Efficacy and safety of dietary supplements containing CLA for the treatment of obesity: evidence from animal and human studies

Dietary conjugated linoleic acids decrease leptin in porcine adipose tissue

We investigated the effects of dietary conjugated linoleic acids (CLA) on white adipose tissue (WAT) in heavy pigs. Twelve pigs were assigned to 1 of 2 groups supplemented with either 0 or 0.75% of a CLA preparation (isomeric mixture) and were slaughtered at 159 +/- 2.3 kg live weight. Their subcutaneous WAT was analyzed by both chemical and microanatomical methods. The WAT of CLA-fed pigs tended to have a higher protein content (P = 0.064) and smaller adipocytes (P = 0.053) than that of control (CTR) pigs. The number of proliferating preadipocytes tended to be greater (P = 0.076) in pigs fed CLA, whereas the number of apoptotic adipocytes was greater (P < 0.01) than in CTR pig. Immunohistochemistry revealed that leptin (Ob) expression was lower (P = 0.048) in adipocytes from treated pigs and Western blot quantification of Ob revealed lower levels (P < 0.05) in CLA-fed pigs. The Ob receptor was not affected by dietary CLA supplementation. Tyrosine hydroxylase activity was higher (P < 0.001) in WAT of CLA fed-pigs than in CTR. It is conceivable that the increased noradrenergic activity due to dietary CLA decreases the Ob expression, although it does not diminish the lipid content of WAT, at least in heavy pigs. This article describes the interaction between CLA and Ob in the WAT of heavy pigs and we hypothesize that there is an increased noradrenergic stimulation of lipolysis directly in the target tissue.

Efeito da suplementação com ácido linoléico conjugado e do treinamento em natação sobre a composição corporal e os parâmetros bioquímicos de ratos Wistar em crescimento

OBJETIVO: Avaliar os efeitos da suplementação com ácido linoléico conjugado, associada ao treinamento moderado em natação, sobre a composição corporal, o consumo e a eficiência alimentar, a glicemia, o perfil lipídico e o glicogênio muscular e hepático de ratos Wistar. MÉTODOS: Ratos Wistar (30 dias) foram divididos em: sedentário, sedentário suplementado, treinado e treinado suplementado. Permaneceram em gaiolas individuais com comida e água ad libitum, temperatura de 23ºC (com variação de1ºC) e ciclo claro-escuro de 12 horas, durante 8 semanas. A sessão de natação durou 1 hora e foi realizada três vezes/semana, bem como a suplementação com ácido linoléico conjugado a 2%. Após sacrifício, o plasma, os tecidos adiposos brancos e o marrom, o músculo gastrocnêmio e o fígado foram coletados e pesados. RESULTADOS: A suplementação per se não promoveu modificação na ingestão alimentar e na massa corporal dos animais. Houve aumento na glicemia de jejum (p<0,05), nas lipoproteínas de alta densidade (p<0,05), no colesterol total (p<0,05) e redução dos triacilgliceróis. A suplementação associada ao treinamento reduziu a massa corporal (p<0,05) e aumentou o peso relativo do tecido adiposo, do fígado e a glicemia de jejum. CONCLUSÃO: A suplementação com ácido linoléico conjugado associada à prática de exercício físico parece ter influência no balanço energético, mas, por outro lado, o aumento no peso do fígado indica que a ingestão deste ácido graxo pode ter efeitos indesejáveis, aumentando as chances de desenvolvimento do fígado gorduroso. Estes achados apontam perspectivas para novos estudos envolvendo análises histológicas do fígado, expressão gênica de enzimas chaves do metabolismo lipídico e de carboidratos, associados ou não a diferentes protocolos de treinamento físico.

Weak effect of trans-10, cis-12-conjugated linoleic acid on body fat accumulation in adult hamsters

It has been proposed that young animals and subjects are more responsive to conjugated linoleic acid (CLA) than the adults. Nevertheless, there is very little information concerning the effectiveness of CLA in adult animals. In the present study we aimed to explore the effects of trans-10, cis-12-CLA on body fat accumulation in adult hamsters, as well as on some of the molecular mechanisms described in young animals as responsible for the CLA body fat-lowering effect, such as lipogenesis, lipoprotein lipase (LPL)-mediated fat uptake and thermogenesis. The experiment was conducted with sixteen adult male Syrian Golden hamsters (aged 8 months) fed a high-fat diet supplemented or not with 0.5 % trans-10, cis-12-CLA for 6 weeks. Acetyl-CoA carboxylase (ACX), fatty acid synthase (FAS), LPL, PPARgamma, sterol regulatory element-binding protein (SREBP)-1a and SREBP-1c expressions were assessed in subcutaneous and perirenal adipose tissues by real-time RT-PCR. Total and heparin-releasable LPL activities were determined in subcutaneous adipose tissue by fluorimetry and FAS activity by spectrophotometry. Uncoupling protein-1 (UCP1) expression in interscapular brown adipose tissue was assessed by Western blot. Hamsters fed the trans-10, cis-12-CLA diet showed a significant reduction in subcutaneous adipose tissue. No changes were observed in the expression of ACX, FAS, LPL, SREBP-1a, SREBP-1c and PPARgamma, nor in total and heparin-releasable LPL and FAS activities. Trans-10, cis-12-CLA induced a significant increase in the amount of UCP1. These results suggest a low responsiveness to trans-10, cis-12-CLA in adults, lower than that in young hamsters. One of the reasons explaining this difference is the lack of effect on LPL.

Pursuit of oxidation behavior for conjugated polyenoyl glycerols and establishment of their novel oxidation prevention method

Although conjugated oils are paid much attentions to their interesting physiological properties such as anticancer, anti-arteriosclerosis, anti-hypertension activities, loss in body fat etc, there is few information on their oxidation behavior. In the present work, their oxidation behavior and oxidation prevention method were evaluated to utilize as functional foods or drugs. As results, an oxidation behavior of conjugated oils was different from that of corresponding non-conjugated oils, and conjugated oils were supposed to form not only hydroperoxides but also kinds of cyclic peroxides as primary oxidation products in the autoxidation. In a thermal oxidation, polymerization reaction might be prior to decomposition reaction owing to form a large quantity of more polymerized products in conjugated oils. Solidification of conjugated oils by thermal oxidation was prevented for long time by addition of tocopherol, and optimal addition amounts of tocopherol into conjugated oils were 1,000 ppm either in autoxidation or thermal oxidation. Equi-molar of phosphatidyl ethanolamine showed synergistic effect slightly on 1,000 ppm tocopherol for preventing thermal oxidation of conjugated oil.

