Thermogenesis
Encyclopedia
Thermogenesis is the process of heat
production in organisms. It occurs mostly in warm-blooded
animals, but a few species of thermogenic plants
exist.
s, thermogenic methods can be classified as one of the following:
. It produces heat because the conversion of the chemical energy of ATP
into kinetic energy
causing some of the energy to show up as heat. It is not 100% efficient. No real movement is produced in shivering because opposing (antagonistic
) muscle pairs are activated at the same time resulting in the shivering.
(brown fat) that is present in human infants, and hibernating mammal
s. Non-shivering thermogenesis can be obligatory or facultative. Obligatory thermogenesis is the heat production automatically caused by the metabolic rate, while facultative thermogenesis can be activated in cold exposure to raise body temperature.
In this process, substances such as free fatty acids (derived from triacylglycerols) remove purine (ADP, GDP and others) inhibition of thermogenin
(uncoupling protein
-1), which causes an influx of H+ into the matrix of the mitochondria and bypasses the ATP synthase
channel. This uncouples oxidative phosphorylation
, and the energy from the proton motive force is dissipated as heat
rather than producing ATP from ADP, which would store chemical energy for the body's use. Thermogenesis can also be produced by leakage of the sodium-potassium pump
and the Ca2+ pump. Thermogenesis is contributed to by futile cycle
s, such as the simultaneous occurrence of lipogenesis
and lipolysis
or glycolysis
and gluconeogenesis
.
The low demands of thermogenesis mean that free fatty acids draw, for the most part, on lipolysis
as the method of energy production.
and the sympathetic nervous system
. Some hormones, such as norepinephrine
and leptin
, may stimulate thermogenesis by activating the sympathetic nervous system. Rising insulin
levels after eating may be responsible for diet-induced thermogenesis (thermic effect of food
).
are commonly made up of ephedra
, bitter orange
, capsicum
, ginger
, guar gum
, and pyruvate. Caffeine
and EGCG
, both found in green tea
, may increase thermogenesis regulated by catecholamine
s such as norepinephrine. Researchers are also investigating the possibility of increasing the amount of brown adipose tissue
in the body, a site of thermogenesis. Leptin
infusions, being studied due to the leptin resistance seen in obesity
, may boost metabolism by stimulating thermogenesis and also reduce hunger and appetite.
Although bodybuilding
formulations comprise the most common use of thermogenics
, the drugs are entering the mainstream dieting
industry.
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
production in organisms. It occurs mostly in warm-blooded
Warm-blooded
The term warm-blooded is a colloquial term to describe animal species which have a relatively higher blood temperature, and maintain thermal homeostasis primarily through internal metabolic processes...
animals, but a few species of thermogenic plants
Thermogenic plants
Thermogenic plants have the ability to raise their temperature above that of the surrounding air. Heat is generated in the mitochondria, as a secondary process of cellular respiration called thermogenesis...
exist.
Types
Depending on whether they are initiated through locomotion and intentional movement of the muscleMuscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
s, thermogenic methods can be classified as one of the following:
- Exercise-associated thermogenesis (EAT)
- Non-exercise activity thermogenesis (NEAT)
- Diet-induced thermogenesisThermic effect of foodThermic effect of food , or TEF in shorthand, is the increment in energy expenditure above resting metabolic rate due to the cost of processing food for storage and use. It is one of the components of metabolism along with the resting metabolic rate, and the exercise component...
(DIT)
Shivering
One method to raise temperature is through shiveringShivering
Shivering is a bodily function in response to early hypothermia in warm-blooded animals. When the core body temperature drops, the shivering reflex is triggered to maintain homeostasis. Muscle groups around the vital organs begin to shake in small movements in an attempt to create warmth by...
. It produces heat because the conversion of the chemical energy of ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
into kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
causing some of the energy to show up as heat. It is not 100% efficient. No real movement is produced in shivering because opposing (antagonistic
Antagonist (muscle)
Most muscles work in pairs, and when a muscle works it needs to have an agonist and an antagonist, unless the muscle's natural state is opposite to that which is produced by the muscle, example Sphincter ani externus muscle....
) muscle pairs are activated at the same time resulting in the shivering.
