Pregnancy potentially lower birth weight in newborns. Please note that CLA absorbed from foods is risk-free; Children ages 12 and under; Liver problems. Main constituents Mixture of active molecules sharing the same chemical composition, with slightly different structures; mostly cis-9, trans and trans, cis isomers of linoleic acid Main dietary sources of CLA: Meat from ruminants lamb, beef, mutton, goat , milk, and other dairy products.

Sources for the production of CLA supplements: Vegetable oils transformed by chemical reactions. Lipid substrates such as corn oil has shown to increase CLA content of milk by providing more unsaturated fatty acids for biohydrogenation.

When cows were fed both corn oil and fish oil in combination, CLA content in milk increased ten-fold Table 4. The CLA content of meat from ruminant animals is generally less than the CLA in dairy products Table 1.

Grass fed beef tends to have small increases in CLA compared to grain fed. However, if grass fed beef are finished on higher grain diets prior to slaughter, the CLA content in meat decreases.

In general, diet has a small effect on CLA in beef compared to the dietary influence on dairy products. The potential benefit of CLA in human health is the major reason for the excitement and interest in CLA.

The major interest surrounding CLA is the anti-carcinogenic or anti-cancer effects. The National Academy of Science publication entitled "Carcinogens and Anti-carcinogens in the Human Diet stated that "conjugated linoleic acid is the only fatty acid shown unequivocally to inhibit carcinogenesis in experimental animals.

CLA can reduce new tumor growth and destroy existing tumor cells. CLA has killed existing cancer cells in colon, ovarian and prostate carcinoma, leukemia, melanoma, and breast tumors. In addition to the anti-carcinogenic properties, other positive health benefits demonstrated in animal models include:.

Although much research has been conducted with laboratory animals, specific studies comparing risk of cancer and CLA consumption by humans have been limited to date.

Caution is needed when applying these results to humans. However, an epidemiological study in Finland revealed that as women consumed more dairy products, the risk of breast cancer dropped. Researchers concluded there was a "protective effect" associated with milk.

A study in France showed an inverse relationship between CLA concentrations in milk and the risk of severity of breast cancer. As research continues on many fronts, the specific physiological effects and the responses will be better defined.

This document illustrates the feasibility of producing CLA enriched milk and meat. An important question is whether the increase achieved will translate into a real benefit for the person consuming the milk. Extrapolation from animal studies suggests that humans may need to consume about 3 g of CLA per day.

Using the CLA percentages in Table 1, one serving of whole milk plus a sandwich with butter and cheddar cheese will provide about 1. To achieve 3 g intake of CLA per day intake, modifying the diet of dairy cows to increase CLA in milk and increased consumption of higher fat dairy products would be needed.

The concept of enhancing the levels of health promoting fatty acids in food is not new. One example of this has been the introduction of eggs enriched in omega-3 fatty acids. This recognizes the trend among consumers is toward an increased desire to make diet choices that promote good health. Consumers could increase their CLA intake by taking synthetic CLA in pill form, which is available in health food stores.

However, the main difference between the CLA in these products and CLA in milk is the broader range of isomers in the synthetically produced CLA.

The relative value for human health of this range of CLA isomers compared to the CLA found in ruminant milk fat is uncertain. However, most of these isomers are not thought to have anti-carcinogenic properties.

Nevertheless, CLA-enriched milk produced through manipulation of the ration fed to cows has an advantage over this type of product in that it can be promoted as a "natural" source of CLA.

It may also be easier for CLA-enriched milk to gain acceptance since milk already has a wide distribution and consumers are accustomed to seeing a broad variety of dairy products in the grocery stores. A challenge will be in overcoming the existing public perception regarding milk fat and health.

CLA-enriched milk may be attractive to those consumers who have abandoned milk and milk products, such as butter, due to concerns over the impact of milk fat on their health.

However, the introduction of new products like CLA-enriched milk does require significant investment in marketing and there are no guarantees that the product will attract sufficient consumer interest to be viable. The incentive for producers to feed special diets needed to enhance CLA levels may require a higher price for the milk.

The presence of a compound CLA in ruminant fat with such potent health promoting effects has been an unanticipated discovery. The ability to enhance the concentration of CLA through manipulation of the dairy ration demonstrates the feasibility of producing CLA enriched dairy products.

As consumers become more conscious of the link between diet and health, milk designed to have enhanced levels of CLA may provide new market opportunities for milk and milk products such as butter and cheese.

The store will not work correctly when cookies are disabled. Conjugated Linoleic Acid CLA in Animal Production and Human Health. CLA inhibits cancer by blocking the growth and metastatic spread of tumours. CLA is fast acting, and begins to inhibit both malignant and benign tumours almost immediately [ 15 ].

