Essential fatty acids function

Essential fatty acids function

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Why are essential fatty acids so essential? I know that if taken less then it would cause diseases, but what metabolic role do they play? Are their importance is just because of their structural role?

Essential fatty acids consist of two main EFAs - Omega 3 (Linoleic acid) and Omega 6 (Linolenic acid).

These two play vital roles in the following:

  • Growth and development
  • Brain functioning
  • Skin health
  • Hair growth
  • Metabolism
  • Reproductive system health
  • Cell membrane integrity.

The fact that are bodies can't make them makes them very important in our diet. They are most important in our cell membranes.

Omega 3 is an amazing anti-flammatory. It does this by blocking the inflammation pathways in the cell.

We need more Omega 3 than 6 - about a ratio of 2:1.

This is a pretty good page if you want more information.

Nonessential and Essential Fatty Acids

Fatty acids are vital for the normal operation of all body systems. The circulatory system, respiratory system, integumentary system, immune system, brain, and other organs require fatty acids for proper function. The body is capable of synthesizing most of the fatty acids it needs from food. These fatty acids are known as nonessential fatty acids. However, there are some fatty acids that the body cannot synthesize and these are called essential fatty acids. It is important to note that nonessential fatty acids doesn&rsquot mean unimportant the classification is based solely on the ability of the body to synthesize the fatty acid.

Essential fatty acids must be obtained from food. They fall into two categories&mdashomega-3 and omega-6. The 3 and 6 refer to the position of the first carbon double bond and the omega refers to the methyl end of the chain. Omega-3 and omega-6 fatty acids are precursors to important compounds called eicosanoids. Eicosanoids are powerful hormones that control many other hormones and important body functions, such as the central nervous system and the immune system. Eicosanoids derived from omega-6 fatty acids are known to increase blood pressure, immune response, and inflammation. In contrast, eicosanoids derived from omega-3 fatty acids are known to have heart-healthy effects. Given the contrasting effects of the omega-3 and omega-6 fatty acids, a proper dietary balance between the two must be achieved to ensure optimal health benefits.

Essential fatty acids play an important role in the life and death of cardiac cells, immune system function, and blood pressure regulation. Docosahexaenoic acid (DHA) is an omega-3 essential fatty acid shown to play important roles in synaptic transmission in the brain during fetal development.

Some excellent sources of omega-3 and omega-6 essential fatty acids are fish, flaxseed oil, hemp, walnuts, and leafy vegetables. Because these essential fatty acids are easily accessible, essential fatty acid deficiency is extremely rare.

Figure 5.6 Essential Fatty Acids

Image by Allison Calabrese / CC BY 4.0

7 Things To Know About Omega-3 Fatty Acids

Omega-3 fatty acids are a group of polyunsaturated fatty acids that are important for a number of functions in the body. The omega-3 fatty acids EPA and DHA are found in seafood, such as fatty fish (e.g., salmon, tuna, and trout) and shellfish (e.g., crab, mussels, and oysters). A different kind of omega-3, called ALA, is found in other foods, including some vegetable oils (e.g., canola and soy). Omega-3s are also available as dietary supplements for example, fish oil supplements contain EPA and DHA, and flaxseed oil supplements contain ALA. Moderate evidence has emerged about the health benefits of consuming seafood. The health benefits of omega-3 dietary supplements are unclear.

Here are 7 things you should know about omega-3s:

Results of studies on diets rich in seafood (fish and shellfish) and heart disease provide moderate evidence that people who eat seafood at least once a week are less likely to die of heart disease than those who rarely or never eat seafood. The Dietary Guidelines for Americans, 2010 (3MB PDF) includes a new recommendation that adults eat 8 or more ounces of a variety of seafood per week because it provides a range of nutrients, including omega-3 fatty acids. (Smaller amounts are recommended for young children, and there are special recommendations for pregnant or breastfeeding women. See Tip #4.)

Evidence suggests that seafood rich in EPA and DHA should be included in a heart-healthy diet however, supplements of EPA and DHA have not been shown to protect against heart disease. In 2012, two groups of scientists analyzed the research on the effects of EPA/DHA supplements on heart disease risk. One group analyzed only studies in people with a history of heart disease, and the other group analyzed studies in people both with and without a history of heart disease. Neither review found strong evidence of a protective effect of the supplements.