Non-shivering thermogenesis
Non-shivering thermogenesis usually occurs in brown adipose tissueBrown adipose tissue
Brown adipose tissue or brown fat is one of two types of fat or adipose tissue found in mammals....
(brown fat) that is present in human infants, and hibernating mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s. Non-shivering thermogenesis can be obligatory or facultative. Obligatory thermogenesis is the heat production automatically caused by the metabolic rate, while facultative thermogenesis can be activated in cold exposure to raise body temperature.
In this process, substances such as free fatty acids (derived from triacylglycerols) remove purine (ADP, GDP and others) inhibition of thermogenin
Thermogenin
Thermogenin is an uncoupling protein found in the mitochondria of brown adipose tissue . It is used to generate heat by non-shivering thermogenesis...
(uncoupling protein
Uncoupling protein
An uncoupling protein is a mitochondrial inner membrane protein that can dissipate the proton gradient before it can be used to provide the energy for oxidative phosphorylation.There are five types known in mammals:* UCP1, also known as thermogenin* UCP2...
-1), which causes an influx of H+ into the matrix of the mitochondria and bypasses the ATP synthase
ATP synthase
right|thumb|300px|Molecular model of ATP synthase by X-ray diffraction methodATP synthase is an important enzyme that provides energy for the cell to use through the synthesis of adenosine triphosphate . ATP is the most commonly used "energy currency" of cells from most organisms...
channel. This uncouples oxidative phosphorylation
Oxidative phosphorylation
Oxidative phosphorylation is a metabolic pathway that uses energy released by the oxidation of nutrients to produce adenosine triphosphate . Although the many forms of life on earth use a range of different nutrients, almost all aerobic organisms carry out oxidative phosphorylation to produce ATP,...
, and the energy from the proton motive force is dissipated as heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
rather than producing ATP from ADP, which would store chemical energy for the body's use. Thermogenesis can also be produced by leakage of the sodium-potassium pump
Na+/K+-ATPase
Na+/K+-ATPase is an enzyme located in the plasma membrane in all animals.- Sodium-potassium pumps :Active transport is responsible for cells containing relatively high...
and the Ca2+ pump. Thermogenesis is contributed to by futile cycle
Futile cycle
A futile cycle, also known as a substrate cycle, occurs when two metabolic pathways run simultaneously in opposite directions and have no overall effect other than to dissipate energy in the form of heat...
s, such as the simultaneous occurrence of lipogenesis
Lipogenesis
Lipogenesis is the process by which acetyl-CoA is converted to fats. The former is an intermediate stage in metabolism of simple sugars, such as glucose, a source of energy of living organisms. Through lipogenesis, the energy can be efficiently stored in the form of fats...
and lipolysis
Lipolysis
Lipolysis is the breakdown of lipids and involves the hydrolysis of triglycerides into free fatty acids followed by further degradation into acetyl units by beta oxidation. The process produces Ketones, which are found in large quantities in ketosis, a metabolic state that occurs when the liver...
or glycolysis
Glycolysis
Glycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+...
and gluconeogenesis
Gluconeogenesis
Gluconeogenesis is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as lactate, glycerol, and glucogenic amino acids....
.
The low demands of thermogenesis mean that free fatty acids draw, for the most part, on lipolysis
Lipolysis
Lipolysis is the breakdown of lipids and involves the hydrolysis of triglycerides into free fatty acids followed by further degradation into acetyl units by beta oxidation. The process produces Ketones, which are found in large quantities in ketosis, a metabolic state that occurs when the liver...
as the method of energy production.
Regulation
Non-shivering thermogenesis is regulated mainly by thyroid hormoneThyroid hormone
The thyroid hormones, thyroxine and triiodothyronine , are tyrosine-based hormones produced by the thyroid gland primarily responsible for regulation of metabolism. An important component in the synthesis of thyroid hormones is iodine. The major form of thyroid hormone in the blood is thyroxine ,...
and the sympathetic nervous system
Sympathetic nervous system
The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...
. Some hormones, such as norepinephrine
Norepinephrine
Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter...
and leptin
Leptin
Leptin is a 16 kDa protein hormone that plays a key role in regulating energy intake and energy expenditure, including appetite and metabolism. It is one of the most important adipose derived hormones...
