The calorie is a unit of energy. The Calorie is 1,000 calories; that capital C, distinguishing Calorie from calorie, is a long-established scientific convention but is not always understood more widely. Where the context is about food and exercise, the term appears without the capital C; the Calorie is termed the large calorie or kilocalorie — symbols: Cal, kcal — or food calorie, defined as the heat energy involved in warming one kilogram of water by one degree Celsius. The small calorie was defined as the heat energy to raise the temperature of one gram of water — rather than a kilogram — by the same amount. Although both units relate to the metric system, they have been considered obsolete, or deprecated, in scientific usage, since the adoption of the SI system, but the small calorie is still used in laboratory measurements and calculations, with the values thus established being reported in kilocalories. The calorie was first defined by Nicolas Clément in 1824 as a unit of heat energy, it entered French and English dictionaries between 1841 and 1867.
The word comes from Latin calor, meaning'heat'. The small calorie was introduced by Pierre Antoine Favre and Johann T. Silbermann in 1852. In 1879, Marcellin Berthelot introduced the convention of capitalizing the large Calorie to distinguish the senses; the use of the calorie for nutrition was introduced to the American public by Wilbur Olin Atwater, a professor at Wesleyan University, in 1887. The alternate spelling calory is archaic; the energy needed to increase the temperature of a given mass of water by 1 °C depends on the atmospheric pressure and the starting temperature. Accordingly, several different precise definitions of the calorie have been used; the pressure is taken to be the standard atmospheric pressure. The temperature increase can be expressed as one kelvin, which means the same as an increment of one degree Celsius; the two definitions most common in older literature appear to be the 15 °C calorie and the thermochemical calorie. Until 1948, the latter was defined as 4.1833 international joules.
The calorie was first defined to measure energy in the form of heat in experimental calorimetry. In a nutritional context, the kilojoule is the SI unit of food energy, although the kilocalorie is still in common use; the word calorie is popularly used with the number of kilocalories of nutritional energy measured. To avoid confusion, it is sometimes written Calorie to make the distinction, although this is not understood. To facilitate comparison, specific energy or energy density figures are quoted as "calories per serving" or "kilocalories per 100 g". A nutritional requirement or consumption is expressed in calories per day. One gram of fat in food contains nine calories, while a gram of either a carbohydrate or a protein contains four calories. Alcohol in a food contains seven calories per gram. In other scientific contexts, the term calorie always refers to the small calorie. Though it is not an SI unit, it is still used in chemistry. For example, the energy released in a chemical reaction per mole of reagent is expressed in kilocalories per mole.
This use was due to the ease with which it could be calculated in laboratory reactions in aqueous solution: a volume of reagent dissolved in water forming a solution, with concentration expressed in moles per liter, will induce a temperature change in degrees Celsius in the total volume of water solvent, these quantities can be used to calculate energy per mole. It is occasionally used to specify energy quantities that relate to reaction energy, such as enthalpy of formation and the size of activation barriers. However, its use is being superseded by the SI unit, the joule, multiples thereof such as the kilojoule. In the past a bomb calorimeter was utilised to determine the energy content of food by burning a sample and measuring a temperature change in the surrounding water. Today this method is not used in the USA and has been succeeded by calculating the energy content indirectly from adding up the energy provided by energy-containing nutrients of food; the fibre content is subtracted to account for the fact fibre is not digested by the body
An oil is any nonpolar chemical substance, a viscous liquid at ambient temperatures and is both hydrophobic and lipophilic. Oils have a high carbon and hydrogen content and are flammable and surface active; the general definition of oil includes classes of chemical compounds that may be otherwise unrelated in structure and uses. Oils may be animal, vegetable, or petrochemical in origin, may be volatile or non-volatile, they are used for food, medical purposes and the manufacture of many types of paints and other materials. Specially prepared oils are used in some religious rituals as purifying agents. First attested in English 1176, the word oil comes from Old French oile, from Latin oleum, which in turn comes from the Greek ἔλαιον, "olive oil, oil" and that from ἐλαία, "olive tree", "olive fruit"; the earliest attested forms of the word are the Mycenaean Greek, e-ra-wo and, e-rai-wo, written in the Linear B syllabic script. Organic oils are produced in remarkable diversity by plants and other organisms through natural metabolic processes.