Kritchevsky [ 72 ] reviewed the inhibitory effects of CLA on chemically-induced skin, stomach, mammary or colon tumours in mice and rats. In vitro studies in murine myeloid leukaemia WEHI-3B JCS [ 73 ] and human colorectal HT, MIP and prostate PC-3 colorectal [ 74 ] cells, as well as in vivo human studies on breast [ 75 , 76 ] and prostate [ 42 ] cancers showed CLA's best antiproliferative effects.

Cellular mechanisms of modulation of carcinogenesis by CLA are numerous and complex. It may be via reduction in cell proliferation [ 77 , 78 ], lipid oxidation [ 5 ], vitamin A [ 79 ] and prostaglandin PG [ 80 , 81 ] metabolisms.

It is also possible that CLA may interfere with cell transformation through signal transduction [ 82 ]. Furthermore, the anticarcinogenic properties of CLA are, at least partially, attributed to thier ability to interrupt the n-6 PUFA metabolic pathway for the biosynthesis of eicosanoids, including PGs [ 80 , 81 ].

Altered phospholipid-associated fatty acid metabolism and eicosanoid carbon derivatives viz , PGs, thromboxanes, leukotrienes, hydroxyeicosatetraenoic acids formation are yet other thrust areas of active research. Eicosanoids modulate cell proliferation, inflammation, local and systemic immunity, platelet aggression and tissue diffrentiation.

Free CLAs could compete with other fatty acids to be incorporated in the phospholipids and modifies subsequent eicosanoid production. Dietary CLA reduce PG-E2 [ 83 ] and others PGF 2α , leukotriene-B 4 , leukotriene-C 4 derived from arachidonic acid metabolism [ 29 , 84 , 85 ].

Other possible route for the CLA mediated reduction of arachidonate-derived eicosanoids is through inhibition of cyclooxygenase COX 1 and 2.

Necrosis generally result from insult or toxicity reaction and triggers inflammation, whereas apoptosis is a distinct energy requiring process of programmed cell death, characterised by DNA fragmentation, chromosome condensation, nuclear fragmentation, formation of apoptotic bodies, and inversion of phosphatidylserine in the plasma membrane [ 86 ].

It is expected that CLA could reduce cell proliferation by blocking DNA synthesis [ 87 ] and cell cycle proteins [ 42 , 88 ] that regulate this process, and that CLA may support elevated apoptosis primarily by suppressing the expression of antiapoptotic bcl-2 gene [ 29 ].

With different cell lines, CLA was able to increase the IL-2 and IFN-γ via modulation of protein kinase activity and production of oxidant species, which significantly inhibited proliferation [ 89 ], and it appears to be the function of relative content of specific isomers and their ability to elicit a p53 response that leads to cell growth arrest by inhibiting the expression of factors required for G1 to S-phase transition including cyclins D1 and E [ 90 ], or by the inhibition of the insulin-like growth factor-I receptor signalling pathway [ 87 ].

Atherosclerosis is a progressive disease of medium and large arteries by the accumulation of lipids in the inflammatory cells foam-cell formation , cellular proliferation, platelet adherence and aggression, and calcium deposition [ 91 , 92 ].

CLA are a potent anti-atherogenic dietary fatty acid in animal models of atherosclerosis by activating PPARs [ 93 , 94 ]. One would expect a decrease in atherogenic lipoprotein plasma levels such as very low, LDL-cholesterols and increase in anti-atherogenic high density lipoprotein cholesterol HDL through increases in apo A-I and apo A-II synthesis; b overexpression in HDL receptors capable of increasing cellular cholesterol efflux; and c decrease in vascular inflammation by repressing nuclear NF k B and apo A-I transcriptional activity and they would reduce thrombosis risk by inhibiting tissue factor and fibrinogen synthesis [ 59 , 95 ].

Despite a few studies [ 5 , 40 , 43 , 96 ], no conclusive evidences involving CLA isomers are available to substantiate the above signalling pathways proposed for drugs. Interestingly, ratios of the LDL cholesterol to HDL cholesterol and total cholesterol to HDL cholesterol were significantly reduced in CLA-fed rabbits with less atherosclerosis [ 36 , 62 ].

Diabetes can be caused by too little insulin type I , resistance to insulin type II , or by both. Supplementing the diet with CLA may lead to better disease management in diabetics, especially type II.

Many studies strongly suggest that the CLA isomer may be the bioactive isomer of CLA to influence the body weight changes observed in subjects with type II diabetes, reviewed by Belury et al.

Brown et al. observed that during delipidation process, CLA exerts a cascade of molecular actions by down regulating the expression of PPAR γ and its downstream targets that are critical for fatty acid and glucose metabolism, which eventually inhibits glucose and fatty acid uptake and metabolism.

Studies investigating the mechanisms by which CLA operates at the cellular level show that the primary targets for CLA are members of the nuclear receptor family, particularly the lipostat transcription factors; viz PPARα, PPARγ, SREBP1c, and LXRα [ 38 , 41 ].