Effect of CLA isomers and their mixture on aging C57Bl/6J mice

BACKGROUND

Dietary supplements containing conjugated linoleic acid (CLA) are widely promoted for weight loss management over the counter. Recently, FDA approved the CLA as Generally Recognized as Safe category so that it can be used in various food and beverages. The combined effect of CLA isomers have been studied extensively in animals and humans, however, the role of individual isomers remains unraveled.

AIM

The present investigation addresses the effects of CLA isomers on body composition and body weight as well as safety using female C57Bl/6J aging mice.

METHODS

Two main CLA isomers and their mixture were fed to 12-months-old female C57Bl/6J mice. Ten percent corn oil (CO) based fat diet supplemented with 0.5% purified cis 9 trans 11 (c9,t11) CLA or trans 10 cis 12 (t10,c12) CLA or their mixture (CLA mix, 50:50) for 6 months. The lean mass, fat mass, glucose, non-esterified fatty acids, and insulin were examined at the end of study.

RESULTS

As a result of 6 months dietary intervention, both t10,c12 CLA and CLA mix groups showed increased lean mass and reduced fat mass compared to that of c9,t11 CLA and CO group. However, insulin resistance and liver hypertrophy were observed in t10,c12 CLA and CLA mix groups based on the results of homeostasis model assessment, revised quantitative insulin-sensitivity check index (R-QUICKI), intravenous glucose tolerance test, and liver histology. Liver histology revealed that increased liver weight was due to hypertrophy.

CONCLUSION

In conclusion, the major CLA isomers have a distinct effect on fat mass, glucose, and insulin metabolism. The t10,c12 isomer was found to reduce the fat mass and to increase the lean mass but significantly contributed to increase insulin resistance and liver hypertrophy, whereas c9,t11 isomer prevented the insulin resistance. Between the two major CLA isomers, the t10,c12 was attributed to reduce fat mass whereas, c9,t11 improves the insulin sensitivity.

Diet supplementation with the cis-9,trans-11 conjugated linoleic acid isomer affects the size of adipocytes in Wistar rats

Previous reports have demonstrated that conjugated linoleic acid (CLA) acts on body fat accumulation in a variety of animal models. The aim of the present study was to investigate the effect of cis (c)-9,trans (t)-11 and t10,c12 CLA isomers on the number and size of adipocytes from the inguinal and retroperitoneal fats in Wistar male rats. A 5.1% palm oil-based diet was supplemented with CLA isomers as follows: 0.6% of c9,t11, 0.6% of t10,c12, 1.3% of c9,t11 and t10,c12 isomers in mixture, and a control nonsupplemented group for comparative purposes. Fat tissues were prepared on microscope slides for histologic examination using an image-analysis software to count the number of adipocytes and measure cell sizes. The results showed that CLA isomers did not affect (P > .05) either final body and fat depot weights or serum lipids (with the exception of triacylglycerols) and adipocytokines (leptin and adiponectin). Animals fed the c9,t11 CLA isomer diet showed larger adipocytes when compared to other groups. Independently of the CLA dietary treatment, retroperitoneal fat showed larger adipocytes (3319 microm(2)) and therefore a smaller number of adipocytes per unit of area, compared to inguinal fat (3055 microm(2)). Taken together, the data suggest that a palm oil-based diet supplemented with the c9,t11 CLA isomer in Wistar rats, in contrast to the t10,c12 isomer and the mixture of both isomers, increases adipocyte dimensions in inguinal and retroperitoneal fat depots, while having a minor effect in serum lipids and adipocytokines.

Dairy product consumption and the metabolic syndrome

The metabolic syndrome is an important risk factor for type 2 diabetes mellitus and CVD. Epidemiological studies have now suggested protective effects of dairy product consumption on the development of this syndrome. Here we review the physiological effects and possible mechanisms involved of three main dairy constituents (Ca, protein, fat) on important components of the metabolic syndrome. Ca supplements improve the serum lipoprotein profile, particularly by decreasing serum total and LDL-cholesterol concentrations. They also lower systolic and diastolic blood pressure. Insufficient evidence exists for a significant role of Ca supplements or dairy in body-weight management. Effects of Ca may be related to intestinal binding to fatty acids or bile acids, or to changes in intracellular Ca metabolism by suppressing calciotropic hormones. Dietary proteins may increase satiety in both the short and longer term, which may result in a reduced energy intake. They have also been reported to improve the serum lipoprotein profile as compared with carbohydrates. Dairy proteins are precursors of angiotensin-I-converting enzyme-inhibitory peptides, which may lower blood pressure. Such effects, however, have inconsistently been reported in human studies. Finally, conjugated linoleic acid, which effectively lowers body weight in animals, has no such effect in humans in the quantities provided by dairy products. To reduce the intake of SFA, the consumption of low-fat instead of high-fat dairy products is recommended. In conclusion, more research is warranted to better understand the physiological effects and the mechanisms involved of dairy products in the prevention and treatment of the metabolic syndrome.

Adiposity and serum parameters in hamsters fed energy restricted diets supplemented or not with trans-10,cis-12 conjugated linoleic acid

Numerous studies have demonstrated that conjugated linoleic acid (CLA) modulates body composition, reducing body fat accumulation in various mammalian species. However, very few studies have been carried out to assess the effect of CLA on previously stored body fat. The aim of the present work was to analyse the effectiveness of trans-10,cis-12 CLA in improving alterations produced by high-fat feeding in body fat and serum parameters when it was included in an energy-restricted diet. For this purpose male Syrian Golden hamsters were fed on high-fat diet for 7 weeks in order to increase their body fat content, and a further 25% energy-restricted diet supplemented or not with 0.5% trans-10,cis-12 CLA for 3 weeks. Adipose tissues, liver and gastrocnemious muscles were dissected and weighed. Adipocyte diameter and number were assessed in epididymal adipose tissue. Total cholesterol, triacylglycerols, non-esterified fatty acids and glucose were measured in serum. Three weeks of energy restriction resulted in a reduction in body weight and white adipose tissue size in all anatomical locations, without changes in liver and gastrocnemious muscle weights. Epididymal adipocyte size was reduced, but total adipocyte number remained unchanged. Serum cholesterol, triacylglycerols and glucose were significantly reduced. No differences were observed between the restricted groups (control and CLA supplemented). In conclusion, under our experimental conditions, the addition of trans-10,cis-12 CLA to the diet does not increase the benefits produced by energy restriction.