Lipid is the scientific term for the fatty acids and similar chemicals found in the oils produced by living things, while oil refers to an overall mixture of chemicals. Organic oils may contain chemicals other than lipids, including proteins and alkaloids. Lipids can be classified by the way that they are made by an organism, their chemical structure and their limited solubility in water compared to oils, they have a high carbon and hydrogen content and are lacking in oxygen compared to other organic compounds and minerals. Crude oil, or petroleum, its refined components, collectively termed petrochemicals, are crucial resources in the modern economy. Crude oil originates from ancient fossilized organic materials, such as zooplankton and algae, which geochemical processes convert into oil; the name "mineral oil" is a misnomer, in that minerals are not the source of the oil—ancient plants and animals are. Mineral oil is organic. However, it is classified as "mineral oil" instead of as "organic oil" because its organic origin is remote, because it is obtained in the vicinity of rocks, underground traps, sands.
Mineral oil refers to several specific distillates of crude oil. Several edible vegetable and animal oils, fats, are used for various purposes in cooking and food preparation. In particular, many foods are fried in oil much hotter than boiling water. Oils are used for flavoring and for modifying the texture of foods. Cooking oils are derived either from animal fat, as butter and other types, or plant oils from the olive, maize and many other species. Oils are applied to hair to give it a lustrous look, to prevent tangles and roughness and to stabilize the hair to promote growth. See hair conditioner. Oil has been used throughout history as a religious medium, it is considered a spiritually purifying agent and is used for anointing purposes. As a particular example, holy anointing oil has been an important ritual liquid for Judaism and Christianity. Color pigments are suspended in oil, making it suitable as a supporting medium for paints; the oldest known extant oil paintings date from 650 AD. Oils are used for instance in electric transformers.
Heat transfer oils are used both as coolants, for heating and in other applications of heat transfer. Given that they are non-polar, oils do not adhere to other substances; this makes them useful as lubricants for various engineering purposes. Mineral oils are more used as machine lubricants than biological oils are. Whale oil is preferred for lubricating clocks, because it does not evaporate, leaving dust, although its use was banned in the USA in 1980, it is a long-running myth that spermaceti from whales has still been used in NASA projects such as the Hubble Telescope and the Voyager probe because of its low freezing temperature. Spermaceti is not an oil, but a mixture of wax esters, there is no evidence that NASA has used whale oil; some oils burn in liquid or aerosol form, generating light, heat which can be used directly or converted into other forms of energy such as electricity or mechanical work. To obtain many fuel oils, crude oil is pumped from the ground and is shipped via oil tanker or a pipeline to an oil refinery.
There, it is converted from crude oil to diesel fuel, fuel oils, jet fuel, kerosene and liquefied petroleum gas. A 42-US-gallon barrel of crude oil produces 10 US gallons of diesel, 4 US gallons of jet fuel, 19 US gallons of gasoline, 7 US gallons of other products, 3 US gallons split between heavy fuel oil and liquified petroleum gases, 2 US gallons of heating oil; the total production of a barrel of crude into various products results in an increase to 45 US gallons. Not all oils used as fuels are mineral oils, see biodiesel and vegetable oil fuel. In the 18th and 19th cent
In biology and biochemistry, a lipid is a biomolecule, soluble in nonpolar solvents. Non-polar solvents are hydrocarbons used to dissolve other occurring hydrocarbon lipid molecules that do not dissolve in water, including fatty acids, sterols, fat-soluble vitamins, diglycerides and phospholipids; the functions of lipids include storing energy and acting as structural components of cell membranes. Lipids have applications in the food industries as well as in nanotechnology. Scientists sometimes broadly define lipids as amphiphilic small molecules. Biological lipids originate or in part from two distinct types of biochemical subunits or "building-blocks": ketoacyl and isoprene groups. Using this approach, lipids may be divided into eight categories: fatty acids, glycerophospholipids, sphingolipids and polyketides. Although the term "lipid" is sometimes used as a synonym for fats, fats are a subgroup of lipids called triglycerides. Lipids encompass molecules such as fatty acids and their derivatives, as well as other sterol-containing metabolites such as cholesterol.