Consequently, the effects of CLA on glucose metabolism are likely secondary effects mediated through factors such as PPARγ coactivator 1[ 98 ] that are controlled by these nuclear receptors.

Or it could be due to complex mechanisms by the regulation of the expression of genes like uncoupling proteins important in the regulation of adipogenesis, glucose and lipid metabolism, and, perhaps, whole-body thermogenesis [ 99 ].

Another possible action of CLA in alleviating hyperinsulinemia in Zucker diabetic fatty rats is via the sensitisation of the adiponectin, a recently discovered hormone secreted by adipocytes that has been reported to enhance insulin sensitivity [ ].

Furthermore, determining the ability of CLA isomers to influence glucose and lipid metabolism as well as markers of insulin sensitivity is imperative to understanding the role of CLA, and thus to aid in the management of type II diabetes and other related conditions of insulin resistance [ , ].

In vitro studies of the use of immune cells and in vivo animal models demonstrate that CLA modulate immune function. However, in contrast to the reports with animal models, CLA feeding to young healthy women did not alter any of the indices of immune status tested, and it suggests that short-term CLA supplementation in healthy volunteers is safe, but it does not have any added benefit to their immune status [ ].

Ringseis et al. found that CLA inhibit TNFα-induced eicosanoid release from human vascular smooth muscle cells with the interaction of PPARγ [ ].

Reports demonstrate that both the active CLA isomers 9- and CLAs can elicit both the innate and adaptive immune responses [ — ]. These effects lie in the ability of CLAs to modify soluble factors or mediators of immunity such as eicosanoids [ ], cytokines [ ] and immunoglobulin production [ , ].

Albers et al. They found that ratio beneficially enhanced the protective antibody levels to hepatitis B. CLA may alter eicosanoid signalling via TNF-α, and thus affecting a range of biological functions including antigen presentation [ 19 ].

This would cause changes in the membrane characteristics and changes in the activity of membrane proteins that serve as ion channels, transporters, receptors, signal transducers or enzymes [ 86 ]. The alternative hypothesis is rooted in the fundamental PPAR-mediated signalling, via expression of target genes involved in immune function [ 19 ].

CLA can also protect against tissue breakdown due to immune stimulation during periods of severe illness [ , ]. This effect may be due to the modulation of NF k B for negatively regulating the lipopolysaccharide-induced inflammatory responses [ ], or against the catabolism and inflammatory effects induced by cytokines, especially TNFα [ 19 ].

The immunomodulatory effects of CLA may have application in livestock production as an alternative to the use of feed antibiotics functional food , or as a means of improving the response to vaccination and conferring disease resistance.

Song et al. Interestingly, levels of plasma IgA and IgM were increased with decreased plasma IgE levels. CLA supplementation also decreased the levels of the proinflammatory cytokines, TNF-α and IL-1β, but increased the levels of the anti-inflammatory cytokine, IL In addition to these effects, delayed type of hypersensitivity response was decreased during and after CLA supplementation, coupled with no significant changes for plasma glucose, lipids, lymphocyte morphology.

Very recently, Kwak et al. observed in obese pre-menopausal Korean females that CLA 9- and CLA mixture supplementation modulated to the increased release of markers C-reactive protein, IL10, IgM related with inflammation and immune function, and this effect was much more subtle than those found in animals and few other clinical studies [ ].

Mixed CLA isomers have been shown to have variable effects on bone formation ostheosynthesis and resorption in animals. The variable effects of CLA on bone physiology may be due to the different isomers present in common commercial preparations of CLA, and the effects of the predominant individual isomers 9- and CLAs are not clear.

Dietary CLA inhibits eddosteal bone resorption, increases endocortical bone formation, and modulates the action and expression of COX enzymes, thereby decreasing prostaglandin-dependent bone resorption [ , ]. CLA also enhances calcium absorption from diet, improve bone formation and reduce the rate of bone resorption in adult OVX rats [ ].

Since CLA can affect inflammatory cytokines, it is hypothesized that CLA may be a good tool for prevention or reduction of rheumatoid arthritis symptoms in humans [ ].

However, under the conditions tested in this double-blind, placebo-controlled trial in adult men, a CLA supplement of mixed isomers did not affect markers of calcium or bone metabolism [ ]. Doyle et al. Baseline levels of these biochemical parameters were similar in both groups of subjects.

While the placebo had no effect, CLA supplementation resulted in a three-fold increase in 9-CLA isomer in total plasma lipids [ ].

Platt et al. have found that alkaline phosphatase activity in cell lysates as a marker of early osteoblast differentiation in human osteoblast-like cells [ ]. The 9-CLA increased the number and size of mineralized bone nodules from 25 to μM, but the CLA did not show such effect [ ].

The increase in mineralized bone nodule formation by 9-CLA was accompanied by a variable increase in alkaline phosphatase activity. These results show that the 9-CLA increases the formation of mineralized bone nodules using bone cells of human origin, and provide evidence for isomer-specific effects of CLA on bone health [ ].