Conjugated linoleic acids differentially alter polyp number and diameter in the Apc(min/+) mouse model of intestinal cancer

OBJECTIVE

Dietary conjugated linoleic acids (CLA) have had many health benefits claimed for them, including antineoplastic actions.

MATERIALS AND METHODS

The effects of the predominant forms of CLA, namely the c9t11 and t10c12 isomers, or a mixture of these on polyp development, were investigated in the Apc(Min/+) mouse. CLAs have also been linked to altered rates of cell renewal and cell proliferation so this was also studied, as was a further means of increasing tissue mass, namely crypt fission.

RESULTS

The stomach and small intestine were significantly heavier in the t10c12, and in the mixture-treated groups (P < 0.001). Crypt fission was increased in the middle small intestine by the t10c12 diet while colonic weight was reduced by c9t11 provision and crypts were 20% shorter. The t10c12 and the mixture significantly reduced polyp number in the proximal small intestine but they increased polyp diameter in the middle and distal small intestine, to an extent that the polyp burden was significantly increased at these sites. All CLAs significantly reduced polyp number in the colon, but the mixture significantly increased polyp diameter in the colon.

CONCLUSION

Increased polyp diameter associated with t10c12 diet and especially with the mixture is a cause of concern, as this is the commercially available form. The naturally occurring isomer, c9t11 decreased colonic polyp number and did not increase diameter, suggesting that this natural isomer is the most likely to be protective.

Effects of conjugated linoleic acid plus n-3 polyunsaturated fatty acids on insulin secretion and estimated insulin sensitivity in men

BACKGROUND/OBJECTIVES

Dietary addition of either conjugated linoleic acid (CLA) or n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFAs) has been shown to alter adiposity and circulating lipids, risk markers of cardiovascular diseases. However, CLA may decrease insulin sensitivity, an effect that may be reversed by n-3 LC-PUFA. Thus, the potential of CLA plus n-3 LC-PUFA to affect insulin secretion and sensitivity in non-diabetic young and old, lean and obese subjects was tested.

SUBJECTS/METHODS

CLA (3 g daily) plus n-3 LC-PUFA (3 g daily) or control oil (6 g daily) was given to lean (n=12; BMI 20-26 kg/m(2)) or obese (n=10; BMI 29-35 kg/m(2)) young (20-37 years old) or lean (n=16) or obese (n=11) older men (50-65 years) for 12 weeks. The study had a double-blind, placebo-controlled randomized crossover design, and primary end points were insulin secretion and sensitivity during a standardized meal test, evaluated by modeling glucose, insulin and C-peptide data.

RESULTS

The combination was well tolerated. There was no significant difference in fasting levels of glucose, insulin or C-peptide after CLA/n-3 LC-PUFA treatment compared with control oil. Neither insulin secretion nor estimated sensitivity was affected by CLA/n-3 LC-PUFA in lean or obese young subjects or in older lean subjects. However, in older obese subjects, estimated insulin sensitivity was reduced with CLA/n-3 LC-PUFA compared with control (P=0.024).

CONCLUSIONS

The results do not support beneficial effects of CLA/n-3 LC-PUFA for beta-cell dysfunction or insulin resistance in humans but suggest that insulin sensitivity in older obese subjects is reduced.

Trans-10, cis-12 conjugated linoleic acid antagonizes ligand-dependent PPARgamma activity in primary cultures of human adipocytes

We previously demonstrated that trans-10, cis-12 (10,12) conjugated linoleic acid (CLA) causes human adipocyte delipidation, insulin resistance, and inflammation in part by attenuating PPARgamma target gene expression. We hypothesized that CLA antagonizes the activity of PPARgamma in an isomer-specific manner. 10,12 CLA, but not cis-9, trans-11 (9,11) CLA, suppressed ligand-stimulated activation of a peroxisome proliferator response element-luciferase reporter. This decreased activation of PPARgamma by 10,12 CLA was accompanied by an increase in PPARgamma and extracellular signal-related kinase (ERK)1/2 phosphorylation, followed by decreased PPARgamma protein levels. To investigate if 10,12 CLA-mediated delipidation was preventable with a PPARgamma ligand (BRL), cultures were treated for 1 wk with 10,12 CLA or 10,12 CLA + BRL and adipogenic gene and protein expression, glucose uptake, and triglyceride (TG) were measured. BRL cosupplementation completely prevented 10,12 CLA suppression of adipocyte fatty acid-binding protein, lipoprotein lipase, and perilipin mRNA levels without preventing reductions in PPARgamma or insulin-dependent glucose transporter 4 (GLUT4) expression, glucose uptake, or TG. Lastly, we investigated the impact of CLA withdrawal in the absence or presence of BRL for 2 wk. CLA withdrawal did not rescue CLA-mediated reductions in adipogenic gene and protein expression. In contrast, BRL supplementation for 2 wk following CLA withdrawal rescued mRNA levels of PPARgamma target genes. However, the levels of PPARgamma and GLUT4 protein and TG were only partially rescued by BRL. Collectively, we demonstrate for the first time, to our knowledge, that 10,12 CLA antagonizes ligand-dependent PPARgamma activity, possibly via PPARgamma phosphorylation by ERK.

Evaluating the conjugated linoleic acid and trans 18:1 isomers in milk fat of dairy cows fed increasing amounts of sunflower oil and a constant level of fish oil