Although humans and other mammals use various biosynthetic pathways both to break down and to synthesize lipids, some essential lipids can't be made this way and must be obtained from the diet. In 1815, Henry Braconnot classified lipids in two categories and huiles. In 1823, Michel Eugène Chevreul developed a more detailed classification, including oils, tallow, resins and volatile oils. In 1827, William Prout recognized fat, along with protein and carbohydrate, as an important nutrient for humans and animals. For a century, chemists regarded "fats" as only simple lipids made of fatty acids and glycerol, but new forms were described later. Theodore Gobley discovered phospholipids in mammalian brain and hen egg, called by him as "lecithins". Thudichum discovered in human brain some phospholipids and sphingolipids; the terms lipoid, lipin and lipid have been used with varied meanings from author to author. In 1912, Rosenbloom and Gies proposed the substitution of "lipoid" by "lipin". In 1920, Bloor introduced a new classification for "lipoids": simple lipoids, compound lipoids, the derived lipoids.
The word "lipid", which stems etymologically from the Greek lipos, was introduced in 1923 by Gabriel Bertrand. Bertrands included in the concept not only the traditional fats, but the "lipoids", with a complex constitution. In 1947, T. P. Hilditch divided lipids into "simple lipids", with greases and waxes, "complex lipids", with phospholipids and glycolipids. Fatty acids, or fatty acid residues when they are part of a lipid, are a diverse group of molecules synthesized by chain-elongation of an acetyl-CoA primer with malonyl-CoA or methylmalonyl-CoA groups in a process called fatty acid synthesis, they are made of a hydrocarbon chain. The fatty acid structure is one of the most fundamental categories of biological lipids, is used as a building-block of more structurally complex lipids; the carbon chain between four and 24 carbons long, may be saturated or unsaturated, may be attached to functional groups containing oxygen, halogens and sulfur. If a fatty acid contains a double bond, there is the possibility of either a cis or trans geometric isomerism, which affects the molecule's configuration.
Cis-double bonds cause the fatty acid chain to bend, an effect, compounded with more double bonds in the chain. Three double bonds in 18-carbon linolenic acid, the most abundant fatty-acyl chains of plant thylakoid membranes, render these membranes fluid despite environmental low-temperatures, makes linolenic acid give dominating sharp peaks in high resolution 13-C NMR spectra of chloroplasts; this in turn plays an important role in the function of cell membranes. Most occurring fatty acids are of the cis configuration, although the trans form does exist in some natural and hydrogenated fats and oils. Examples of biologically important fatty acids include the eicosanoids, derived from arachidonic acid and eicosapentaenoic acid, that include prostaglandins and thromboxanes. Docosahexaenoic acid is important in biological systems with respect to sight. Other major lipid classes in the fatty acid category are the fatty esters and fatty amides. Fatty esters include important biochemical intermediates such as wax esters, fatty acid thioester coenzyme A derivatives, fatty acid thioester ACP derivatives and fatty acid carnitines.
The fatty amides include N-acyl ethanolamines, such as the cannabinoid neurotransmitter anandamide. Glycerolipids are composed of mono-, di-, tri-substituted glycerols, the best-known being the fatty acid triesters of glycerol, called triglycerides; the word "triacylgl
Tallow is a rendered form of beef or mutton fat, is made up of triglycerides. It is solid at room temperature. Unlike suet, tallow can be stored for extended periods without the need for refrigeration to prevent decomposition, provided it is kept in an airtight container to prevent oxidation. In industry, tallow is not defined as beef or mutton fat. In this context, tallow is animal fat that conforms to certain technical criteria, including its melting point. Commercial tallow contains fat derived from other animals, such as lard from pigs, or from plant sources; the adjacent diagram shows the chemical structure of a typical triglyceride molecule. Greaves is a byproduct of the rendering process, used in making. See the History of dog food. In Leviticus 3:14-17, the Israelites are forbidden to eat the suet surrounding certain internal organs of animals sacrificed at the Temple; this suet is Halakhically called chelev. English Bible translations sometimes translate chelev to "tallow", although the original text only forbids tallow from species offered for sacrifice.
The composition of the fatty acids is as follows: Saturated fatty acids: Palmitic acid: 26% Stearic acid: 14% Myristic acid: 3% Monounsaturated fatty acids: Oleic acid: 47% Palmitoleic acid: 3% Polyunsaturated fatty acids: Linoleic acid: 3% Linolenic acid: 1% Tallow is used in producing soap and animal feed. Some polymer banknotes contain beef tallow. Many items of traditional goods are produced from tallow, available domestically. Tallow can be used as flux for soldering, it is the primary ingredient in some leather conditioners. Tallow used to be used in high-end shaving soaps, in particular those of elite British firms such as Geo. F Trumper, Truefitt & Hill, Taylor of Old Bond Street. While these firms have reformulated to a vegetable base, tallow-based shaving soaps have enjoyed a resurgence in recent years with the gaining popularity of traditional wet-shaving. Makers exist in Turkey and the United States, including artisanal brands Williams and Nod Hill. A significant use of tallow is for the production of shortening and is one of the main ingredients of the Native American food pemmican.