A 2012 review of the scientific literature concluded that EPA and DHA, the types of omega-3s found in seafood and fish oil, may be modestly helpful in relieving symptoms of rheumatoid arthritis. In the studies included in the review, many of the participants reported that when they were taking fish oil they had briefer morning stiffness, less joint swelling and pain, and less need for anti-inflammatory drugs to control their symptoms.

The nutritional value of seafood is of particular importance during fetal growth and development, as well as in early infancy and childhood. Women who are pregnant or breastfeed should consume 8 to 12 ounces of seafood per week from a variety of seafood types that are low in methyl mercury as part of a healthy eating pattern and while staying within their calorie needs. Pregnant or breastfeeding women should limit the amount of white tuna (labeled as “albacore”) to no more than 6 ounces per week. They should not eat tilefish, shark, swordfish, and king mackerel because they are high in methyl mercury.

There is ongoing research on omega-3 fatty acids and diseases of the brain and eye, but there is not enough evidence to draw conclusions about the effectiveness of omega-3s for these conditions. DHA plays important roles in the functioning of the brain and the eye. Researchers are actively investigating the possible benefits of DHA and other omega-3 fatty acids in preventing or treating a variety of brain- and eye-related conditions.

There is conflicting evidence about whether a link might exist between the omega-3 fatty acids found in seafood and fish oil (EPA/DHA) and an increased risk of prostate cancer. Additional research on the association of omega-3 consumption and prostate cancer risk is under way.

The bottom line: Including seafood in your diet is healthful. Whether omega-3 supplements are beneficial is uncertain. If you are considering omega-3 supplements, talk to your health care provider. It’s especially important to consult your (or your child’s) health care provider if you are pregnant or breastfeeding, if you take medicine that affects blood clotting, if you are allergic to seafood, or if you are considering giving a child an omega-3 supplement.

Fatty Acids: Subject-Matter and Functions | Microbiology

Let us learn about Fatty Acids. After reading this article you will learn about: 1. Subject-Matter of Fatty Acids 2. Function or Uses of Lipids.

Subject-Matter of Fatty Acids:

Fatty acids are compounds consisting of a long hydrocarbon chain with a carboxylate group at one end. The general formula is CH3 (CH2)n COOH.

They are obtained from the lipids of most plants and animals and have the following characteristics:

(i) They are usually monocarboxylic acids, R-CO2H.

(ii) They possess an even number of carbon atoms.

(iii) The R group is usually an un-branched chain.

(iv) The R group may be saturated, or it may have 1, 2, or 3 double bonds.

Fatty acids are divided into 2 classes depending upon whether or not the carbon chain carries the maximum possible number of attached hydrogen’s.

If all carbon atoms are fully saturated h with hydrogen, the fatty acid is called saturated and has the structure like:

The most abundant saturated fatty acids are palmitic acid, CH3(CH2)14 COOH, and stearic acid, CH3(CH2)16 COOH. These and some other acids along with glycerol form the bulk of the body fat in most organisms.

When all the carbon atoms are not fully saturated with hydrogen, they are joined by double bonds and the fatty acid is called unsaturated:

Typical unsaturated fatty acids are oleic acid, CH3(CH2)7 CH = CH (CH2)7 COOH or C17H33COOH and linoleic acid CH3(CH2)4CH = CHCH2CH = CH(CH2)7COOH. Linoleic acid has more than one carbon-carbon double bond and is thus polyunsaturated.

Their chemical structure is as follows:

The melting point of a fatty acid depends on its nature or kind, the greater the degree of unsaturation, the lower the melting point. For example, the melting point of the stearic acid (saturated) is 70° C and that of oleic acid (one double bond) and linoleic acid (2 double bonds) is 4°C and -5°C respectively. For this reason, most animal fats are solids and most vegetable oils are liquids at room temperature.

The oils are more unsaturated than the fats because they are composed of the glycerides of unsaturated fatty acids. The hydrogenation of the double bonds of the fatty acid present in oils (converting them into saturated acids) raises the melting point of the glycerides.

The “hardening” of vegetable oil such as the cotton seed or groundnut oil is an important commercial process by which the cooking fats like “Dalda”, etc., are produced.

Function or Uses of Lipids:

Fats and fatty acids are important food storage compounds in most organisms. The fat is stored in the adipose tissue. Like carbohydrates and proteins, fats also play significant role as structural component of cells. For example, certain phospholipids form an important component of the cell membranes and of enzyme systems in the mitochondria.

