CLA and body weight regulation in humans

CLA comprises a group of unsaturated FA isomers with a variety of biological effects in experimental animals. CLA reduces body fat accumulation in animal models and has been suggested to have significant effects on lipid and glucose metabolism, e.g., antidiabetic effects in obese Zucker rats. It has been proposed that the trans10-cis12 isomer is the active isomer associated with the antiobesity and insulin-sensitizing properties of CLA. The metabolic effects in humans in general, and isomer-specific effects specifically, are not well characterized. In a series of controlled studies in humans, we investigated the effects of CLA (given as the commercially available mixture of isomers and as the purified trans10-cis12 CLA isomer) on anthropometry, lipid and glucose metabolism, and markers of lipid peroxidation. Preliminary results indicate that CLA may slightly decrease body fat in humans also, particularly abdominal fat, but there is no effect on body weight or body mass index. There is no simultaneous improvement in lipid or glucose metabolism. Rather, the trans10-cis12 CLA isomer unexpectedly caused significant impairment of the peripheral insulin sensitivity as well as of blood glucose and serum lipid levels. In addition, CLA markedly elevated lipid peroxidation. Thus, the metabolic effects of CLA in human seem complex; further studies, especially of isomer-specific effects and for longer time periods, are warranted.     

High intake,but not low intake,of CLA impairs weight gain in growing mice

CLA has a range of biological properties, including effects on lipid metabolism and body composition in experimental animals. The prevalent isomer of CLA found in the human diet is 9c, 11t-CLA, and it is predominantly found in products containing fat from ruminant animals. This study investigated the effect of dietary CLA on energy balance in mice. Synthetic CLA reduced body fat in growing male BAI B/c mice in a dose-dependent manner over the range 0.25–1.0% w/w CLA in the diet. Weight gain was also reduced at the highest levels of dietary CLA, being only 5.88±2.68 g/4 mice (mean±1 SD) after 4 wk of 2.0% CLA in the diet, compared with weight groups. There was no significant effect on weight gain if diets contained 0.5% synthetic CLA or less. These results suggest that high levels of a synthetic mixture of CLA isomers modify energy metabolism and body composition and that high levels of synthetic CLA impair weight gain and reduce body fat pad mass in growing mice.     

Influence of conjugated linoleic acids on body composition and selected serum and endocrine parameters in resistance‐trained athletes

Conjugated linoleic acids (CLA) are believed to influence body composition, blood lipids and certain endocrine parameters in animals and humans. The aim of this study was to investigate the effects of a six months dietary supplementation of 7 g CLA‐oil (containing 54% CLA) daily in two groups of male and female resistance‐trained athletes who were at a different training stage. The volunteers were matched according to their previous training: 7 beginners (3♀/4♂) and 7 advanced athletes (2♀/5♂). During the intervention period they performed a standardized training routine three times per week. Blood samples were taken and body mass index, body composition (bioelectrical impedance assessment) and nutrient intake (7‐day food record) were recorded at baseline as well as during and following dietary supplementation Results: Serum lipid concentrations, serum leptin, soluble leptin receptor and IGF‐I levels or body composition were similar in the two categories of athletes after CLA supplementation. However, despite a higher energy intake, a significant reduction of body fat (P <0.05) was observed and both groups tended to increase their body cell mass (not significant). Total body water increased in the novice athletes (P <0.05). Furthermore, total cholesterol (P = 0.049) increased over baseline levels in the novice athletes. These levels remained within the physiological range. In all athletes there was a significant correlation between percentage body fat and leptin (baseline: r² = 0.46, P = 0.01, CLA: r² = 0.49, P = 0.011), as well as between fat mass and serum leptin levels (baseline: r² = 0.35, P = 0.033, CLA: r² = 0.60, P = 0.002). Conclusions: Over a period of six months no differences were observed in the effects of a commercial CLA‐triacylglyceride (54% CLA, 7g/d) on selected endocrine parameters, blood lipids, food intake and body composition between advanced and novice resistance‐trained athletes who take part in a regular training program.     