The objective was to evaluate different levels of sun-flower oil (SFO) in dairy rations to increase vaccenic (trans-11-18:1) and rumenic acids (cis-9,trans-11-18:2) in milk fat, and assess the content and composition of other trans-octadecenoic (trans-18:1) and conjugated linoleic acids (CLA) isomers. Eighty lactating Holstein cows were fed control diets for 4 wk and then placed on 4 diets for 38 d; milk fat was analyzed after 10 and 38 d. The treatments were: control, 1.5% SFO plus 0.5% fish oil (FO), 3% SFO plus 0.5% FO, and 4.5% SFO plus 0.5% FO. The forage-to-concentrate ratio was 50:50 and consisted of barley/alfalfa/hay silage and corn/barley grain concentrate. There were no differences in milk production. Supplementation of SFO/FO reduced milk fat compared with respective pretreatment periods, but milk protein and lactose levels were not affected. There was a linear decrease in all short- and medium-chain saturated fatty acids (SFA) in milk fat after 10 d (25.5, 24.1, 20.2, and 16.7%) and a corresponding linear increase in total trans-18:1 (5.2, 9.1, 14.1, and 21.3%) and total CLA (0.7, 1.9, 2.4, and 3.9%). The other FA in milk fat were not affected. Separation of trans-18:1 isomers was achieved by combination of gas chromatography (GC; 100-m highly polar capillary column) and prior separation of trans FA by silver ion-thin layer chromatography followed by GC. The CLA isomers were resolved by a combination of GC and silver ion-HPLC. The trans-11- and trans-10-18:1 isomers accounted for approximately 50% of the total trans-18:1 increase when SFO/FO diets were fed. On continued feeding to 38 d, trans-11-18:1 increased with 1.5% SFO/FO, stayed the same with 3%, and declined with 4.5% SFO/FO. Rumenic acid showed a similar pattern on continued feeding as trans-11-18:2; levels increased to 0.43, 1.5, 1.9, and 3.4% at 10 d and to 0.42, 2.15, 2.09, and 2.78% at 38 d. Rumenic acid was the major CLA isomer in all 4 diets: 66, 77, 78 and 85%. The CLA isomers trans-7,cis-9-, trans-9,cis-11-, trans-10,cis-12-, trans-11,trans-13-, and trans-9,trans-11-/trans-10,trans-12-18:2 also increased from 0.18 (control) to 0.52% (4.5% SFO/FO). Milk fat produced from 3% SFO/FO appeared most promising: trans-11-18:1 and cis-9,trans-11-18:2 increased 4.5-fold, total SFA reduced 18%, and moderate levels of trans-10-18:1 (3.2%), other trans-18:1 (6.6%) and CLA isomers (0.5%) were observed, and that composition remained unchanged to 38 d. The 4.5% SFO/FO diet produced higher levels of trans-11-18:1 and cis-9,trans-11-18:2, a 28% reduction in SFA, and similar levels of other trans-18:1 (9.2%) and CLA isomers (0.52%), but the higher levels of trans-11-18:1 and cis-9,trans-11-18:2 were not sustained. A stable milk fat quality was achieved by feeding moderate amounts of SFO (3% of DM) in the presence of 0.5% FO that had 4% vaccenic and 2% rumenic acids.

Effects of margarine and butter consumption on distribution of trans-18:1 fatty acid isomers and conjugated linoleic acid in major serum lipid classes in lactating women

Trans FA (TFA) have at least one trans double bond and comprise several isomers and types, including many of the CLA (e.g., c9,t11-18:2 CLA). Some TFA may have adverse effects (e.g., cardiovascular disease), whereas some are thought to have beneficial effects (e.g., anticarcinogenicity). The presence of TFA in human tissues and fluids is related to dietary intake, although this relationship is not completely understood--especially in regard to serum lipid fractions. This study was conducted as part of an investigation designed to test the influence of butter (B), "low TFA" margarine (LT), and regular margarine (RM) on milk fat content. Here we tested the secondary hypothesis that consumption of B, LT, and RM by lactating women would result in differential distribution of TFA and CLA in major serum lipid classes. Breast-feeding women (n = 11) participated in this randomized Latin-square study consisting of five periods: intervention I (5 d), washout I (7 d), intervention II (5 d), washout II (7 d), and intervention III (5 d). Extracted serum lipid was separated into cholesterol ester (CE), TAG, and phospholipid (PL) fractions and analyzed for total and isomeric TFA and CLA concentrations. Data indicate that TAG consistently contained the highest concentration of total t-18:1. No interaction between treatment and fraction was found for any of the t-18:1 isomers identified. Absolute concentration of each t-18:1 isomer was greatest during the RM period, regardless of fraction. On a relative basis, concentrations of t10-18:1 and t12-18:1 were most responsive to treatment in the CE fraction. The concentration of c9,t11-18:2 CLA was highest in the TAG fraction and lowest in the PL fraction, regardless of treatment. In summary, these results indicate (i) that there is a differential distribution of some isomeric TFA and CLA among human serum lipid fractions and (ii) that dietary TFA intake influences absolute and relative concentrations of some of the isomers in selected fractions.

Effects of three different conjugated linoleic acid preparations on insulin signalling, fat oxidation and mitochondrial function in rats fed a high-fat diet

To investigate the effects of three different conjugated linoleic acid (CLA) preparations containing different ratios of CLA isomers on insulin signalling, fatty acid oxidation and mitochondrial function, Sprague–Dawley rats were fed a high-fat diet either unsupplemented or supplemented with one of three CLA preparations at 1 % of the diet for 8 weeks. The first CLA preparation contained approximately 30 %cis-9,trans-11 (c9,t11)-CLA isomer and 40 %trans-10,cis-12 (t10,c12)-CLA isomer (CLA-mix). The other two preparations were an 80:20 mix (c9,t11-CLA-mix) or a 10:90 mix of two CLA isomers (t10,c12-CLA-mix). Insulin resistance was decreased in all three supplemented groups based on the results of homeostasis model assessment and the revised quantitative insulin-sensitivity check index. The phosphorylation of insulin receptor substrate-1 on serine decreased in the livers of all three supplemented groups, while subsequent Akt phosphorylation increased only in thet10,c12-CLA-mix group. Both thec9,t11-CLA-mix and thet10,c12-CLA-mix increased the expression of hepatic adiponectin receptors R1 and 2, which are thought to enhance insulin sensitivity and fat oxidation. Thec9,t11-CLA-mix increased protein and mRNA levels of PPARα, acyl-CoA oxidase and uncoupling protein, which are involved in fatty acid oxidation and energy dissipation. Thec9,t11-CLA-mix enhanced mitochondrial function and protection against oxidative stress by increasing the activities of cytochromecoxidase, manganese-superoxide dismutase, glutathione peroxidase, and glutathione reductase and the level of GSH. In conclusion, all three CLA preparations reduced insulin resistance. Among them, thec9,t11-CLA-mix was the most effective based on the parameters reflecting insulin resistance and fat oxidation, and mitochondrial antioxidative enzyme activity in the liver.