Phosphatides have also been considered essential for the formation of one of the blood clotting factors. Phospholipid cephalin helps in the formation of prothrombinase which converts prothrombin into thrombin during blood coagulation. Some complex lipids are also found in the brain and nerve tissue and in the heart and skeletal muscles. Besides, the oxidation of fats provides a large amount of energy to body cells.

The animal fats are the most important source of some of the vitamins, i.e., A and D. The steroids are also of great physiological importance and the cholesterol is the main precursor of steroid hormones, (e.g., estrogen progesterone, corticosterone) which affect cellular activities by influencing gene expression. Some steroids are vitamins (e.g., vitamin D2) and influence the activities of certain cellular enzymes.

Other steroids are regular constituents of membranes, where they influence membrane structure, permeability and transport.

A little extra: Lipids and Health

Polyunsaturated Fatty Acids (PUFAs) are characterized by long hydrocarbon chains, studded with double bonds and having a carboxylic acid group at one end. There are two subclasses under the PUFA umbrella: omega-3 and omega-6 fatty acids. The main distinction lies in the name &ldquo3&rdquo and &ldquo6&rdquo denote the positions of the first double bond in the molecule, starting from the CH3 end. They are both Essential Fatty Acids (EFAs) which are are abundant and essential to the human brain and eyes, as well as in deep sea marine flora and microbes that are exposed to high pressure and low temperature conditions.

Essential fatty acids are useful for signal-transduction cascades as substrates that bind to receptors that initiate downstream cellular signals to induce the desired effect. For example, omega-3 fatty acids have been known to act as anti-inflammatory agents, but the mechanism of action was largely unexplained. New advances have proposed one pathway showing that when omega-3 fatty acids bind to GPR120, a G-protein coupled receptor, the receptor can activate subsequent pathways leading to anti-inflammatory signaling within tissues. (To read more, read the paper here).

DHA (docosahexaenoic acid) is important for visual development and retinal function. Humans cannot synthesize DHA, so it must be included in our diets. The highest DHA concentration in the human body is in the retina, the delicate membrane in the back of the eye that holds photoreceptors (rods and cones) and nerve endings. Low levels of this fatty acid in the retina has been associated with age-related macular degeneration and diabetic retinopathy.

Structure of docosahexaenoic acid (DHA)

One of DHA&rsquos many roles in the retina is promoting photoreceptor survival and development. In rats raised on a DHA-deficient diet, photoreceptor cell cultures began to initiate apoptosis after 7-12 days, but the addition of DHA at day 7 was able to rescue the photoreceptor cells and prevented their death (Rotstein et al.). This allows time for the photoreceptors to develop and undergo apical membrane differentiation, which elongates the cell.

In neuronal tissue, DHA is involved in neurotransmitter carrier-mediated transport between synapses. One example takes place where the axon terminal converges onto the target cell. Since most neurotransmitters leave the neuron encased in vesicles, they must first travel, bind, and fuse to the correct target membrane. This specificity is mediated through proteins called SNAREs the incoming vesicle has v-SNAREs, and the target membrane holds t-SNAREs, which entwine upon vesicle docking. DHA has been found to facilitate formation of this SNARE complex, which facilitates the fusion of neurotransmitter-carrying synaptic vesicles to the target cell. In this way, DHA plays an essential role in neuronal signaling. Read a review of DHA functions here.

&ldquoOffice of Dietary Supplements - Omega-3 Fatty Acids.&rdquo NIH Office of Dietary Supplements, U.S. Department of Health and Human Services, 21 Nov. 2018,

GPR120 Oh et al. Oh, Da Young, et al. "GPR120 is an omega-3 fatty acid receptor mediating potent anti-inflammatory and insulin-sensitizing effects." Cell 142.5 (2010): 687-698.

Photoreceptor survival: Rotstein, Nora P., et al. "Docosahexaenoic acid is required for the survival of rat retinal photoreceptors in vitro." Journal of neurochemistry 66.5 (1996): 1851-1859.

DHA function review : Tanaka, Kazuhiro, et al. "Effects of docosahexaenoic acid on neurotransmission." Biomolecules & therapeutics 20.2 (2012): 152.

Essential fatty acids function - Biology

Figure 1. A healthy diet should include a variety of foods to ensure that needs for essential nutrients are met. (credit: Keith Weller, USDA ARS)

While the animal body can synthesize many of the molecules required for function from the organic precursors, there are some nutrients that need to be consumed from food. These nutrients are termed essential nutrients, meaning they must be eaten, and the body cannot produce them.