Positional distribution of CLA in TAG of lamb tissues

The content and positional distribution of CLA in TAG fractions of lamb tissues was examined with either preformed CLA or the linoleic acid precursor of CLA in the diet as experimental treatments. The CLA content of phospholipid (PL) from these tissues was also examined. Thirteen lambs were randomized to the following dietary treatments: (i) control diet (no supplement); (ii) CLA supplementation (0.33 g d⁻¹ for 21 d prior to weaning) to milk-replacer of pre-ruminating lambs, or (iii) feeding linoleic acid-rich oil (6% safflower oil on a dry matter basis) to weaned ruminating lambs. At slaughter, tissue samples were procured from diaphragm, rib muscle, and subcutaneous (SC) adipose tissue. Safflower oil supplementation in the diet resulted in an increase in CLA content of the TAG from diaphragm, rib muscle, and SC adipose tissue by about threefold (P<0.05) on a mol% basis. CLA was localized to the sn-1/3 positions of TAG. Animals that received pre-formed CLA, however, had increased proportions of CLA at the sn-2 position of TAG from SC adipose tissue, suggesting that there were tissue-specific dietary effects and possible age-related effects on the mode of FA incorporation into TAG. Safflower oil supplementation in the diet had no effect on the CLA content of PL from diaphragm, rib muscle, and SC adipose tissue, suggesting that CLA was preferentially incorporated into the TAG of these tissues.     

<Emphasis Type="Italic">Trans</Emphasis>–<Emphasis Type="Italic">trans</Emphasis> Conjugated Linoleic Acid Enriched Soybean Oil Reduces Fatty Liver and Lowers Serum Cholesterol in Obese Zucker Rats

Conjugated linoleic acid (CLA) is a collection of octadecadienoic fatty acids that have been shown to possess numerous health benefits. The CLA used in our study was produced by the photoisomerization of soybean oil and consists of about 20% CLA; this CLA consists of 75% trans–trans (a mixture of t8,t10; t9,t11; t10,t12) isomers. This method could be readily used to increase the CLA content of all soybean oil used as a food ingredient. The objective of this study was to determine the effects of trans–trans CLA-rich soy oil, fed as a dietary supplement, on body composition, dyslipidemia, hepatic steatosis, and markers of glucose control and liver function of obese fa/fa Zucker rats. The trans–trans CLA-rich soy oil lowered the serum cholesterol and low density lipoprotein–cholesterol levels by 41 and 50%, respectively, when compared to obese controls. Trans–trans CLA-rich soy oil supplementation also lowered the liver lipid content significantly (P < 0.05) with a concomitant decrease in the liver weight in the obese rats. In addition, glycated hemoglobin values were improved in the group receiving CLA-enriched soybean oil in comparison to the obese control. PPAR-γ expression in white adipose tissue was unchanged. In conclusion, trans–trans CLA-rich soy oil was effective in lowering total liver lipids and serum cholesterol.     

Effect of conjugated FA on feed intake,body composition,and liver FA in mice

CLA is a generic term describing different isomers of linoleic acid with two conjugated double bonds. Various metabolic effects have been demonstrated following administration of CLA, including a change in body composition in animals. However, the effects of pure CLA isomers are not fully understood. In addition, conjugated octadecatrienoic acids such as calendic acid have not been extensively investigated. In this study, male and female ICR mice were fed pure CLA isomers (cis9,trans11 or trans10,cis12) or calendic acid (trans8,trans10,cis12) as their ethyl esters for 6 wk. Body protein content was significantly increased after feeding CLA isomers, either as pure isomers or as a mixture. Calendic acid significantly decreased body fat content in males. CLA (pure isomers or a mixture) significantly decreased body fat in both males and females, with the trans10,cis12 isomer being the most effective. The effect of the cis9,trans11 isomer was more pronounced in females than in males. It was concluded that the trans10,cis12 CLA isomer was mainly responsible for the decrease in fat content in mice, without a significant modification of feed efficiency, and that it was more effective than calendic acid.     

Conjugated linoleic acid and chromium lower body weight and visceral fat mass in high-fat-diet-fed mice

More than half of the U.S. population has a body mass index of 25 kg/m² or more, which classifies them as overweight or obese. Obesity is often associated with comorbidities such as diabetes, cardiovascular diseases, and cancer. CLA and chromium have emerged as major dietary supplements that reduce body weight and fat mass, and increase basal metabolic rate in animal models. However, studies show that CLA induces insulin resistance in mice and in humans, whereas Cr improves insulin sensitivity. Hence, we designed the present study to examine the combined effect of CLA and Cr on body composition and insulin sensitivity in a Balb/c mice (n=10/group) model of high-fat-diet-induced obesity. CLA alone lowered body weight, total body fat mass, and visceral fat mass, the last of which decreased further with the combination of CLA and Cr. This effect was accompanied by decreased serum leptin levels in CLA-fed and CLA+Cr-fed mice, and by higher energy expenditure (EE) and oxygen consumption (OC) in CLA+Cr-fed mice. Serum levels of glucose, insulin, the pro-inflammatory cytokines, tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6), as well as insulin resistance index (IRI), decreased with CLA, whereas CLA and Cr in combination had significant effects on insulin and IL-6 concentrations and IRI. In summary, CLA+Cr decreased body weight and fat mass in high-fat-diet-fed mice, which may be associated with decreased leptin levels and higher EE and OC.     