Chromium picolinate and conjugated linoleic acid do not synergistically influence diet- and exercise-induced changes in body composition and health indexes in overweight women

This study assessed the effects of combined chromium picolinate (CP) and conjugated linoleic acid (CLA) supplementation on energy restriction and exercise-induced changes in body composition, glucose metabolism, lipid lipoprotein profile and blood pressure in overweight, premenopausal women. For 12 weeks, 35 women [age 36+/-1 years (mean+/-S.E.M.); BMI 28.0+/-0.5 kg/m2] were counseled to consume a 2092 kJ/day (500 kcal/day) energy deficit diet and performed 30 min of moderate-intensity walking or jogging 5 days/week. The women were randomly assigned to ingest either CP-CLA [400 mug chromium (Cr), 1.8 g CLA in 2.4 g tonalin oil, n=19] or placebo (<0.1 microg Cr, 2.4 g canola oil, n=16). Compared to baseline, urinary Cr excretion increased 22-fold, plasma CLA isomer 18:2 (c9,t11) content increased 79% and plasma CLA isomer 18:2 (t10,c12) became detectable in CP-CLA and were unchanged in Placebo. Over time, body weight decreased 3.5+/-0.5% (CP-CLA -2.6+/-0.5; placebo -2.5+/-0.5 kg) and fat mass decreased 8.9+/-1.3% (CP-CLA -2.7+/-0.5, placebo -2.4+/-0.5 kg), with no differences in responses between groups. Fasting blood hemoglobin A1c, plasma glucose and insulin, a homeostatic assessment of insulin resistance, serum total cholesterol (CHOL), high-density lipoprotein cholesterol (HDL), low-density lipoprotein cholesterol, triacylglycerol (TG), CHOL/HDL ratio, TG/HDL ratio and sitting systolic and diastolic blood pressures were not changed over time or influenced by CP-CLA. The use of a combined CP and CLA supplement for 3 months does not affect diet- and exercise-induced changes in weight and body composition or improve indexes of metabolic and cardiovascular health in young overweight women.

Comparing subcutaneous adipose tissue in beef and muskox with emphasis on trans 18:1 and conjugated linoleic acids

Muskox (Ovibos moschatus) are ruminant animals native to the far north and little is known about their fatty acid composition. Subcutaneous adipose tissue (backfat) from 16 wild muskox was analyzed and compared to backfat from 16 barley fed beef cattle. Muskox backfat composition differed substantially from beef and the most striking difference was a high content of 18:0 (26.8 vs. 9.77%). This was accompanied by higher levels of most other saturated fatty acids except beef had more 16:0. Muskox backfat also had a lower level of cis-18:1 and this was related to a lower expression of steroyl-CoA desaturase mRNA. Beef backfat had a higher level of total trans-18:1 (4.25 vs. 2.67%). The most prominent trans-18:1 isomers in beef backfat were 10t-18:1 (2.13%) and 11t-18:1 (0.77%) whereas the most prominent isomers in muskox backfat were 11t-18:1 (1.41%), 13t/14t- (0.27%) and 16t-18:1 (0.23%). The total conjugated linoleic acid (CLA) content was higher in beef backfat than muskox (0.67 vs. 0.50%) with 9c,11t-18:2 as the most abundant CLA isomer. The second most abundant CLA isomer in beef backfat was 7t,9c-18:2 (0.10%) whereas in muskox it was 11t13c-18:2 (0.04%). Muskox backfat had a higher content of 18:3n-3 and its elongation and desaturation products 20:5n-3, 22:5n-3 and 22:6n-3 and a lower n-6/n-3 ratio. Overall, the high forage diet of muskox seemed to produce a healthier fatty acid profile and highlighted the need to develop feeding strategies for intensively raising beef that will not negatively impacting fatty acid composition.

The effects of conjugated linoleic acid on human health-related outcomes

Conjugated linoleic acid (CLA) is a collective term for a mixture of positional and geometric isomers of conjugated dienoic derivatives of linoleic acid. CLA has received considerable attention as a result of animal experiments that report anti-carcinogenic, anti-atherogenic and anti-diabetic properties, and modulation of body composition and immune function. Several studies of CLA supplementation in human subjects have now been published, but in contrast to animal studies there has been marked variation between reports on the health-related outcomes. The consensus from seventeen published studies in human subjects is that CLA does not affect body weight or body composition. Some detrimental effects of thetrans-10,cis-12 CLA isomer have also been reported in terms of altered blood lipid composition and impaired insulin sensitivity. Finally, CLA has only limited effects on immune functions in man. However, there have been reports of some interesting isomer-specific effects of CLA on the blood lipid profile, but not on immune function. These isomer-specific effects need further investigation. Until more is known, CLA supplementation in man should be considered with caution.

Conjugated eicosapentaenoic acid inhibits vascular endothelial growth factor-induced angiogenesis by suppressing the migration of human umbilical vein endothelial cells

We have previously shown that conjugated eicosapentaenoic acid (CEPA), which is prepared by alkaline treatment of eicosapentaenoic acid and contains conjugated double bonds, suppresses tumor growth in vivo. In this earlier study, blood vessels were observed on the tumor surface in control mice, whereas in CEPA-treated mice, no such vessels were observed and the inner part of the tumor was discolored. These observations suggest that CEPA might suppress cancer cell growth through malnutrition due to a suppressive effect on tumor angiogenesis. In this study, the antiangiogenic effects of CEPA were investigated in vitro. CEPA at 5 micromol/L inhibited vascular endothelial growth factor (VEGF)-stimulated tube formation by human umbilical vein endothelial cells (HUVEC) (P < 0.05) and also inhibited VEGF-stimulated migration of HUVEC at a concentration of CEPA that suppressed tube formation (P < 0.05) but did not influence cell proliferation. The antiangiogenic mechanism of CEPA was investigated in vitro by measuring the secretion and expression of well-characterized angiogenic factors associated with cell migration, such as matrix metalloproteinases (MMP). CEPA at a concentration that suppressed tube formation inhibited secretion and mRNA expression of MMP2 and MMP9 in VEGF-stimulated HUVEC (P < 0.05). Our findings suggest that CEPA has potential use as a therapeutic dietary supplement for minimizing tumor angiogenesis.