The omega-3 alpha-linolenic acid and the omega-6 linoleic acid are essential fatty acids needed to make some membrane phospholipids. Vitamins are another class of essential organic molecules that are required in small quantities for many enzymes to function and, for this reason, are considered to be co-enzymes. Absence or low levels of vitamins can have a dramatic effect on health, as outlined in Table 1 and Table 2. Both fat-soluble and water-soluble vitamins must be obtained from food.

Table 1. Water-soluble Essential Vitamins
Vitamin Function Deficiencies Can Lead To Sources
Vitamin B1 (Thiamine) Needed by the body to process lipids, proteins, and carbohydrates Coenzyme removes CO2 from organic compounds Muscle weakness, Beriberi: reduced heart function, CNS problems Milk, meat, dried beans, whole grains
Vitamin B2 (Riboflavin) Takes an active role in metabolism, aiding in the conversion of food to energy (FAD and FMN) Cracks or sores on the outer surface of the lips (cheliosis) inflammation and redness of the tongue moist, scaly skin inflammation (seborrheic dermatitis) Meat, eggs, enriched grains, vegetables
Vitamin B3 (Niacin) Used by the body to release energy from carbohydrates and to process alcohol required for the synthesis of sex hormones component of coenzyme NAD + and NADP + Pellagra, which can result in dermatitis, diarrhea, dementia, and death Meat, eggs, grains, nuts, potatoes
Vitamin B5 (Pantothenic acid) Assists in producing energy from foods (lipids, in particular) component of coenzyme A Fatigue, poor coordination, retarded growth, numbness, tingling of hands and feet Meat, whole grains, milk, fruits, vegetables
Vitamin B6 (Pyridoxine) The principal vitamin for processing amino acids and lipids also helps convert nutrients into energy Irritability, depression, confusion, mouth sores or ulcers, anemia, muscular twitching Meat, dairy products, whole grains, orange juice
Vitamin B7 (Biotin) Used in energy and amino acid metabolism, fat synthesis, and fat breakdown helps the body use blood sugar Hair loss, dermatitis, depression, numbness and tingling in the extremities neuromuscular disorders Meat, eggs, legumes and other vegetables
Vitamin B9 (Folic acid) Assists the normal development of cells, especially during fetal development helps metabolize nucleic and amino acids Deficiency during pregnancy is associated with birth defects, such as neural tube defects and anemia Leafy green vegetables, whole wheat, fruits, nuts, legumes
Vitamin B12 (Cobalamin) Maintains healthy nervous system and assists with blood cell formation coenzyme in nucleic acid metabolism Anemia, neurological disorders, numbness, loss of balance Meat, eggs, animal products
Vitamin C (Ascorbic acid) Helps maintain connective tissue: bone, cartilage, and dentin boosts the immune system Scurvy, which results in bleeding, hair and tooth loss joint pain and swelling delayed wound healing Citrus fruits, broccoli, tomatoes, red sweet bell peppers
Table 2. Fat-soluble Essential Vitamins
Vitamin Function Deficiencies Can Lead To Sources
Vitamin A (Retinol) Critical to the development of bones, teeth, and skin helps maintain eyesight, enhances the immune system, fetal development, gene expression Night-blindness, skin disorders, impaired immunity Dark green leafy vegetables, yellow-orange vegetables fruits, milk, butter
Vitamin D Critical for calcium absorption for bone development and strength maintains a stable nervous system maintains a normal and strong heartbeat helps in blood clotting Rickets, osteomalacia, immunity Cod liver oil, milk, egg yolk
Vitamin E (Tocopherol) Lessens oxidative damage of cells,and prevents lung damage from pollutants vital to the immune system Deficiency is rare anemia, nervous system degeneration Wheat germ oil, unrefined vegetable oils, nuts, seeds, grains
Vitamin K (Phylloquinone) Essential to blood clotting Bleeding and easy bruising Leafy green vegetables, tea

Minerals, listed in Table 3, are inorganic essential nutrients that must be obtained from food. Among their many functions, minerals help in structure and regulation and are considered co-factors.