Tallow is traditionally used in deep frying and preferred for this use until the introduction of other oils. Before switching to pure vegetable oil in 1990, the McDonald's corporation cooked its French fries in a mixture of 93% beef tallow and 7% cottonseed oil. According to a 1985 article in the New York Times, tallow was used for frying at Burger King, Wendy's, Hardee's, Arby's, Dairy Queen and Bob's Big Boy. Greaves is a byproduct of the rendering process, used in making, it was both favored and shunned in dog food, but today is found in both wet and dry commercial feeds. Tallow can be used for the production of biodiesel in much the same way as oils from plants are used; because tallow is derived from animal by-products, which have little to no value to commercial food industries, it avoids some of the food vs fuel debate. The United States Air Force has experimented with the use of beef tallow in aviation biofuels. During five days of flight testing from August 23 to 27, 2010, at Edwards Air Force Base, California, a U.
S. Air Force C-17 Globemaster III flew using JP-8 conventional jet fuel in three of its engines and a 50/50 blend of JP-8 and HRJ biofuel made from beef tallow in one engine on August 23, followed by a flight with the same 50/50 blend in all four engines on August 24. On August 27, it flew using a blend of 50% JP-8, 25% HRJ, 25% coal-based fuel made through the Fischer–Tropsch process, becoming the first United States Department of Defense aircraft to fly on such a blend and the first aircraft to operate from Edwards using a fuel derived from beef tallow. Tallow has a use in printmaking, where it is combined with bitumen and applied to metal print plates to provide a resistance to acid etching; the use of trace amounts of tallow as an additive to the substrate used in polymer banknotes came to light in November 2016. Notes issued in 24 countries including Canada and the United Kingdom were found to be affected, leading to objections from vegans and members of some religious communities. Tallow once was used to make molded candles before more convenient wax varieties became available—and for some time after since they continued to be a cheaper alternative.
For those too poor to avail themselves of homemade, molded tallow candles, the "tallow dip"—a strip of burning cloth in a saucer of tallow grease—was an accessible substitute. Early in the development of steam-driven piston engines, the hot vapors and liquids washed away most lubricants quickly, it was soon found. Tallow and compounds including tallow were used to lubricate locomotive and steamship engines at least until the 1950s. Tallow is still used in the steel rolling industry to provide the required lubrication as the sheet steel is compressed through the steel rollers. There is a trend toward replacing tallow-based lubrication with synthetic oils in rolling applications for surface cleanliness reasons; the use of tallow or lard to lubricate rifles was the spark that started the Indian Mutiny of 1857. To load the new Pattern 1853 Enfield Rifle, the sepoys had to bite the cartridge open, it was believed that the pap
Colloquially, room temperature is the range of air temperatures that most people prefer for indoor settings, which feel comfortable when wearing typical indoor clothing. Human comfort can extend beyond this range depending on air circulation and other factors. In certain fields, like science and engineering, within a particular context, room temperature can mean different agreed-on ranges. In contrast, ambient temperature is the actual temperature of the air in any particular place, as measured by a thermometer, it may be different from usual room temperature, for example an unheated room in winter. The American Heritage Dictionary of the English Language identifies room temperature as around 20 to 22 °C, while the Oxford English Dictionary states that it is "conventionally taken as about 20 °C". Owing to variations in humidity and clothing, recommendations for summer and winter may vary; some studies have suggested that thermal comfort preferences of men and women may differ with women on average preferring higher ambient temperatures.
The World Health Organization's standard for comfortable warmth is 18 °C for normal, healthy adults who are appropriately dressed. For those with respiratory problems or allergies, they recommend no less than 16 °C, for the sick, disabled old or young, a minimum of 20 °C. Temperature ranges are defined as room temperature for certain products and processes in industry and consumer goods. For instance, for the shipping and storage of pharmaceuticals, the United States Pharmacopeia-National Formulary defines controlled room temperature as between 20 to 25 °C, with excursions between 15 to 30 °C allowed, provided the mean kinetic temperature does not exceed 25 °C; the European Pharmacopoeia defines it as being 15 to 25 °C, the Japanese Pharmacopeia defines "ordinary temperature" as 15 to 25 °C, with room temperature being 1 to 30 °C. Merriam-Webster gives as a medical definition a range of 15 to 25 °C as being suitable for human occupancy, at which laboratory experiments are performed. People traditionally serve red wine at room temperature.