Though only positive health benefits of CLA have been addressed here, some negative impacts of CLA could not be ruled out [ ]. Some human CLA supplementation studies have often shown conflicting and less convincing health benefits.

The marked variations between studies may reflect the isomer-specific effects of individual CLA isomers, which can often have opposing effects [ 36 ]. Main findings from the mice models are increased liver and spleen weight [ 16 , 26 ] and insulin resistance [ 41 , 98 ].

CLA-induced fatty liver hemorrhagic syndrome in birds [ ] is yet another facet. A major problem arising from human studies related mainly to the gastrointestinal tract; data indicate that CLA can act as a cancer promoter in colon carcinogenesis, possibly through pathways affecting NF k B and cyclin D1 [ ].

Though CLA profoundly decreased body fat in mice possibly through increased energy expenditure, dietary CLA greatly increased the activity and mRNA levels of various lipogenic enzymes like hepatic Δ 5 - and Δ 6 - desaturases and SREBP-1 in the liver [ ].

A large increase in lipogenesis and accumulation of triacylglycerol in the liver after CLA treatment may represent the physiological response of the animal to metabolize excess glucose to fatty acid for storage as triacylglycerols in liver rather than in adipose tissue [ ].

Therefore, there is a possibility that the counteraction of CLA-mediated induction of hepatic lipogenesis aggravates glucose intolerance and hyperinsulinemia, despite being potentially effective in preventing fatty liver [ ].

In obese men, CLA induces hyperproinsulinemia that is related to impaired insulin sensitivity hyperinsulinaemic-euglycaemic clamp , independently of changes in insulin concentrations [ ]. As hyperproinsulinemia predicts diabetes and cardiovascular diseases, the use of weight-loss supplements containing CLA cautions its indiscriminate consumption.

Moreover, such studies need to be duplicated in other labs giving emphasis to men and women, age groups, ethnic background, or food style.

The possible beneficial effects of CLA supplementation in decreasing body fat mass have received a great deal of attention, but potential adverse effects of CLA on the insulin balance have been largely ignored [ 69 ].

This is paradoxical, because CLA-mediated hyperinsulinemia has been observed in several studies in mice. CLA-induced insulin resistance may be related to the alterations of plasma leptin levels.

Studies have shown that CLA supplementation induced reductions of plasma leptin levels in various animal models [ 69 ]. The inconclusive results in human supplementation trials are due to the use of mixed isomers, which may negate one another, resulting in no net change in adiposity; moreover, doses used in human trials were much lower than those used in animal studies [ 62 ].

These paradoxical findings may arise from the use of mixed isomers of CLA or the difference in experimental models used. In any event, isomer-specific dose-titrated clinical studies combined with mechanistic studies in cultures of primary cells should provide the much needed insight on potential human applications for CLA.

Within various rodent species and strains, dietary CLA exerts varying potencies; therefore, the differences in species' sensitivities are of great importance when trying to extrapolate rodent data to the human situation [ 2 , 15 ].

Of late, over a hundred clinical studies regarding the efficacy of CLA as functional food are available in literature. A brief survey on the outcome of such studies shows that the overwhelming beneficial effects of CLA impart positive outlook.

Table 2 [ , — ] gives some of the notable effects of CLA in humans, as evidenced by clinical studies. It seems that 9- and CLA are having contrasting biological functions, but CLA with more detrimental effects. However a ratio of these isomers may give better effect, as effected in immune function [ ].

Normal CLA concentration in human body is 0. Studies reveal that an intake of about g per day for 6 to 12 months by an adult would impart optimum biological effects, which would be long lasting too [ ]. According to Fernie et al. Very recently Kelley et al.

demonstrated in mice that some adverse effects like insulin resistance and non-alcoholic fatty liver disease attributed to CLA may be due to the deficiency of n-3 PUFA and that such adverse effects can be corrected by a concomitant increase in the intake of α-linolenic acid, an n-3 PUFA and flax seed oil, a rich natural source for this fatty acid [ ].

Considering the reported adverse events and safety concerns, Gaullier at al. assessed the effects of supplementation of 3. The data revealed that CLA supplementation for 24 months in healthy, overweight adults was well tolerated as revealed by the decreased body weight and body fat mass, and increased circulating lipoprotein, thrombocytes, and aspartate amino transferase.

There was no change in fasting blood glucose. Plasma total cholesterol and LDL cholesterol were reduced, whereas HDL cholesterol and triglycerides were unchanged. The reported adverse effect rate was decreased considerably in the 2-years long study, compared with the initial 12 months of the study [ ].

These results indicate that most of the reported adverse effects are related to the short-term studies in humans [ ]. Apparently, many of the physiological adverse effects like hyperinsulinemia and fatty liver in mice were ameliorated with the inclusion of increasing amounts of fish oil in the diets, which is a rich source for very long-chain fatty acids [ ].