Table 3. Minerals and Their Function in the Human Body
Vitamin Function Deficiencies Can Lead To Sources
Calcium* Needed for muscle and neuron function heart health builds bone and supports synthesis and function of blood cells nerve function Osteoporosis, rickets, muscle spasms, impaired growth Milk, yogurt, fish, green leafy vegetables, legumes
Chlorine* Needed for production of hydrochloric acid (HCl) in the stomach and nerve function osmotic balance Muscle cramps, mood disturbances, reduced appetite Table salt
Copper (trace amounts) Required component of many redox enzymes, including cytochrome c oxidase cofactor for hemoglobin synthesis Copper deficiency is rare Liver, oysters, cocoa, chocolate, sesame, nuts
Iodine Required for the synthesis of thyroid hormones Goiter Seafood, iodized salt, dairy products
Iron Required for many proteins and enzymes, notably hemoglobin, to prevent anemia Anemia, which causes poor concentration, fatigue, and poor immune function Red meat, leafy green vegetables, fish (tuna, salmon), eggs, dried fruits, beans, whole grains
Magnesium* Required co-factor for ATP formation bone formation normal membrane functions muscle function Mood disturbances, muscle spasms Whole grains, leafy green vegetables
Manganese (trace amounts) A cofactor in enzyme functions trace amounts are required Manganese deficiency is rare Common in most foods
Molybdenum (trace amounts) Acts as a cofactor for three essential enzymes in humans: sulfite oxidase, xanthine oxidase, and aldehyde oxidase Molybdenum deficiency is rare
Phosphorus* A component of bones and teeth helps regulate acid-base balance nucleotide synthesis Weakness, bone abnormalities, calcium loss Milk, hard cheese, whole grains, meats
Potassium* Vital for muscles, heart, and nerve function Cardiac rhythm disturbance, muscle weakness Legumes, potato skin, tomatoes, bananas
Selenium (trace amounts) A cofactor essential to activity of antioxidant enzymes like glutathione peroxidase trace amounts are required Selenium deficiency is rare Common in most foods
Sodium* Systemic electrolyte required for many functions acid-base balance water balance nerve function Muscle cramps, fatigue, reduced appetite Table salt
Zinc (trace amounts) Required for several enzymes such as carboxypeptidase, liver alcohol dehydrogenase, and carbonic anhydrase Anemia, poor wound healing, can lead to short stature Common in most foods
*Greater than 200mg/day required

Certain amino acids also must be procured from food and cannot be synthesized by the body. These amino acids are the “essential” amino acids. The human body can synthesize only 11 of the 20 required amino acids the rest must be obtained from food. The essential amino acids are listed in Table 4.

Fats and Oils

A fat molecule, such as a triglyceride, consists of two main components—glycerol and fatty acids. Glycerol is an organic compound with three carbon atoms, five hydrogen atoms, and three hydroxyl (–OH) groups. Fatty acids have a long chain of hydrocarbons to which an acidic carboxyl group is attached, hence the name “fatty acid.” The number of carbons in the fatty acid may range from 4 to 36 most common are those containing 12–18 carbons. In a fat molecule, a fatty acid is attached to each of the three oxygen atoms in the –OH groups of the glycerol molecule with a covalent bond (Figure 2).

Figure 2. Lipids include fats, such as triglycerides, which are made up of fatty acids and glycerol, phospholipids, and steroids.

During this covalent bond formation, three water molecules are released. The three fatty acids in the fat may be similar or dissimilar. These fats are also called triglycerides because they have three fatty acids. Some fatty acids have common names that specify their origin. For example, palmitic acid, a saturated fatty acid, is derived from the palm tree. Arachidic acid is derived from Arachis hypogaea, the scientific name for peanuts.

Fatty acids may be saturated or unsaturated. In a fatty acid chain, if there are only single bonds between neighboring carbons in the hydrocarbon chain, the fatty acid is saturated. Saturated fatty acids are saturated with hydrogen in other words, the number of hydrogen atoms attached to the carbon skeleton is maximized.

When the hydrocarbon chain contains a double bond, the fatty acid is an unsaturated fatty acid.

Most unsaturated fats are liquid at room temperature and are called oils. If there is one double bond in the molecule, then it is known as a monounsaturated fat (e.g., olive oil), and if there is more than one double bond, then it is known as a polyunsaturated fat (e.g., canola oil).

Saturated fats tend to get packed tightly and are solid at room temperature. Animal fats with stearic acid and palmitic acid contained in meat, and the fat with butyric acid contained in butter, are examples of saturated fats. Mammals store fats in specialized cells called adipocytes, where globules of fat occupy most of the cell. In plants, fat or oil is stored in seeds and is used as a source of energy during embryonic development.

