largest and actual energy reserve. Fat is stored in
fat cells, adipocytes, in the form of triglycerides. A triglyceride is a fat
molecule that consists of three fatty acids bound together by glycerol. A
triglyceride contains 37 kJ/g, but adipose tissue also contains a small
amount of water, protein and electrolytes intra- and extracellularly, which
is why the calorific value of adipose tissue is slightly lower, approximately
32 kJ/g.
The body also has a small depot of carbohydrate, glucose. Glucose can be
stored as glycogen in the muscles and liver. In adults, the muscles can
store about 300-600 g of glycogen, but this can only be used for muscle
work and cannot be released into circulation in the blood.
The liver can store about 70-120 g of glycogen, which can be converted to
glucose via glycogenolysis. Under normal conditions, the body's total
glycogen content is no more than about 400 g. Glucose from the liver can
be released into the blood and thereby help maintain a stable level of
blood glucose. The glucose is sent around the body with the blood and
can be absorbed by the body's glucose-requiring tissues. One gram of
glucose from the body's depots provides 17 kJ/g.
There is no specific "protein depot" in the body, because all protein is part
of the cell mass in muscles, organs, enzymes, transport proteins in the
blood, etc. In addition, there is always a small amount of free amino acids
Page 2of 11
