Conjugated linoleic acids (CLA) are a family of isomers of linoleic acid. In principle, 28 isomers are possible. CLA is found mostly in the meat and dairy products derived from ruminants. The two C=C double bonds are conjugated (i.e., separated by a single bond). CLAs can be either cis-fats or trans-fats.
CLA is marketed as a dietary supplement on the basis of its claimed health benefits. [1]
CLA describes a variety of isomers of octadecadienoic fatty acids. [2]
Commonly, CLAs are studied as some mixture of isomers wherein the isomers c9,t11-CLA (rumenic acid) and t10,c12-CLA were the most abundant. [3] Studies show however that individual isomers have distinct health effects. [4] [5]
Conjugated linoleic acid is both a trans fatty acid and a cis fatty acid. The cis bond causes a lower melting point and, ostensibly, also the observed beneficial health effects. Unlike other trans fatty acids, it may have beneficial effects on human health. [6] CLA is conjugated, and in the United States, trans linkages in a conjugated system are not counted as trans fats for the purposes of nutritional regulations and labeling.[ citation needed ] CLA and some trans isomers of oleic acid are produced by microorganisms in the rumens of ruminants. Non-ruminants, including humans, produce certain isomers of CLA from trans isomers of oleic acid, such as vaccenic acid, which is converted to CLA by delta-9-desaturase. [7] [8]
In healthy humans, CLA and the related conjugated linolenic acid (CLNA) isomers are bioconverted from linoleic acid and alpha-linolenic acid, respectively, mainly by Bifidobacterium bacteria strains inhabiting the gastrointestinal tract.[ citation needed ] However, this bioconversion may not occur at any significant level in those with a digestive disease, gluten sensitivity, or dysbiosis. [9] [10] [11] [12]
CLA is marketed in dietary supplement form for its supposed anti-cancer benefit (for which there is no strong evidence or known mechanism, and very few studies conducted so far) [13] and as a bodybuilding aid. [1] A 2004 review of the evidence said that while CLA seemed to benefit animals, there was a lack of good evidence of human health benefits despite the many claims made for it. [14]
Likewise, there is insufficient evidence that CLA has a useful benefit for overweight or obese people as it has no long-term effect on body composition. [15] Although CLA has shown an effect on insulin response in diabetic rats, there is no evidence of this effect in humans. [16]
Food products from grass-fed ruminants (e.g. mutton and beef) are good sources of CLA and contain much more of it than those from grain-fed animals. [17] Eggs from chickens that have been fed CLA are also rich in CLA, and CLA in egg yolks has been shown to survive the temperatures encountered during frying. [18] Some mushrooms, such as Agaricus bisporus and Agaricus subrufescens , are rare non-animal sources of CLA. [19] [20]
However, dietary punicic acid—which is abundant in pomegranate seeds—is converted to the CLA rumenic acid upon absorption in rats, [21] suggesting that non-animal sources can still effectively provide dietary CLA.
In 1979 CLAs were found to inhibit chemically-induced cancer in mice [22] and research on its biological activity has continued. [23]
In 2008, the United States Food and Drug Administration categorized CLA as generally recognized as safe (GRAS). [24]
In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, from 4 to 28. Fatty acids are a major component of the lipids in some species such as microalgae but in some other organisms are not found in their standalone form, but instead exist as three main classes of esters: triglycerides, phospholipids, and cholesteryl esters. In any of these forms, fatty acids are both important dietary sources of fuel for animals and important structural components for cells.
In nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such compounds, most commonly those that occur in living beings or in food.
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.
α-Linolenic acid, also known as alpha-linolenic acid (ALA), is an n−3, or omega-3, essential fatty acid. ALA is found in many seeds and oils, including flaxseed, walnuts, chia, hemp, and many common vegetable oils.
Oleic acid is a fatty acid that occurs naturally in various animal and vegetable fats and oils. It is an odorless, colorless oil, although commercial samples may be yellowish. In chemical terms, oleic acid is classified as a monounsaturated omega-9 fatty acid, abbreviated with a lipid number of 18:1 cis-9, and a main product of Δ9-desaturase. It has the formula CH3−(CH2)7−CH=CH−(CH2)7−COOH. The name derives from the Latin word oleum, which means oil. It is the most common fatty acid in nature. The salts and esters of oleic acid are called oleates. It is a common component of oils, and thus occurs in many types of food, as well as in soap.
Linoleic acid (LA) is an organic compound with the formula HOOC(CH2)7CH=CHCH2CH=CH(CH2)4CH3. Both alkene groups are cis. It is a fatty acid sometimes denoted 18:2 (n-6) or 18:2 cis-9,12. A linoleate is a salt or ester of this acid.