Unsaturated fats or oils are usually of plant origin and contain unsaturated fatty acids. The double bond causes a bend or a “kink” that prevents the fatty acids from packing tightly, keeping them liquid at room temperature. Olive oil, corn oil, canola oil, and cod liver oil are examples of unsaturated fats. Unsaturated fats help to improve blood cholesterol levels, whereas saturated fats contribute to plaque formation in the arteries, which increases the risk of a heart attack.

Margarine, some types of peanut butter, and shortening are examples of artificially hydrogenated trans-fats. Recent studies have shown that an increase in trans-fats in the human diet may lead to an increase in levels of low-density lipoprotein (LDL), or “bad” cholesterol, which, in turn, may lead to plaque deposition in the arteries, resulting in heart disease. Many fast food restaurants have recently eliminated the use of trans-fats, and U.S. food labels are now required to list their trans-fat content.In the food industry, oils are artificially hydrogenated to make them semi-solid, leading to less spoilage and increased shelf life. Simply speaking, hydrogen gas is bubbled through oils to solidify them. During this hydrogenation process, double bonds of the cis-conformation in the hydrocarbon chain may be converted to double bonds in the trans-conformation. This forms a trans-fat from a cis-fat. The orientation of the double bonds affects the chemical properties of the fat (Figure 3).

Figure 3. During the hydrogenation process, the orientation around the double bonds is changed, making a trans-fat from a cis-fat. This changes the chemical properties of the molecule.

Essential fatty acids are fatty acids that are required but not synthesized by the human body. Consequently, they must be supplemented through the diet. Omega-3 fatty acids fall into this category and are one of only two known essential fatty acids for humans (the other being omega-6 fatty acids). They are a type of polyunsaturated fat and are called omega-3 fatty acids because the third carbon from the end of the fatty acid participates in a double bond.

Salmon, trout, and tuna are good sources of omega-3 fatty acids. Omega-3 fatty acids are important in brain function and normal growth and development. They may also prevent heart disease and reduce the risk of cancer.

Like carbohydrates, fats have received a lot of bad publicity. It is true that eating an excess of fried foods and other “fatty” foods leads to weight gain. However, fats do have important functions. Fats serve as long-term energy storage. They also provide insulation for the body. Therefore, “healthy” unsaturated fats in moderate amounts should be consumed on a regular basis.

Nucleic Acids

Nucleic acids are key macromolecules in the continuity of life. They carry the genetic blueprint of a cell and carry instructions for the functioning of the cell.

The two main types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA is the genetic material found in all living organisms, ranging from single-celled bacteria to multicellular mammals.

The other type of nucleic acid, RNA, is mostly involved in protein synthesis. The DNA molecules never leave the nucleus, but instead use an RNA intermediary to communicate with the rest of the cell. Other types of RNA are also involved in protein synthesis and its regulation.

DNA and RNA are made up of monomers known as nucleotides. The nucleotides combine with each other to form a polynucleotide, DNA or RNA. Each nucleotide is made up of three components: a nitrogenous base, a pentose (five-carbon) sugar, and a phosphate group (Figure 2.3.10). Each nitrogenous base in a nucleotide is attached to a sugar molecule, which is attached to a phosphate group.

Figure 2.3.10: A nucleotide is made up of three components: a nitrogenous base, a pentose sugar, and a phosphate group.

Nomenclature and terminology Edit

Fatty acids are straight chain hydrocarbons possessing a carboxyl group (–COOH) group at one end, and a methyl group (–CH3) at the other end. The carbon next to the carboxylate is known as α, the next carbon β, and 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 largely depend on the position of the first unsaturation relative to the end position (ω). For example, the term ω-3 signifies that the first unsaturated carbon-carbon bond from the terminal end (ω) of then chain is the third one. Typically, the number of carbons and the number of double bonds are also listed in short descriptions of unsaturated fatty acids.

For instance, ω-3 18:4, or 18:4 ω-3, or 18:4 n−3 indicates stearidonic acid, an 18-carbon chain with 4 double bonds, and with a double bond between the third and fourth carbon atoms from the CH3 end. Double bonds are cis and separated by a single methylene (CH2) group unless otherwise noted. In free fatty acid form, the chemical structure of stearidonic acid is:

Examples Edit

Polyunsaturated fatty acids with 16-carbon and 18-carbon chains are sometimes classified as short chain polyunsaturated fatty acids (SC-PUFA), as opposed to long-chain polyunsaturated fatty acids (LC-PUFA), which have more than 18 carbon atoms. [6]

Both the essential fatty acids are SC-PUFA with an 18-carbon chain:

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 more desaturated fatty acids, most of which also have a longer carbon chain:

Except for GLA, which has a short 18-carbon chain, these fatty acids have more than 18 carbon atoms and are typically classified as LC-PUFA. [6]

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 the omega-6 linoleic acid (18:2n-6 LA) and the omega-3 linolenic acid (18:3n-3 ALA) are essential for humans in the diet. However, humans can convert both LA and ALA to fatty acids with longer carbon chains and a larger number of double bonds, by alternative desaturation and chain elongation.