Dietary CLA decreased weight loss and extended survival following the onset of kidney failure in NZB/W F1 mice

In an earlier study, we showed that feeding CLA immediately after weaning prolonged survival of NZB/W F1 mice after onset of proteinuria. In the present study, the feeding of CLA was delayed until mice had developed proteinuria. Thirty NZB/W F1 mice were fed a regular rodent chow after weaning. Urine samples were collected to detect proteinuria. Once a mouse was proteinuria positive, it was then randomly assigned to a 0.5% CLA supplement semipurified diet or a control diet (supplement 0.5% corn oil). The next proteinuria positive mouse was then assigned to the opposite diet to which the first mouse was assigned. Mice fed the control diet lost 25% more body weight (13.0 g) than mice fed the CLA diet (9.7 g). Moreover, CLA-fed mice survived an average 1.7-fold longer (148 d) than mice fed the control diet (89 d) after the onset of proteinuria. This follow-up study confirmed that dietary CLA had a beneficial effect in the autoimmune NZB/W F1 mouse. In summary, the cachectic symptom of systemic lupus erythematosus was decreased by dietary CLA and survival days were increased over control group.     

Effects of trans‐10,cis‐12 and cis‐9,trans‐11 CLA on atherosclerosis in apoE/LDLR−/− mice

The objective of our studies was to verify the potential health‐related, anti‐atherogenic potency of CLA isomers, fed to apolipoprotein E and LDL receptor double knockout mice (apoE/LDLR^?/?), representing a reliable model of atherogenesis. Additionally, the effect of CLA isomers on liver steatosis was observed. In a “long experiment” (LONG), 2‐month‐old mice with no atherosclerosis were randomly assigned to three experimental groups and fed for the next 4 months. In a “short experiment” (SHORT), 4‐month‐old mice, with pre‐established atherosclerosis, were randomly assigned to three experimental groups and fed for the next 2 months. The experimental diets were: AIN‐93G (control), AIN‐93G + 0.5% trans‐10,cis‐12 CLA (t10,c12), and AIN‐93G + 0.5% cis9,trans‐11 CLA (c9,t11). In both experiments, c9,t11 CLA increased mice body weight. In mice fed t10,c12 CLA weight of liver was threefold (p<0.05) increased what was linked with hepatic steatosis observed in LONG and SHORT experiment. In LONG experiment, t10,c12 CLA significantly (p<0.05) increased plasma TAGs, whereas no such effect was observed in SHORT one. In mice receiving the CLA isomers the level of PPARα and SREBP‐1 mRNA in liver were significantly decreased. The expression of their target genes like ACO (PPARα) or FAS (SREBP‐1) were not changed. Only c9,t11 increased ACO level in LONG experiment. There were no isomer‐specific effects of CLA isomers on the area of atherosclerotic plaque. In conclusion, our results do not support the notion that CLA isomers supplementation to the diet has anti‐atherosclerotic effects. CLA isomers have no effect on atherosclerosis in apoE/LDLR^?/? mice. Practical applications: CLAs have been shown to occur naturally in food. In the last 10 years, attempts have been made to enrich animal‐derived foods in CLA isomers through animal nutrition strategies. Indeed, these attempts resulted in production of functional food such as CLA‐enriched milk (butter and cheese), ruminant and non‐ruminant meat, as well as eggs. In addition to natural foodstuff, dietary CLA supplements can also contribute to CLA intake in humans. Commercial CLA preparations, fed to laboratory animals, showed several health‐related properties, including anti‐adipogenic, anti‐carcinogenic, anti‐atherogenic, and anti‐inflammatory effects. The underlying mechanisms of action, however, are only poorly understood. The major objective of our studies was to verify the potential health‐related, namely anti‐atherogenic potency of CLA isomers, fed to apoE/LDLR^?/? mice, representing unique and reliable model of atherogenesis. Additionally, effect of CLA isomers on steatosis was observed.     