These results indicate that a mixture comprising all n-3, n-6 CLA and n-9 fatty acids in an appropriate proportion on humans would be a better answer to avoid the reported adverse effects of CLA. Obese people are likely to consume more of these minor lipid nutrients, irrespective of their high cost.

Although comparatively few human clinical studies exist, it appears to date that CLA are beneficial for human health. More focused world-wide network clinical trials involving probands and patients from all continents are required to arrive at conclusive evidence.

Another important aspect is contrasting functionalities of CLA isomers and the fact that a majority of clinical trials use a crude mixture of CLA predominated by 9- and CLAs. Moreover, the reported negative effects like fatty liver and spleen, induction colon carcinogenesis, are yet to be proved beyond doubt.

Furthermore, apart from PPAR-mediated signalling, more conclusive evidences are necessary to unravel other molecular mechanisms and complex signalling pathways triggered by dietary CLA.

Strictly controlled studies as performed in animals or in culture models may not be maintained in clinical trials, however, most of human studies are based on blood, blood cells, milk or biopsy specimens - all these would cause probable variations in the general data generated.

Thus, conclusive studies focused on parameters such as type of CLA isomer administered, variables measured, mode of administration eg.

To this end, a positive result is that recent studies emphasise a combination of CLA with PUFA to be best formula to ameliorate the adverse effects observed so far. Steinhart H, Rickert R, Winkler K: Identification and analysis of conjugated linoleic acid isomers CLA. Eur J Med Res. CAS Google Scholar.

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Most people already ingest some CLA through their diet. The average intake in the US is about mg per day for women and mg for men Keep in mind that the CLA you find in supplements is not derived from natural foods but made by chemically altering linoleic acid found in vegetable oils The balance of the different forms is heavily distorted in supplements.

They contain types of CLA never found in large amounts in nature 12 , The main dietary sources of CLA are dairy and meat from cows, goats and sheep, whereas CLA supplements are made by chemically altering vegetable oils. The biological activity of CLA was first discovered by researchers who noted that it could help fight cancer in mice Later, other researchers determined that it could also reduce body fat levels As obesity increased worldwide, interest grew in CLA as a potential weight loss treatment.

Animal studies suggest that CLA may reduce body fat in several ways In mouse studies, it was found to reduce food intake, increase fat burning, stimulate fat breakdown and inhibit fat production 17 , 18 , 19 , CLA has also been studied extensively in randomized controlled trials, the gold standard of scientific experimentation in humans — though with mixed results.

Some studies indicate that CLA can cause significant fat loss in humans. It may also improve body composition by reducing body fat and increasing muscle mass 21 , 22 , 23 , 24 , However, many studies show no effect at all 26 , 27 , In a review of 18 controlled trials, CLA was found to cause modest fat loss The effects are most pronounced during the first six months, after which fat loss plateaus for up to two years.

According to this paper, CLA can cause an average fat loss of 0. kg per week for about six months. Another review gathered that CLA caused about 3 pounds 1. While these weight loss effects may be statistically significant, they are small — and there is potential for side effects. Though CLA supplements are linked to fat loss, the effects are small, unreliable and unlikely to make a difference in everyday life.

Many long-term observational studies have assessed disease risk in people who consume larger amounts of CLA. Notably, people who get a lot of CLA from foods are at a lower risk of various diseases, including type 2 diabetes and cancer 31 , 32 , Additionally, studies in countries where cows predominantly eat grass — rather than grain — show that people with the most CLA in their bodies have a lower risk of heart disease However, this lower risk could also be caused by other protective components in grass-fed animal products, such as vitamin K2.

Of course, grass-fed beef and dairy products are healthy for various other reasons. Many studies show that people who eat the most CLA have improved metabolic health and a lower risk of many diseases. However, the CLA found in supplements is made by chemically altering linoleic acid from vegetable oils.

They are usually of a different form than the CLA found naturally in foods. Supplemental doses are also much higher than the amounts people get from dairy or meat. As is often the case, some molecules and nutrients are beneficial when found in natural amounts in real foods — but become harmful when taken in large doses.

Sources for the production of CLA supplements: Vegetable oils transformed by chemical reactions. Close medical supervision is therefore necessary for diabetics. The information contained on the familiprix. com site is for informational purposes only and does not in any way replace the advice and advice of your pharmacist or any other health professional.

The aim of the present study was to determine the absorption efficiency, incorporation and metabolism of a mixture of conjugated α-linolenic acid in growing rats under nutritional and physiological conditions.

No significant differences on the total diet consumption were observed among the four groups. At the end of the feeding period, the weights of the animals were not significantly different, ± 6 means ± SD ; ± 10 in groups fed RA and CLnAs as FFA and ± 7; ± 6 in groups fed the RA and the CLnAs as TAG.