In humans, arachidonic acid (20:4n-6 AA) can be synthesized from LA. In turn, AA can be converted to an even longer fatty acid, the docosapentaenoic acid (22:5n-6 DPA). Similarly, ALA can be converted to docosahexaenoic acid (22:6n-3 DHA), although the latter conversion is limited, resulting in lower blood levels of DHA than through direct ingestion. This is illustrated by studies in vegans and vegetarians. [7] If there is relatively 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.

In preterm infants, the capacity to convert LA to AA and ALA to DHA is limited, and 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 LA and ALA but not the longer chain derivatives in adults. [8] The longer chain derivatives particularly, 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 humans: infants fed skimmed milk developed the essential fatty acid deficiency. It was characterized by an increased food intake, poor growth, and a scaly dermatitis, and was cured by the administration of corn oil.

Later work by Hansen randomized 426 children to four treatments: modified cow's milk formula, skimmed milk formula, skimmed milk formula with coconut oil, or cow's milk formula with corn oil. The infants who received the skimmed milk formula or the formula with coconut oil developed essential fatty acid deficiency signs and symptoms. This could be cured by administration of ethyl linoleate (the ethyl ester of linoleic acid) with about 1% of the energy intake. [9]

Collins et al. 1970 [10] were the first to demonstrate linoleic acid deficiency in adults. They found that patients undergoing intravenous nutrition with glucose became isolated from their fat supplies and rapidly developed biochemical signs of essential fatty acid deficiency (an increase in 20:3n-9/20:4n-6 ratio in plasma) and skin symptoms. This could be treated by infusing lipids, and later studies showed that topical application of sunflower oil would also resolve the dermal symptoms. [11] Linoleic acid has a specific role in maintaining the skin water-permeability barrier, probably as constituents of acylglycosylceramides. This role cannot be met by any ω-3 fatty acids or by arachidonic acid.

The main physiological requirement for ω-6 fatty acids is attributed to arachidonic acid. Arachidonic acid is the major precursor of prostaglandins, leukotrienes that play a vital role in cell signaling, and an endogenous cannabinoid anandamide. [12] Metabolites from the ω-3 pathway, mainly from eicosapentaenoic acid, are mostly inactive, and this explains why ω-3 fatty acids do not correct the reproductive failure in rats where arachidonic is needed to make active prostaglandins that cause uterine contraction. [13] To some extent, any ω-3 or ω-6 can contribute to the growth-promoting effects of EFA deficiency, but only ω-6 fatty acids can restore reproductive performance and correct the dermatitis in rats. Particular fatty acids are still needed at critical life stages (e.g. lactation) and in some disease states.

In nonscientific writing, common usage is that the term essential fatty acid comprises all the ω-3 or -6 fatty acids. Conjugated fatty acids like calendic acid are not considered essential. Authoritative sources include the whole families, but generally only make dietary recommendations for LA and ALA with the exception of DHA for infants under the age of 6 months. Recent reviews by WHO/FAO in 2009 and the European Food Safety Authority [14] have reviewed the evidence and made recommendations for minimal intakes of LA and ALA and have also recommended intakes of longer chain ω-3 fatty acids based on the association of oily fish consumption with a lower risk of cardiovascular disease. Some earlier review lumped all polyunsaturated fatty acids together without qualification whether they were short or long-chain PUFA or whether they were ω-3 and ω-6 PUFA. [15] [16] [17]

Conditional essentiality Edit

Traditionally speaking, the LC-PUFAs are not essential to healthy adults. Because the LC-PUFA are sometimes required, they may be considered conditionally essential fatty acids. [18]

Essential fatty acids play a part in many metabolic processes, and there is evidence to suggest that low levels of essential fatty acids, or the wrong balance of types among the essential fatty acids, may be a factor in a number of illnesses, including osteoporosis. [19]