Conjugated linoleic acids: Physiological effects in animal and man with special regard to body composition

Institute of Nutrition, Friedrich Schiller University of Jena, Jena, Germany In the last decade, conjugated linoleic acids (CLA) have been shown to have some beneficial (but also unfavourable) effects: anticarcinogenic properties, immune modulation, reduction of body fat and increase of lean body mass, normalisation of impaired glucose tolerance, promotion of fatty streak formation, and isomer‐specific effects. The research base on CLA has been derived almost exclusively from animal models, while some of the biological properties have been fairly well‐documented, others are still open to question. For about 5 years a lot of commercial CLA mixtures have been offered. These mixtures produced from linoleic acid‐rich oil like sunflower or safflower oil by alkali isomerization contained, besides cis‐9,trans‐11 and trans‐10,cis‐12 CLA isomers (about 20—40% of each), parts of cis,cis and trans,trans isomers as well. The quality of the recent products is significantly improved and they contain only two CLA isomers: cis‐9,trans‐11 and trans‐10,cis‐12. CLA play apparently a key role in regulating body composition. Several studies showed a reduction in body fat mass and a slight increase in lean body mass depending on the species. A possible explanation for the decrease of body fat may be a stimulation of lipolysis and a reduction of lipoprotein lipase activity in adipocytes. In adipose and muscle tissue a CLA‐stimulated increase of carnitine palmitoyltransferase activity resulting in an enhanced fatty acid oxidation was shown. There is evidence that CLA provide protection against cytokine‐induced (Tumour necrosis factor‐α, interleukin‐1) skeletal‐muscle catabolism (anabolic effect). The body composition modulating effects are most impressive in rodents and seem to become smaller in pigs and in humans. Data on humans are insufficient. Further research is essential to characterize the multifunctionality of CLA in humans, in order to identify the specific physiological mechanism of the biologically active isomers and to determine the optimal level of these isomers for beneficial effects.     

Dietary Fat Does Not Overcome trans-10, cis-12 Conjugated Linoleic Acid Inhibition of Milk Fat Synthesis in Lactating mice

Trans-10, cis-12 conjugated linoleic acid (CLA) is a potent inhibitor of milk fat synthesis in the cow and similarly reduces milk fat in rodents. The objective of this study was to determine whether dietary fat can overcome CLA inhibition of milk fat concentration in lactating mice. Wild type C57Bl/6J mice (n = 31) were fed semipurified diets containing either low fat (LF; 4% fat) or high fat (HF; 23.6% fat) starting 4–6 days postpartum. Dietary fat was increased by inclusion of high oleic sunflower oil. After 2 days on the experimental diets, lactating dams were orally dosed with either water (control) or trans-10, cis-12 CLA (20 mg/day) for 5 days. CLA treatment decreased pup growth similarly in both HF and LF diets. Milk fat percent was increased over 16% by the HF diet and decreased over 12% by CLA, but there was no interaction of dietary fat and CLA. Both CLA and the HF diet reduced the proportion of short- and medium-chain fatty acids that originate from de novo synthesis, and there was no interaction of diet and CLA. CLA had no effect on the percent of preformed fatty acids, but the HF diet increased their abundance. Dietary fat and CLA both modified mammary expression of lipogenic enzymes and regulators, but no interactions were observed. In conclusion, CLA reduced milk fat concentration and litter growth, but these effects were not overcome by increased dietary fat from high oleic sunflower oil. CLA inhibition of milk fat in the mammary gland is not substrate dependent, and the mechanism is independent from dietary supply of oleic acid.     

Effects of dietary conjugated linoleic acid on the expression of uncoupling proteins in mice and rats

CLA inhibits mammary cancer and reduces body fat accumulation in rodents. It is not known whether uncoupling proteins (UCP), which are modulators of energy balance and metabolism, play a role in these actions of CLA. To determine the effects of dietary CLA on the expression of UCP in various tissues, 5-wk-old Sprague-Dawley rats and C57BI/6 mice were fed diets containing 1% CLA for 3 wk. CLA treatment reduced adipose depot weights in both rats and mice but had no significant effects on body weight. There was a species-specific effect of CLA on the expression of UCP. Whereas CLA did not affect the expression of UCP in most tissues in rats, mice fed CLA had increased expression of UCP2 in the mammary gland, brown adipose tissue (BAT), and white adipose tissue (WAT). Furthermore, UCP1 and UCP3 mRNA and protein levels in BAT were significantly lower in CLA-fed mice compared to controls. Skeletal muscle UCP3 mRNA was unchanged, but UCP3 protein levels were significantly increased in mice, suggesting translational or posttranslational regulation of this protein. Results from this study suggest that alterations in the expression of UCP in mice may be related to the previously reported effects of dietary CLA in lowering adiposity and increasing FA oxidation. In rats, however, induction of UCP is not likely to be responsible for fat reduction or for the inhibitory action of CLA on mammary carcinogenesis.     