Table 2 shows the apparent digestibility efficiency for total fatty acids and for each fatty acid. Digestibility of total fatty acid was not significantly different between the four experimental groups. Each group had a lower absorption of saturated fatty acids compared to monounsaturated and polyunsaturated fatty acids.

RA and CLnA have been totally absorbed as FFA and TAG suggesting that under these conditions, there is no difference in absorption. The main fatty acids in liver, plasma and adipose are presented in Table 3. RA and CLnA accumulated preferentially in neutral lipids. No major differences between RA and CLnA accumulation were seen whatever the dietary form, FFA or TAG.

On the other hand, slight differences were found in monounsaturated fatty acids of the liver neutral lipids between rats fed the FFA form of RA and CLnA.

The animals fed CLnA as FFA had lower content of arachidonic acid in liver and plasma PL. CLnA metabolites are shown in Table 4. The cis -9, trans , cis was elongated and desaturated up to cis -4, cis -7, cis , cis , trans , cis while the cis -9, trans , cis was metabolized up to cis -5, cis -8, cis , trans , cis Conjugated metabolites accumulated in both neutral lipids and polar lipids.

However, the cis -7, cis , cis , trans , cis and the cis -4, cis -7, cis , cis , trans , cis were exclusively detected in liver and plasma phospholipids.

No differences in the amount of the metabolites were found between the two dietary forms given FFA or TAG. This suggests that there was no difference in the metabolic fate elongation and desaturation of CLnA when ingested as FFA and as TAG. Most of the studies so far published on CLA focussed on their putative effects on biological function and prevention of metabolic disorders.

However, few studies considered the effect of the dietary form FFA or TAG on their bioavailabilty and metabolism [ 6 ], while dietary supplement are often available as free fatty acids.

The major reason may be that TAG are more expensive. Otherwise, no studies have shown their absorption efficiency in nutritional conditions. In the present study, the experimental fatty acids RA and CLnA mixture were given as FFA or as randomized TAG and were equally incorporated into tissues Table 2.

No significant differences in absorption levels were found between those two lipid forms. This suggests that the dietary form did not modify the incorporation of RA and of CLnA into tissues under our experimental conditions.

These data are in agreement with the study of De Schrijver et al. While in the present study RA and CLnA were totally absorbed, a previous study using lymphatic recovery showed that a CLA mixture given as FFA was less absorbed than linoleic acid [ 11 ].

No study was so far published on the lymphatic recovery of CLnA. However, it has already been shown that RA absorption as TAG did not behave like a common fatty acid because of its conjugated structure or its trans double bound in Δ 11 position or both [ 13 ].

In the present study, we also demonstrate that CLnA mixture is preferably incorporated into neutral lipids similar to RA. The incorporation of trans fatty acids in NL has long time been demonstrated with elaidic acid trans -9 and shows that it follows the metabolic pathway of saturated fatty acids [ 14 ].

Moreover, it has been hypothesized by Martin et al. This hypothesis was also sustained by Banni et al. CLnA competes as well for this enzyme as seen by the lower arachidonic acid content in liver PL in rats fed CLnA.

Metabolites from both CLnA isomers were found in NL as in PL. The cis -9, trans , cis isomer was elongated and desaturated up to n-3 conjugated isomer while cis -9, trans , cis was elongated and desaturated up to n-3 conjugated isomer.

The conjugated isomers of n-3 and n-3 were found exclusively in polar lipids of liver and plasma while the RA metabolites were found in neutral lipids as demonstrated by Sebedio et al. This shows that conjugated metabolites of cis -9, trans , cis could interfere in the fatty acid composition of membranes which affect their properties such as fluidity and permeability.

Other studies are needed to confirm this hypothesis. This study demonstrated that an equimolar mixture of two CLnA isomers, cis -9, trans , cis and cis -9, trans , cis has the same apparent absorption efficiency than RA when ingested under nutritional and physiological conditions.

Both CLnA isomers are mainly incorporated into neutral lipids. The biological impact of the ingestion of these fatty acids has to be considered as they could interfere with lipid metabolism. Free fatty acids of conjugated linoleic acid CLA and conjugated linolenic acid CLnA were gratefully provided by Naturia Inc.

Sherbrooke, Canada. The high oleic sunflower oil and the linseed oil were purchased from Lesieur Asnières, France and Robbe Compiègne, France , respectively. All solvents were purified by distillation before utilization. TAG of CLA and CLnA were synthesized as described by Kodali et al.

The initial weight of the animals was 82 ± 7 g. They were adapted during 4 days with a semi-liquid diet see below before being allocated to one of the 4 dietary groups see below. Six animals were allocated to each group.

The average starting weight in each group was ± 1 g. At the end of the 8 days experimental period, the animals were fasted for 16 hours and weighted. They were then anesthetised with isofurane and exsanguinated by abdominal aortic blood puncture. The plasma was then collected and stored at °C until lipid extraction and analysis.