, may stimulate thermogenesis by activating the sympathetic nervous system. Rising insulin
Insulin
Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....
levels after eating may be responsible for diet-induced thermogenesis (thermic effect of food
Thermic effect of food
Thermic effect of food , or TEF in shorthand, is the increment in energy expenditure above resting metabolic rate due to the cost of processing food for storage and use. It is one of the components of metabolism along with the resting metabolic rate, and the exercise component...
).
Potential use in obesity
As a significant component of the metabolic rate, thermogenesis can potentially be stimulated to increase energy expenditure and fat oxidation. ThermogenicsThermogenics
Thermogenic means tending to produce heat and is commonly applied to drugs which increase heat through metabolic stimulation or to microorganisms which create heat within organic waste....
are commonly made up of ephedra
Ephedra
Ephedra refers to the plant Ephedra sinica. E. sinica, known in Chinese as ma huang , has been used in traditional Chinese medicine for 5,000 years for the treatment of asthma and hay fever, as well as for the common cold...
, bitter orange
Bitter orange
The name "bitter orange", also known as Seville orange, sour orange, bigarade orange, and marmalade orange, refers to a citrus tree and its fruit. Many varieties of bitter orange are used for their essential oil, which is used in perfume and as a flavoring...
, capsicum
Capsicum
Capsicum is a genus of flowering plants in the nightshade family, Solanaceae. Its species are native to the Americas where they have been cultivated for thousands of years, but they are now also cultivated worldwide, used as spices, vegetables, and medicines - and have become are a key element in...
, ginger
Ginger
Ginger is the rhizome of the plant Zingiber officinale, consumed as a delicacy, medicine, or spice. It lends its name to its genus and family . Other notable members of this plant family are turmeric, cardamom, and galangal....
, guar gum
Guar gum
Guar gum, also called guaran, is a galactomannan. It is primarily the ground endosperm of guar beans. The guar seeds are dehusked, milled and screened to obtain the guar gum. It is typically produced as a free-flowing, pale, off-white-colored, coarse to fine ground powder.-Production:Guar gum is an...
, and pyruvate. Caffeine
Caffeine
Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants...
and EGCG
Epigallocatechin gallate
Epigallocatechin gallate , also known as epigallocatechin 3-gallate, is the ester of epigallocatechin and gallic acid, and is a type of catechin....
, both found in green tea
Green tea
Green tea is made solely from the leaves of Camellia sinensis that have undergone minimal oxidation during processing. Green tea originates from China and has become associated with many cultures throughout Asia. It has recently become more widespread in the West, where black tea is traditionally...
, may increase thermogenesis regulated by catecholamine
Catecholamine
Catecholamines are molecules that have a catechol nucleus consisting of benzene with two hydroxyl side groups and a side-chain amine. They include dopamine, as well as the "fight-or-flight" hormones adrenaline and noradrenaline released by the adrenal medulla of the adrenal glands in response to...
s such as norepinephrine. Researchers are also investigating the possibility of increasing the amount of brown adipose tissue
Brown adipose tissue
Brown adipose tissue or brown fat is one of two types of fat or adipose tissue found in mammals....
in the body, a site of thermogenesis. Leptin
Leptin
Leptin is a 16 kDa protein hormone that plays a key role in regulating energy intake and energy expenditure, including appetite and metabolism. It is one of the most important adipose derived hormones...
infusions, being studied due to the leptin resistance seen in obesity
Obesity
Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems...
, may boost metabolism by stimulating thermogenesis and also reduce hunger and appetite.
Although bodybuilding
Bodybuilding
Bodybuilding is a form of body modification involving intensive muscle hypertrophy. An individual who engages in this activity is referred to as a bodybuilder. In competitive and professional bodybuilding, bodybuilders display their physiques to a panel of judges, who assign points based on their...
formulations comprise the most common use of thermogenics
Thermogenics
Thermogenic means tending to produce heat and is commonly applied to drugs which increase heat through metabolic stimulation or to microorganisms which create heat within organic waste....
, the drugs are entering the mainstream dieting
Dieting
Dieting is the practice of eating food in a regulated fashion to achieve or maintain a controlled weight. In most cases dieting is used in combination with physical exercise to lose weight in those who are overweight or obese. Some athletes, however, follow a diet to gain weight...
industry.