Conjugated linoleic acid modulates hepatic lipid composition in mice

Conjugated linoleic acid (CLA) is a chemoprotective fatty acid that inhibits mammary, colon, forestomach, and skin carcinogenesis in experimental animals. We hypothesize that the ubiquitous chemoprotective actions of dietary CLA in extrahepatic tissues are dependent upon its role in modulating fatty acid composition and metabolism in liver, the major organ for lipid metabolism. This study begins to evaluate the role of CLA in lipid metabolism by determining the modulation of fatty acid composition by CLA. Female SENCAR mice were fed semipurified diets containing 0.0% (Diet A), 0.5% (Diet B), 1.0% (Diet C), or 1.5% (Diet D) CLA (by weight) for six weeks. Mice fed Diets B, C, and D exhibited lower body weights and elevated amounts of extractable total lipid in livers compared with mice fed diets without CLA (Diet A). Analyses of the fatty acid composition of liver by gas chromatography revealed that dietary CLA was incorporated into neutral and phospholipids at the expense of linoleate in Diets B, C, and D; oleate increased and arachidonate decreased in neutral lipids of CLA diet groups. In addition, increasing dietary CLA was associated with reduced linoleate in hepatic phospholipids. In an in vitro assay, CLA was desaturated to an unidentified 18:3 product to a similar extent as linoleate conversion to γ-linolenate (9.88, and 13.63%, respectively). These data suggest that CLA may affect metabolic interconversion of fatty acids in liver that may ultimately result in modified fatty acid composition and arachidonate-derived eicosanoid production in extrahepatic tissues. In addition to determining how dietary CLA modulates eicosanoid synthesis, further work is needed to identify enzymatic products that may result from desaturation of CLA.     

Analytical techniques for conjugated linoleic acid (CLA) analysis

Interest in conjugated linoleic acid (CLA) research has increased significantly in recent years because various CLA isomers have been reported to exhibit different beneficial physiological effects in laboratory animals. These findings are detailed in the first book on this subject entitled Advances in CLA Research, Volume 1, edited by M. P. Yurawecz, M. M. Mossoba, J. K. G. Kramer, M. W. Pariza, and G. J. Nelson, and published by the American Oil Chemists Society, Champaign, Illinois, USA, in 1999. Various mixtures of CLA isomers are sold as dietary supplements today, but the biological activities observed in animal models have yet to be demonstrated in humans. Hurdles to achieving this goal include the commercial unavailability of many individual CLA isomers, and the challenge of isolating, separating and confirming the identity of low levels of CLA isomers and their metabolites in complex chemical and/or biological matrices. Therefore, there has been a critical need for analytical methodologies that can meet these difficult objectives. This dossier is about a collection of useful analytical techniques and procedures some of which are well known, while others have only recently been developed and successfully applied to CLA research. These include GC, Ag⁺‐HPLC, RP‐HPLC, GC‐MS, GC‐IR, and NMR.     

Impact of Conjugated Linoleic Acid (CLA) on Skeletal Muscle Metabolism

Conjugated linoleic acid (CLA) has garnered special attention as a food bioactive compound that prevents and attenuates obesity. Although most studies on the effects of CLA on obesity have focused on the reduction of body fat, a number of studies have demonstrated that CLA also increases lean body mass and enhances physical performances. It has been suggested that these effects may be due in part to physiological changes in the skeletal muscle, such as changes in the muscle fiber type transformation, alteration of the intracellular signaling pathways in muscle metabolism, or energy metabolism. However, the mode of action for CLA in muscle metabolism is not completely understood. The purpose of this review is to summarize the current knowledge of the effects of CLA on skeletal muscle metabolism. Given that CLA not only reduces body fat, but also improves lean mass, there is great potential for the use of CLA to improve muscle metabolism, which would have a significant health impact.     