The experimental diets were fed in a semi-liquid form in order to facilitate the determination of food consumption. CLA and CLnA were studied as FFA and TAG. The fatty acid content of each diet is summarized in Table 1.

Food was exchanged every two days. At that time, the remaining semi-liquid food was removed and weighed to determine food intake. The animals were weighed twice per times a week. The faeces were collected each day, pooled and frozen at °C.

Before being lyophilized, the total faeces collected from each rat were frozen at °C for 24 h. The dried faeces were cleared of impurities, weighted and crushed with a ball crusher.

The extract was then evaporated to dryness and left for one night under vacuum in a dessicator. The total lipid extract was then weighted and dissolved in chloroform in gauge flask for conservation at °C. The apparent digestion efficiency ADE was calculated as follow [ 22 ].

The quantification of each fatty acid in the faeces was done by GC analysis of their methyl esters using an internal standard Thus, the total fecal lipids were saponified under mild conditions before methylation. The solutions were left in the dark at room temperature for 16 h. The solution was centrifuged at g for 3 minutes.

The resulting FAME were then analysed by GC using a Hewlett-Packard serie II gas chromatograph equipped with a BPX70 capillary column SGE, Melbourne, Australia, m × 0.

FAME were identified using authentic standards and quantitative data were obtained using the Diamir software JMBS Developments, Le Fontanil, France.

Clin Chim Acta. Download references. The authors wish to thank Pierre Juanéda for statistical analyses. The authors are also grateful to Fonds Québécois de Recherche sur la Nature et les Technologies FQRNT and Naturia Inc Sherbrooke, Canada for a Ph.

D scholarship to M. INRA-Université d'Auvergne, Laboratoire de Nutrition Humaine, 63 , Clermont-Ferrand, France. You can also search for this author in PubMed Google Scholar. Correspondence to Jean-Louis Sébédio. MP carried out the experimental study, a part of the lipid analysis and drafted the manuscript, JPS participated in the design and the coordination of the study and carried out the experimental study, JMC participated in the design and the conceive of the study and helped to draft the manuscript, SG carried out lipid analysis, PA participated in the design of the study and helped to drafted the manuscript, JLS participated in the design, the conceive and the coordination of the study and helped to draft the manuscript.

Open Access This article is published under license to BioMed Central Ltd. Reprints and permissions. Plourde, M. et al. Absorption and metabolism of conjugated α-linolenic acid given as free fatty acids or triacylglycerols in rats. Nutr Metab Lond 3 , 8 Download citation.

Received : 12 October Accepted : 20 January Published : 20 January Anyone you share the following link with will be able to read this content:. Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative.

Skip to main content. Search all BMC articles Search. Download PDF. Download ePub. Abstract Background Conjugated linoleic acid CLA is a group of polyunsaturated fatty acids which have been extensively studied in the past two decades.

Results Male Wistar rats were fed rumenic acid RA: cis -9, trans and a CLnA mixture cis -9, trans , cis and cis -9, trans , cis as FFA and TAG for 8 days. Conclusion Finally, CLnA are as well absorbed as RA in vivo and their incorporation into tissues and bioconversion are similar when ingested as FFA or as TAG.

Background Conjugated linoleic acid CLA is a group of polyunsaturated fatty acids PUFA found in ruminant meat about 0. Figure 1. Structure of both isomers included in the CLnA mixture compared to rumenic acid. Full size image. Effects of dietary fat on fatty acid digestibility and absorption Table 2 shows the apparent digestibility efficiency for total fatty acids and for each fatty acid.

Results are expressed as means SD of 6 determinations. Full size table. Discussion Most of the studies so far published on CLA focussed on their putative effects on biological function and prevention of metabolic disorders.

Conclusion This study demonstrated that an equimolar mixture of two CLnA isomers, cis -9, trans , cis and cis -9, trans , cis has the same apparent absorption efficiency than RA when ingested under nutritional and physiological conditions.

Methods Fatty acids Free fatty acids of conjugated linoleic acid CLA and conjugated linolenic acid CLnA were gratefully provided by Naturia Inc. Triacylglycerol TAG synthesis All solvents were purified by distillation before utilization. Diets The experimental diets were fed in a semi-liquid form in order to facilitate the determination of food consumption.

Faeces lipid extraction and analysis Before being lyophilized, the total faeces collected from each rat were frozen at °C for 24 h. References Fritsche J, Rickert R, Steinhart H, Yurawecz MP, Mossoba MM, Kramer JKG, Ku Y: Conjugated linoleic acid CLA isomers: formation, analysis, amounts in foods, and dietary intake.

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Acknowledgements The authors wish to thank Pierre Juanéda for statistical analyses. View author publications. Additional information Competing interests The author s declare that they have no competing interests.