This practice dates from before central heating, when room temperature in wine-drinking countries was lower than it is today in the range between 15 °C and 18 °C. The advice is therefore to serve the wine at, at most, about 18 °C. Thermal comfort Standard conditions for temperature and pressure ISO 1
Proteins are large biomolecules, or macromolecules, consisting of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, providing structure to cells and organisms, transporting molecules from one location to another. Proteins differ from one another in their sequence of amino acids, dictated by the nucleotide sequence of their genes, which results in protein folding into a specific three-dimensional structure that determines its activity. A linear chain of amino acid residues is called a polypeptide. A protein contains at least one long polypeptide. Short polypeptides, containing less than 20–30 residues, are considered to be proteins and are called peptides, or sometimes oligopeptides; the individual amino acid residues are bonded together by peptide bonds and adjacent amino acid residues. The sequence of amino acid residues in a protein is defined by the sequence of a gene, encoded in the genetic code.
In general, the genetic code specifies 20 standard amino acids. Shortly after or during synthesis, the residues in a protein are chemically modified by post-translational modification, which alters the physical and chemical properties, stability and the function of the proteins. Sometimes proteins have non-peptide groups attached, which can be called prosthetic groups or cofactors. Proteins can work together to achieve a particular function, they associate to form stable protein complexes. Once formed, proteins only exist for a certain period and are degraded and recycled by the cell's machinery through the process of protein turnover. A protein's lifespan covers a wide range, they can exist for years with an average lifespan of 1 -- 2 days in mammalian cells. Abnormal or misfolded proteins are degraded more either due to being targeted for destruction or due to being unstable. Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of organisms and participate in every process within cells.
Many proteins are enzymes that are vital to metabolism. Proteins have structural or mechanical functions, such as actin and myosin in muscle and the proteins in the cytoskeleton, which form a system of scaffolding that maintains cell shape. Other proteins are important in cell signaling, immune responses, cell adhesion, the cell cycle. In animals, proteins are needed in the diet to provide the essential amino acids that cannot be synthesized. Digestion breaks the proteins down for use in the metabolism. Proteins may be purified from other cellular components using a variety of techniques such as ultracentrifugation, precipitation and chromatography. Methods used to study protein structure and function include immunohistochemistry, site-directed mutagenesis, X-ray crystallography, nuclear magnetic resonance and mass spectrometry. Most proteins consist of linear polymers built from series of up to 20 different L-α- amino acids. All proteinogenic amino acids possess common structural features, including an α-carbon to which an amino group, a carboxyl group, a variable side chain are bonded.
Only proline differs from this basic structure as it contains an unusual ring to the N-end amine group, which forces the CO–NH amide moiety into a fixed conformation. The side chains of the standard amino acids, detailed in the list of standard amino acids, have a great variety of chemical structures and properties; the amino acids in a polypeptide chain are linked by peptide bonds. Once linked in the protein chain, an individual amino acid is called a residue, the linked series of carbon and oxygen atoms are known as the main chain or protein backbone; the peptide bond has two resonance forms that contribute some double-bond character and inhibit rotation around its axis, so that the alpha carbons are coplanar. The other two dihedral angles in the peptide bond determine the local shape assumed by the protein backbone; the end with a free amino group is known as the N-terminus or amino terminus, whereas the end of the protein with a free carboxyl group is known as the C-terminus or carboxy terminus.
The words protein and peptide are a little ambiguous and can overlap in meaning. Protein is used to refer to the complete biological molecule in a stable conformation, whereas peptide is reserved for a short amino acid oligomers lacking a stable three-dimensional structure. However, the boundary between the two is not well defined and lies near 20–30 residues. Polypeptide can refer to any single linear chain of amino acids regardless of length, but implies an absence of a defined conformation. Proteins can interact with many types of molecules, including with other proteins, with lipids, with carboyhydrates, with DNA, it has been estimated. Smaller bacteria, such as Mycoplasma or spirochetes contain fewer molecules, on the order of 50,000 to 1 million. By contrast, eukaryotic cells are larger and thus contain much more pro
Essential fatty acid
Essential fatty acids, or EFAs, are fatty acids that humans and other animals must ingest because the body requires them for good health but cannot synthesize them. The term "essential fatty acid" refers to fatty acids required for biological processes but does not include the fats that only act as fuel. Essential fatty acids should not be confused with essential oils, which are "essential" in the sense of being a concentrated essence. Only two fatty acids are known to be essential for humans: linoleic acid; some other fatty acids are sometimes classified as "conditionally essential", meaning that they can become essential under some developmental or disease conditions. When the two EFAs were discovered in 1923, they were designated "vitamin F", but in 1929, research on rats showed that the two EFAs are better classified as fats rather than vitamins; the biological effects of the ω-3 and ω-6 fatty acids are mediated by their mutual interactions, see Essential fatty acid interactions for detail.