The t10,c12 isomer of conjugated linoleic acid stimulates mammary tumorigenesis in transgenic mice over-expressing erbB2 in the mammary epithelium

Conjugated linoleic acid (CLA), a family of isomers of octadecadienoic acid, inhibits rat mammary carcinogenesis, angiogenesis, and lung metastasis from a transplantable mammary tumor. c9,t11-CLA, the predominant isomer in dairy products, and t10,c12-CLA, a component of CLA supplements, are equally effective. The objective of the current studies was to test the efficacy of these two CLA isomers in a clinically relevant breast cancer model. Transgenic mice over-expressing erbB2 in the mammary epithelium were fed control or 0.5% CLA-supplemented diets continuously from weaning. Unexpectedly, t10,c12-CLA stimulated lobular hyperplasia of the mammary epithelium and accelerated mammary tumor development, decreasing median tumor latency to 168 days of age compared with 256 and 270 days in the c9,t11-CLA and control groups, respectively. Metastasis was also increased by t10,c12-CLA, with percentage of tumor-bearing mice with lung metastasis 73, 14 and 31% in the t10,c12-CLA, c9,t11-CLA and control groups, respectively. A second study, in which CLA administration was initiated after puberty, confirmed the stimulatory effect of t10,c12-CLA on mammary tumor development and metastasis. Additionally, t10,c12-CLA, but not c9,t11-CLA, increased the size of the liver, heart, spleen and mammary lymph node. The effects of t10,c12-CLA were not specific to erbB2 transgenic mice, as t10,c12-CLA supplementation increased proliferation in the mammary epithelium of both wild-type FVB and FVB/erbB2 mice. Moreover, the number of terminal end buds, the mammary epithelial structures most sensitive to a carcinogenic insult, was increased 30-fold in FVB wild-type mice fed t10,c12-CLA. These data suggest that it would be prudent to avoid CLA supplements containing the t10,c12-CLA isomer. However, even though c9,t11-CLA was not efficacious in the erbB2 model, its ability to inhibit mammary tumor development in rat models suggests that it may have activity for prevention of some types of breast cancer.

Effects of trans-10,cis-12 conjugated linoleic acid on body fat and serum lipids in young and adult hamsters

The aim of the present work was to determine whether t-10, c-12 conjugated linoleic acid (CLA) feeding was able to reduce body fat accumulation and improve the serum lipid profile in adult hamsters fed an atherogenic diet, in order to compare these effects with those observed in young growing hamsters. Young and adult hamsters were fed semi-purified atherogenic diets supplemented with 0.5 % linoleic acid or 0.5% t-10, c-12 CLA for 6 weeks. Body weight and food intake were measured every two days. Adipose tissue from different anatomical locations, liver and gastrocnemious muscle were dissected and weighed. Cholesterol, triacylglycerols, non-esterified fatty acids and proteins were determined spectrophotometrically and water content by gravimetry. In young hamsters, no significant differences were found in food intake, final body weight and gastrocnemious muscle weight. White adipose tissue weights were reduced, liver weight was increased and cholesterol and triacyl-glycerols in both serum and liver were reduced. In adult hamsters, CLA feeding decreased food intake and adipose tissue weights. No changes were observed in other parameters. The present study demonstrates that age has an influence in hamster responsiveness to t-10, c-12 CLA because, although when this isomer is added to an atherogenic diet it reduces body fat accumulation in both young and adults hamsters, the lessening of the effects on serum lipids brought about by atherogenic feeding is only observed in young animals. Moreover, it is clear that liver is a target for CLA in young but not in adult hamsters.

The body fat-lowering effect of conjugated linoleic acid: a comparison between animal and human studies

Different reasons which justify differences between rodents and humans in body fat reduction produced by conjugated linoleic acid (CLA) could be proposed. The doses used in humans are lower than those used in rodents. Human experiments have been performed with CLA isomer mixtures instead of isolated isomers. The variable dilution of t-10, c-12, the active isomer, among different preparations might explain the reduced responsiveness in humans. Diet composition may modulate CLA effects on body fat accumulation. As far as human studies are concerned, a specific dietary pattern has not been established. As a result differences among studies and also among subjects in the same study are likely. In rodents, the effects of CLA vary with genotype, suggesting that genetic predisposition to fat accumulation can play an important role in the effectiveness of CLA. Human volunteers with different body mass index have participated in the published studies and even in the same experiment. So, differences in lipid metabolism among subjects could help to explain the discrepancies observed in the literature. Age and maturity may also be crucial. Experiments using rodents have been conducted with growing animals and there is little evidence of CLA effectiveness in adult animals. By contrast, human studies have been performed with adults. Inhibition of lipogenesis in white adipose tissue is one of the mechanisms which have been proposed to explain the body-fat lowering effect of CLA, but lipogenesis in this tissue is very low in humans. Another mechanism suggested is increased fatty acid oxidation in the liver associated with peroxisome proliferation, but humans are relatively insensitive to this effect.

[Linoleic conjugated acid: current interest in human nutrition]

Conjugated linoleic acid (CLA) is a group of positional and geometric isomers of linoleic acid. The major dietary sources of CLA are meat from rumiants and dairy products. There are also foods enriched in CLA (by modification animal feed or addition of commercial CLA from cartamo oil). However, the major isomer of CLA in natural food is cis-9,trans-11 and commercial CLA contains approximately equal amounts of cis-9,trans-11 and trans-10,cis-12 isomers. Although CLA is minor component of the diet, at present CLA has provoked intense scientific research accompanied by an advertising boom. This is due to the potential health effects demonstrated in animal and cell culture experiments including effects on body composition, specially a reduction in body fat mass and anticarcinogenic, antidiabetogenic and immune modulating effects. The results obtained in human volunteers are limited and even sometimes contradictory. This review focuses on recently studies in humans. To draw conclusions on CLA's potential interest as a functional ingredient, additional studies are needed to clearly define optimal level of CLA intake, short and long term effects and side effects of each individual CLA isomer in order to determine its safety and efficacy.

Association between dairy food consumption and weight change over 9 y in 19,352 perimenopausal women

BACKGROUND

Dairy foods may play a role in the regulation of body weight.

OBJECTIVE

We examined the association between changes in dairy product consumption and weight change over 9 y.

DESIGN

The study was conducted in 19 352 Swedish women aged 40-55 y at baseline. Data on dietary intake, body weight, height, age, education, and parity were collected in 1987-1990 and 1997. The intake frequencies of whole milk and sour milk (3% fat), medium-fat milk (1.5% fat), low-fat milk and sour milk (<or=0.5% fat), cheese, and butter were calculated at baseline and follow-up. The women were categorized into 4 groups according to their intake: 1) constant, <1 serving/d; 2) increased from <1 serving/d to >or=1 serving/d; 3) constant, >or=1 serving/d; and 4) decreased from >or=1 serving/d to <1 serving/d. Odds ratios (ORs) with 95% CIs for an average weight gain of >or=1 kg/y were calculated by using multivariable logistic regression analyses, with group 1 as the reference.