Effect of conjugated linoleic acid on body composition in mice

The effects of conjugated linoleic acid (CLA) on body composition were investigated. ICR mice were fed a control diet containing 5.5% corn oil or a CLA-supplemented diet (5.0% corn oil plus 0.5% CLA). Mice fed CLA-supplemented diet exhibited 57% and 60% lower body fat and 5% and 14% increased lean body mass relative to controls (P<0.05). Total carnitine palmitoyltransferase activity was increased by dietary CLA supplementation in both fat pad and skeletal muscle; the differences were significant for fat pad of fed mice and skeletal muscle of fasted mice. In cultured 3T3-L1 adipocytes CLA treatment (1×10⁻⁴ M) significantly reduced heparin-releasable lipoprotein lipase activity (−66%) and the intracellular concentrations of triacylglyceride (−8%) and glycerol (−15%), but significantly increased free glycerol in the culture medium (+22%) compared to control (P<0.05). The effects of CLA on body composition appear to be due in part to reduced fat deposition and increased lipolysis in adipocytes, possibly coupled with enhanced fatty acid oxidation in both muscle cells and adipocytes.     

Effects of dietary conjugated linoleic acids on hepatic and muscle lipids in hybrid striped bass

Conjugated linoleic acids (CLA) are the focus of numerous studies, yet the effects of these isomers of octadecadienoic acids have not been evaluated in many species of fish. In this study, graded amounts of CLA-0,0.5, 0.75, or 1.0% of the diet—were fed to juvenile hybrid striped bass for 8 wk. Dietary treatments were fed to apparent satiation twice daily to triplicate groups of fish initially weighing 13.4 g/fish. Feed intake and weight gain of fish fed 1.0% CLA were significantly reduced compared to fish fed no CLA. Fish fed 0.5 and 0.75% CLA exhibited reduced feed intake similar to fish fed 1.0% CLA, but had growth rates that were not significantly different from those of fish fed no CLA. Feed efficiency improved significantly in fish as dietary CLA concentrations increased. Total liver lipid concentrations were significantly reduced in fish fed the diets containing CLA compared to those of fish fed the control diet, and intraperitoneal fat ratio was significantly lower in fish fed 1.0% CLA compared to fish fed no CLA. Fish fed dietary CLA exhibited significant increases in hepatosomatic index and moisture content of muscle and carcass. The CLA isomers were detected in liver and muscle of fish fed the diets containing CLA, while a low concentration of one isomer was detected in liver and muscle of fish fed the control diet. Dietary CLA resulted in a significant increase in 18∶2(c-9,c-12) concentration in liver and muscle, but a significant reduction in 18∶1n−7 in these tissues. Furthermore, feeding CLA resulted in a significant increase in the concentration of 20∶5n−3 and 22∶6n−3 in liver, but a reduction of these fatty acids in muscle. This study showed that feeding CLA elevated tissue concentrations of these fatty acid isomers, reduced tissue lipid contents, improved feed efficiency, and altered fatty acid concentrations in liver and muscle of fish.     

Dietary CLA Combined with Palm Oil or Ovine Fat Differentially Influences Fatty Acid Deposition in Tissues of Obese Zucker Rats

The effect of dietary conjugated linoleic acid (CLA) supplementation in combination with fat from vegetable versus animal origin on the fatty acid deposition, including that of individual 18:1 and 18:2 (conjugated and non-conjugated) isomers, in the liver and muscle of obese rats was investigated. For this purpose, 32 male Zucker rats were randomly assigned to one of four diets containing palm oil or ovine fat, supplemented or not with 1% of 1:1 cis(c)9,trans(t)11 and t10,c12 CLA isomers mixture. Total fatty acid content decreased in the liver and muscle of CLA-fed rats. In the liver, CLA increased saturated fatty acids (SFA) in 11.9% and decreased monounsaturated fatty acids (MUFA) in 6.5%. n-3 Polyunsaturated fatty acids (PUFA) relative proportions were increased in 30.6% by CLA when supplemented to the ovine fat diet. In the muscle, CLA did not affect SFA but decreased MUFA and PUFA percentages. The estimation of Δ9-indices 16 and 18 suggested that CLA inhibited the stearoyl-CoA desaturase activity in the liver (a decrease of 13–38%), in particular when supplemented to the ovine fat diet. Concerning CLA supplementation, the t10,c12 isomer percentage was 60–80% higher in the muscle than in the liver. It is of relevance that rats fed ovine fat, containing bio-formed CLA, had more c9,t11 CLA isomer deposited in both tissues than rats fed palm oil plus synthetic CLA. These results highlight the importance to further clarify the biological effects of consuming foods naturally enriched in CLA, alternatively to CLA dietary supplementation.