Authors' contributions MP carried out the experimental study, a part of the lipid analysis and drafted the manuscript, JPS participated in the design and the coordination of the study and carried out the experimental study, JMC participated in the design and the conceive of the study and helped to draft the manuscript, SG carried out lipid analysis, PA participated in the design of the study and helped to drafted the manuscript, JLS participated in the design, the conceive and the coordination of the study and helped to draft the manuscript.

Rights and permissions Open Access This article is published under license to BioMed Central Ltd. About this article Cite this article Plourde, M.

However, if grass fed beef are finished on higher grain diets prior to slaughter, the CLA content in meat decreases. In general, diet has a small effect on CLA in beef compared to the dietary influence on dairy products. The potential benefit of CLA in human health is the major reason for the excitement and interest in CLA.

The major interest surrounding CLA is the anti-carcinogenic or anti-cancer effects. The National Academy of Science publication entitled "Carcinogens and Anti-carcinogens in the Human Diet stated that "conjugated linoleic acid is the only fatty acid shown unequivocally to inhibit carcinogenesis in experimental animals.

CLA can reduce new tumor growth and destroy existing tumor cells. CLA has killed existing cancer cells in colon, ovarian and prostate carcinoma, leukemia, melanoma, and breast tumors.

In addition to the anti-carcinogenic properties, other positive health benefits demonstrated in animal models include:.

Although much research has been conducted with laboratory animals, specific studies comparing risk of cancer and CLA consumption by humans have been limited to date. Caution is needed when applying these results to humans. However, an epidemiological study in Finland revealed that as women consumed more dairy products, the risk of breast cancer dropped.

Researchers concluded there was a "protective effect" associated with milk. A study in France showed an inverse relationship between CLA concentrations in milk and the risk of severity of breast cancer. As research continues on many fronts, the specific physiological effects and the responses will be better defined.

This document illustrates the feasibility of producing CLA enriched milk and meat. An important question is whether the increase achieved will translate into a real benefit for the person consuming the milk. Extrapolation from animal studies suggests that humans may need to consume about 3 g of CLA per day.

Using the CLA percentages in Table 1, one serving of whole milk plus a sandwich with butter and cheddar cheese will provide about 1. To achieve 3 g intake of CLA per day intake, modifying the diet of dairy cows to increase CLA in milk and increased consumption of higher fat dairy products would be needed.

The concept of enhancing the levels of health promoting fatty acids in food is not new. One example of this has been the introduction of eggs enriched in omega-3 fatty acids. This recognizes the trend among consumers is toward an increased desire to make diet choices that promote good health.

Consumers could increase their CLA intake by taking synthetic CLA in pill form, which is available in health food stores.

However, the main difference between the CLA in these products and CLA in milk is the broader range of isomers in the synthetically produced CLA.

The relative value for human health of this range of CLA isomers compared to the CLA found in ruminant milk fat is uncertain. However, most of these isomers are not thought to have anti-carcinogenic properties.

Nevertheless, CLA-enriched milk produced through manipulation of the ration fed to cows has an advantage over this type of product in that it can be promoted as a "natural" source of CLA. It may also be easier for CLA-enriched milk to gain acceptance since milk already has a wide distribution and consumers are accustomed to seeing a broad variety of dairy products in the grocery stores.

A challenge will be in overcoming the existing public perception regarding milk fat and health. CLA-enriched milk may be attractive to those consumers who have abandoned milk and milk products, such as butter, due to concerns over the impact of milk fat on their health.

However, the introduction of new products like CLA-enriched milk does require significant investment in marketing and there are no guarantees that the product will attract sufficient consumer interest to be viable.

The incentive for producers to feed special diets needed to enhance CLA levels may require a higher price for the milk. The presence of a compound CLA in ruminant fat with such potent health promoting effects has been an unanticipated discovery.

The ability to enhance the concentration of CLA through manipulation of the dairy ration demonstrates the feasibility of producing CLA enriched dairy products.

As consumers become more conscious of the link between diet and health, milk designed to have enhanced levels of CLA may provide new market opportunities for milk and milk products such as butter and cheese.

The store will not work correctly when cookies are disabled. Conjugated Linoleic Acid CLA in Animal Production and Human Health. Conjugated linoleic acid CLA occurs naturally in ruminant milk fat and meat, but diet changes can affect the amounts. Save for later Print Share.

Updated: January 3, Skip to the end of the images gallery. Mixture of active molecules sharing the same chemical composition, with slightly different structures; mostly cis-9, trans and trans, cis isomers of linoleic acid. Pregnancy potentially lower birth weight in newborns.

Please note that CLA absorbed from foods is risk-free; Children ages 12 and under; Liver problems. Main constituents Mixture of active molecules sharing the same chemical composition, with slightly different structures; mostly cis-9, trans and trans, cis isomers of linoleic acid Main dietary sources of CLA: Meat from ruminants lamb, beef, mutton, goat , milk, and other dairy products.