Fish is the main source of the longer omega-3 fats eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), though they initially acquire these fats through the consumption of algae and seaweed. Some plant-based foods contain omega-3 in the form of alpha-linolenic acid (ALA), which appears to have a modest benefit for cardiovascular health. [20] The human body can (and in case of a purely vegetarian diet often must unless certain algae or supplements derived from them are consumed) convert ALA to EPA and subsequently DHA. This elongation of ALA is inefficient. Conversion to DHA is higher in women than in men this is thought to reflect the need to provide DHA to the fetus and infant during pregnancy and breast feeding. [21]

The IUPAC Lipid Handbook provides a very large and detailed listing of fat contents of animal and vegetable fats, including ω-3 and -6 oils. [22] The National Institutes of Health's EFA Education group publishes Essential Fats in Food Oils. [23] This lists 40 common oils, more tightly focused on EFAs and sorted by n-6:3 ratio. Vegetable Lipids as Components of Functional Food lists notable vegetable sources of EFAs as well as commentary and an overview of the biosynthetic pathways involved. [24] Careful readers will note that these sources are not in excellent agreement. EFA content of vegetable sources varies with cultivation conditions. Animal sources vary widely, both with the animal's feed and that the EFA makeup varies markedly with fats from different body parts.

Types of Fatty Acids

Fatty acids are monocarboxylic acids that are found in natural fats or lipids. As they are prepared from fats, they are so named. A fatty acid is one of the major components of a triglyceride, which is a form of lipid that is used in the body to stock up energy. A lipid is just a type of molecule that includes, among other things, fatty acids. Triglycerides are a secondary energy source that the body can use in the event that there is not enough sugarin the system. While fatty acids vary in terms of chemical individuality, they all have some basic qualities in common.

Types of fatty acids

According to their structure fatty acids are classified into four classes—
1) simple or straight chain fatty acids,
2) branched chain fatty acids,
3) hydroxyl fatty acids and
4) Cyclic fatty acids.

Simple or straight chain types of fatty acids

Most of the common fatty acids belong to this group in which the carbon atoms remain arranged in a single straight chain. These may be divided into two subclasses—(a) saturated and (b) unsaturated.

Saturated types of fatty acids

There is no double bond in the carbon chain of these types of fatty acids. They have the general formula CnH2nO2 or CnH2n+i COOH or CH3 (CH2)n COOH and they occur in two series- even carbon fatty acids and odd carbon fatty acids that contain even and odd number of C atoms in their molecules respectively. The former series (even carbon acids) are more plentiful in nature, ranging from C2 to C26. Among these the most common is CK, fatty acid called palmitic acid. Other common examples of even carbon fatty acids are acetic acid (C2), butyric acid (C4), stearic acid (C6) etc. Odd carbon fatty acids ranging between Ca to C25 are also found in nature, but much less frequently. A few examples of odd carbon fatty acids are propionic acid (Cs), valeric acid (Cs), heptanoic acid (Cy) etc.

Unsaturated types of fatty acids

This group is characterized by having one or more double bond(s) in their carbon chain. According to the number of double bonds present in the molecule, such types of fatty acids are grouped as monoenoic, dienoic, trienoic, tetraenoic, pentaenoic etc. However, those containing more than one of double bonds are collectively referred to as polyenoic acids. Common examples of such fatty acids are oleic acid, palmitioleic acid, linolenic acid, linoleic acid, arachidonic acid etc. Three of these namely linolenic acid, linoleic acid and arachidonic acids are called essential fatty acids because they are not synthesized in our body but are essentially required for growth and hence they must be taken through diet.

Branched chain types of fatty acids

Some even or odd carbon fatty acids have branched chains. These are less abundant in nature. The more common saturated methyl-branched fatty acids can often be identified from the mass spectra of their methyl ester derivatives, especially when spectra of model compounds are available for comparison purposes. Example of such types of fatty acids are obutyric acid, isovaleric acid etc.

Hydroxyl types of fatty acids

In some saturated or unsaturated fatty acids, one or more H atoms are substituted by hydroxyl (-OH) groups. Example of these types of fatty acids is cerebronic acid, ricinoleic acid, dihydroxystearic acid etc.

Cyclic types of fatty acids

Fatty acids containing hydrocarbon ring are of this type. Example of these types of fatty acids are, chaulmoogric acid, gorlic acid etc. Fatty acids containing up to ten carbon atoms are referred to as lower (or small chain) fatty acids where as those having more than ten carbon atoms are called higher or long chain fatty acids.

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