In the body, essential fatty acids serve multiple functions. In each of these, the balance between dietary ω-3 and ω-6 affects function, they are modified to make the classic eicosanoids the endocannabinoids the lipoxins which are a group of eicosanoid derivatives formed via the lipoxygenase pathway from ω-6 EFAs and resolvins from ω-3 the isofurans, isoprostanes, epoxyeicosatrienoic acids and Neuroprotectin D They form lipid rafts They act on DNA Fatty acids are straight chain hydrocarbons possessing a carboxyl group at one end. The carbon next to the carboxylate is known as α, the next carbon β, so forth. Since biological fatty acids can be of different lengths, the last position is labelled as a "ω", the last letter in the Greek alphabet; the physiological properties of unsaturated fatty acids depend on the position of the first unsaturation relative to the end position and not the carboxylate. For example, the term ω-3 signifies that the first double bond exists as the third carbon-carbon bond from the terminal CH3 end of the carbon chain.
The number of carbons and the number of double bonds are listed. Ω-3 18:4 or 18:4 ω-3 or 18:4 n−3 indicates an 18-carbon chain with 4 double bonds, with the first double bond in the third position from the CH3 end. Double bonds are separated by a single methylene group unless otherwise noted. In free fatty acid form, the chemical structure of stearidonic acid is: For complete tables of ω-3 and ω-6 essential fatty acids, see Polyunsaturated fatty acids; the essential fatty acids start with the short chain polyunsaturated fatty acids: ω-3 fatty acids: α-Linolenic acid or ALA ω-6 fatty acids: Linoleic acid or LA These two fatty acids cannot be synthesized by humans because humans lack the desaturase enzymes required for their production. They form the starting point for the creation of longer and more desaturated fatty acids, which are referred to as long-chain polyunsaturated fatty acids: ω-3 fatty acids: eicosapentaenoic acid or EPA docosahexaenoic acid or DHA ω-6 fatty acids: gamma-linolenic acid or GLA dihomo-gamma-linolenic acid or DGLA arachidonic acid or AA ω-9 fatty acids are not essential in humans because they can be synthesized from carbohydrates or other fatty acids.
Mammals lack the ability to introduce double bonds in fatty acids beyond carbon 9 and 10, hence ω-6 linoleic acid, abbreviated LA, the ω-3 linolenic acid, abbreviated ALA, are essential for humans in the diet. In humans, arachidonic acid can be synthesized from LA by alternative desaturation and chain elongation. Humans can convert both LA and ALA to docosapentaenoic acid and docosahexaenoic acid although the conversion to DHA is limited, resulting in lower blood levels of DHA than through direct ingestion; this is illustrated by studies in vegetarians. If there is more LA than ALA in the diet it favors the formation of DPA from LA rather than DHA from ALA; this effect can be altered by changing the relative ratio of LA:ALA, but is more effective when total intake of polyunsaturated fatty acids is low. However, the capacity to convert LA to AA and ALA to DHA in the preterm infant is limited, preformed AA and DHA may be required to meet the needs of the developing brain. Both AA and DHA are present in breastmilk and contribute along with the parent fatty acids LA and ALA to meeting the requirements of the newborn infant.
Many infant formulas have AA and DHA added to them with an aim to make them more equivalent to human milk. Essential nutrients are defined as those that cannot be synthesized de novo in sufficient quantities for normal physiological function; this definition is met for ALA but not the longer chain derivatives in adults. The longer chain derivatives however, have pharmacological properties that can modulate disease processes, but this should not be confused with dietary essentiality. Between 1930 and 1950, arachidonic acid and linolenic acid were termed'essential' because each was more or less able to meet the growth requirements of rats given fat-free diets. In the 1950s Arild Hansen showed that in