In biochemistry and nutrition, a polyunsaturated fat is a fat that contains a polyunsaturated fatty acid, which is a subclass of fatty acid characterized by a backbone with two or more carbon–carbon double bonds. Some polyunsaturated fatty acids are essentials. Polyunsaturated fatty acids are precursors to and are derived from polyunsaturated fats, which include drying oils.
Dihomo-γ-linolenic acid (DGLA) is a 20-carbon ω−6 fatty acid. In physiological literature, it is given the name 20:3 (ω−6). DGLA is a carboxylic acid with a 20-carbon chain and three cis double bonds; the first double bond is located at the sixth carbon from the omega end. DGLA is the elongation product of γ-linolenic acid. GLA, in turn, is a desaturation product of linoleic acid. DGLA is made in the body by the elongation of GLA, by an efficient enzyme which does not appear to suffer any form of (dietary) inhibition. DGLA is an extremely uncommon fatty acid, found only in trace amounts in animal products.
Vaccenic acid is a naturally occurring trans fatty acid and an omega-7 fatty acid. It is the predominant kind of trans-fatty acid found in human milk, in the fat of ruminants, and in dairy products such as milk, butter, and yogurt. Trans fat in human milk may depend on trans fat content in food.
Calendic acid is an unsaturated fatty acid, named for the pot marigold, from which it is obtained. It is chemically similar to the conjugated linoleic acids; laboratory work suggests it may have similar in vitro bioactivities.
Rumenic acid, also known as bovinic acid, is a conjugated linoleic acid (CLA) found in the fat of ruminants and in dairy products. It is an omega-7 trans fatty acid. Its lipid shorthand name is cis-9, trans-11 18:2 acid. The name was proposed by Kramer et al. in 1998. It can be considered as the principal dietary form, accounting for as much as 85-90% of the total CLA content in dairy products.
α-Eleostearic acid or (9Z,11E,13E)-octadeca-9,11,13-trienoic acid, is an organic compound, a conjugated fatty acid and one of the isomers of octadecatrienoic acid. It is often called simply eleostearic acid although there is also a β-eleostearic acid. Its high degree of unsaturation gives tung oil its properties as a drying oil.
Conjugated fatty acids is jargon for polyunsaturated fatty acids containing at least one pair of conjugated double bonds. An example of a conjugated fatty acid is the rumenic acid, found in the meat and milk of ruminants. Most unsaturated fatty acids that are doubly unsaturated do not feature conjugation, e.g., linoleic acid and linoelaidic acid.
Punicic acid is a polyunsaturated fatty acid, 18:3 cis-9, trans-11, cis-13. It is named for the pomegranate,, and is obtained from pomegranate seed oil. It has also been found in the seed oils of snake gourd.
Linolelaidic acid is an omega-6 trans fatty acid (TFA) and is a cis–trans isomer of linoleic acid. It is found in partially hydrogenated vegetable oils. It is a white viscous liquid.
Linoleoyl-CoA desaturase (also Delta 6 desaturase, EC 1.14.19.3) is an enzyme that converts between types of fatty acids, which are essential nutrients in the human body. The enzyme mainly catalyzes the chemical reaction
α-Parinaric acid is a conjugated polyunsaturated fatty acid. Discovered by Tsujimoto and Koyanagi in 1933, it contains 18 carbon atoms and 4 conjugated double bonds. The repeating single bond-double bond structure of α-parinaric acid distinguishes it structurally and chemically from the usual "methylene-interrupted" arrangement of polyunsaturated fatty acids that have double-bonds and single bonds separated by a methylene unit (−CH2−). Because of the fluorescent properties conferred by the alternating double bonds, α-parinaric acid is commonly used as a molecular probe in the study of biomembranes.
Trans fat, also called trans-unsaturated fatty acids, or trans fatty acids, is a type of unsaturated fat that occurs in foods. Trace concentrations of trans fats occur naturally, but large amounts are found in some processed foods. Since consumption of trans fats is unhealthy, artificial trans fats are highly regulated or banned in many nations. However, they are still widely consumed in developing nations, resulting in hundreds of thousands of deaths each year. The World Health Organization (WHO) had set a goal to make the world free from industrially produced trans fat by the end of 2023.
{{cite journal}}: Cite journal requires |journal= (help)CS1 maint: location (link)On July 24, the U.S. Food and Drug Administration announced its finding that conjugated linoleic acid, known as CLA, is "generally regarded as safe" for use in foods