RESULTS

Mean (+/-SD) body mass index (in kg/m2) at baseline was 23.7 +/- 3.5. The constant (>or=1 serving/d) intakes of whole milk and sour milk and of cheese were inversely associated with weight gain; ORs for group 3 were 0.85 (95% CI: 0.73, 0.99) and 0.70 (95% CI: 0.59, 0.84) respectively. No significant associations were seen for the other 3 intake groups. When stratified by BMI, the findings remained significant for cheese and, for normal-weight women only, for whole milk and sour milk.

CONCLUSION

The association between the intake of dairy products and weight change differed according to type of dairy product and body mass status. The mechanism behind these findings warrants further investigation.

Conjugated linoleic acid intake in humans: a systematic review focusing on its effect on body composition, glucose, and lipid metabolism

Studies performed on different species show that the consumption of conjugated linoleic acid (CLA) leads to a loss of fat and total body weight, reduces the plasma concentrations of total and LDL cholesterol, and has an antiinflammatory effect. This article reviews the clinical trials on human beings that evaluate how mixtures of CLA isomers administered as supplements or CLA-enriched products can affect total body weight, body composition, plasma lipid profile, glycemia, insulinemia, insulin sensitivity, lipid oxidation, and inflammation. After analyzing the few studies published to date in reduced samples of healthy humans or patients with overweight, obesity, metabolic syndrome, or diabetes, we deduce that there is not enough evidence to show that conjugated linoleic acid has an effect on weight and body composition in humans. However, some of these studies have observed that the administration of various CLA isomers has adverse effects on lipid profile (it decreases HDL cholesterol concentration and increases Lp(a) circulating levels), glucose metabolism (glycemia, insulinemia or insulin sensitivity), lipid oxidation, inflammation, or endothelial function. Therefore, long-term randomized clinical trials, controlled with placebo, need to be made in large samples of patients to evaluate the efficacy and safety of CLA isomers before its indiscriminate use in human beings can be recommended.

Conjugated linoleic acid protects against age-associated bone loss in C57BL/6 female mice

Osteoporosis is one of the major causes of morbidity in the elderly. Inflammation exerts a significant influence on bone turnover, inducing the chronic form of osteoporosis. Dietary nutrition has the capacity to modulate inflammatory response. Therefore, nutritional strategies and lifestyle changes may prevent age-related osteoporosis, thereby improving the quality of life of the elderly population. Conjugated linoleic acid (CLA) has been shown to positively influence calcium and bone metabolism. Hence, this study was undertaken to examine the effect of CLA on bone mineral density (BMD) in middle-aged C57BL/6 female mice. After 10 weeks on diet, CLA-fed mice (14 months) maintained a higher BMD in different bone regions than corn oil (CO)-fed mice. The increased BMD was accompanied by a decreased activity of proinflammatory cytokines (such as tumor necrosis factor alpha, interleukin-6 and the receptor activator of NF-kappaB ligand) and decreased osteoclast function. Furthermore, a significant decrease in fat mass and an increase in muscle mass were also observed in CLA-fed mice compared to CO-fed mice. In conclusion, these findings suggest that CLA may prevent the loss of bone and muscle mass by modulating markers of inflammation and osteoclastogenic factors.

The role of conjugated linoleic acid in reducing body fat and preventing holiday weight gain

OBJECTIVE

The incidence of obesity and overweight in the US has increased considerably during the past two decades and currently affects 65% of the adult population. Research has indicated that small, yet irreversible, gains during the holiday season contribute to increases in weight during adulthood. Conjugated linoleic acid (CLA), a naturally occurring dietary fatty acid, has been found to reduce weight gain and dramatically decrease fat mass in animals. Although research in humans has shown inconsistent results, most studies have been of insufficient duration or have utilized body composition methods that are less accurate than the currently accepted criterion.

DESIGN

Randomized, double-blind, placebo-controlled study of 3.2 g/day CLA for 6 months.

SUBJECTS

Forty healthy, overweight subjects (age: 18-44 years; body mass index: 25-30 kg/m(2)).

MEASUREMENTS

Body composition by the four-compartment model, resting metabolic rate (RMR) by indirect calorimetry, self-reported physical activity and dietary intake, and blood chemistries were determined at baseline and after 6 months. Body weight was measured monthly during the pre-holiday season (August-October), holiday season (November-December) and post-holiday season (January-March). Adverse events were assessed monthly.

RESULTS

Compared to CLA, the placebo group showed a greater rate of weight gain during the holiday season (P=0.01). Within the placebo group, holiday weight change was significantly greater compared to the pre-holiday period (August-October) (P=0.03). Six-month change in body composition was improved with CLA compared to placebo (P=0.02), and body fat was significantly reduced within the CLA group (-1.0+/-2.2 kg, P=0.05). CLA had no effect on RMR, physical activity or dietary intake. The rate of reported negative emotions decreased significantly with CLA, although there was no difference in any other category of adverse event. In comparison to the placebo, CLA did not affect insulin resistance, blood lipids and markers of liver function or markers of inflammation, with the exception of a significant decrease in a biomarker of endothelial dysfunction.

CONCLUSION

CLA supplementation among overweight adults significantly reduced body fat over 6 months and prevented weight gain during the holiday season. Although no adverse effects were seen, additional studies should evaluate the effect of prolonged use of CLA.

Conjugated linolenic acid is slowly absorbed in rat intestine, but quickly converted to conjugated linoleic acid

We showed previously that alpha-eleostearic acid (alpha-ESA; 9Z11E13E-18:3) is converted to 9Z11E-conjugated linoleic acid (CLA) in rats through a Delta13-saturation reaction. To investigate this further, we examined the absorption and metabolism of alpha-ESA in rat intestine using a lipid absorption assay in lymph from the thoracic duct. In this study, we used 4 test oils [tung oil, perilla oil, CLA-triacylglycerol (TG), and pomegranate seed oil, containing alpha-ESA, alpha-linolenic acid (LnA; 9Z12Z15Z-18:3), CLA, and punicic acid (PA; 9Z11E13Z-18:3), respectively]. Emulsions containing the test oils were administered to rats, and lymph from the thoracic duct was collected over 24 h. The positional and geometrical isomerism of CLA produced by PA metabolism was determined using GC-electron impact (EI)-MS and (13)C-NMR, respectively; the product was confirmed to be 9Z11E-CLA. A part of alpha-ESA and PA was converted to 9Z11E-CLA 1 h after administration; therefore the lymphatic recoveries of alpha-ESA and PA were modified by the amount of recovered CLA. Cumulative recovery of CLA, alpha-ESA, and PA was lower than that of LnA only during h 1 (P < 0.05), and cumulative recovery of alpha-ESA and PA was significantly lower than that of LnA and CLA for 8 h (P < 0.05). Therefore, the absorption rate was LnA > CLA > alpha-ESA = PA. The conversion ratio of alpha-ESA to 9Z11E-CLA was higher than that of PA to 9Z11E-CLA over 24 h (P < 0.05). These results indicated that alpha-ESA and PA are slowly absorbed in rat intestine, and a portion of these fatty acids is quickly converted to 9Z11E-CLA.

Thematic review series: Patient-Oriented Research. Nutritional determinants of insulin resistance

Interpreting the literature relating to the nutritional determinants of insulin resistance is complicated by the wide range of methods used to determine insulin sensitivity. Excess adiposity is unquestionably the most important determinant of insulin resistance, although the effect may be tempered by a relatively high proportion of lean body mass. Weight loss is associated with improved insulin sensitivity. Thus, diet-related factors that promote excessive energy intake may be regarded as promoters of insulin resistance. In the context of energy balance, diets characterized by high intakes of saturated fat and low intakes of dietary fiber are associated with reduced insulin sensitivity. Total fat intakes greater than the usually consumed range appear to promote insulin resistance, although the relative proportions of total fat and carbohydrate within the usual range appear unimportant. Monounsaturated fatty acids with a cis configuration and fiber-rich carbohydrate foods appear to be appropriate substitutes for saturated fatty acids and rapidly digested glycemic carbohydrates. In animal studies, n-3 unsaturated fatty acids have been shown to enhance insulin sensitivity and fructose and sucrose to increase insulin resistance. However, human data are limited. Large prospective studies currently being conducted should confirm the most appropriate macronutrient composition of diets for preventing and treating insulin resistance as well as establishing whether a range of candidate genes explains the variation in response to dietary change.

Conjugated linoleic acid and human health: a critical evaluation of the evidence

PURPOSE OF REVIEW

This review critically evaluates studies investigating the effects of conjugated linoleic acid on human health, including effects on body composition, blood lipids, liver metabolism, insulin sensitivity and immune function. It focuses mainly on human intervention studies, but includes some reference to animal and cellular studies which provide insight into potential molecular mechanisms of action of conjugated linoleic acid.

RECENT FINDINGS

Human studies continue to report inconsistent effects of conjugated linoleic acid on human health. Some of these reports are based on overinterpretation of marginal effects of supplementation. Recent data suggest that the effects of the substance may be isomer dependent and that cis-9,trans-11 and trans-10,cis-12 conjugated linoleic acids have opposing effects on blood lipids and on metabolism in adipocytes and hepatic cells.

SUMMARY

Claims that conjugated linoleic acid is beneficial for health remain as yet unconvincing. Human studies investigating the effects of conjugated linoleic acid supplements have tended to use mixtures of isomers and have been inconsistent. More recent studies have attempted to use relatively pure preparations of single isomers and these studies suggest that the effects of conjugated linoleic acid may be isomer-specific. These recent data suggest a relative detrimental effect of trans-10,cis-12 conjugated linoleic acid on blood lipids. There appears to be little effect of conjugated linoleic acid on immune function and the effects on insulin sensitivity remain unclear.

Conjugated linoleic acid supplementation for 1 y does not prevent weight or body fat regain

BACKGROUND

Conjugated linoleic acid (CLA) is marketed as a safe, simple, and effective dietary supplement to promote the loss of body fat and weight. However, most previous studies have been of short duration and inconclusive, and some recent studies have questioned the safety of long-term supplementation with CLA.

OBJECTIVE

Our aim was to assess the effect of 1-y supplementation with CLA (3.4 g/d) on body weight and body fat regain in moderately obese people.

DESIGN

One hundred twenty-two obese healthy subjects with a body mass index (in kg/m2) > 28 underwent an 8-wk dietary run-in with energy restriction (3300-4200 kJ/d). One hundred one subjects who lost >8% of their initial body weight were subsequently randomly assigned to a 1-y double-blind CLA (3.4 g/d; n = 51) or placebo (olive oil; n = 50) supplementation regime in combination with a modest hypocaloric diet of -1250 kJ/d. The effects of treatment on body composition and safety were assessed with the use of dual-energy X-ray absorptiometry and with blood samples and the incidence of adverse events, respectively.

RESULTS

After 1 y, no significant difference in body weight or body fat regain was observed between the treatments. The CLA group (n = 40) regained a mean (+/-SD) 4.0 +/- 5.6 kg body weight and 2.1 +/- 5.0 kg fat mass compared with a regain of 4.0 +/- 5.0 kg body weight and 2.7 +/- 4.9 kg fat mass in the placebo group (n = 43). No significant differences in reported adverse effects or indexes of insulin resistance were observed, but a significant increase in the number of leukocytes was observed with CLA supplementation.

CONCLUSION

A 3.4-g daily CLA supplementation for 1 y does not prevent weight or fat mass regain in a healthy obese population.

Body fat-lowering effect of conjugated linoleic acid is not due to increased lipolysis

The ability of conjugated linoleic acid (CLA) to reduce adiposity may be due to changes in energy expenditure and/or direct effects on adipocyte lipid metabolism. The aim of the present work was to analyse if CLA supplementation modifies lipolytic activity in adipose tissue from hamsters fed on high-fat diet. Hamsters were divided into two groups and fed on diets supplemented with either 0.5% linoleic acid (control) or 0.5% trans-10,cis-12 CLA. After 6 weeks, animals were fasted overnight and adipose tissues were dissected and weighed. Adipocytes were isolated by collagenase digestion and incubated in Krebs-Ringer bicarbonate buffer with or without several agents acting at different levels of the lipolytic cascade. Adipocyte diameters were measured by microscopy. Adipose tissue DNA content was assessed by spectrophotometry. Animals fed on CLA diet showed significantly reduced adipose tissue mass. No differences between both groups was found for basal lipolysis, lipolytic effects of isoproterenol, forskolin, dibutyryl-cAMP and isobutylmethylxanthine, and pD2 for isoproterenol. A similar total DNA amount was found in adipose tissue of both groups, showing that CLA diet had no effect on total cell number per fat pad. Although DNA content per gram tissue, an indirect reverse index of cell size, was significantly increased in CLA fed hamsters, microscopy did not reveal differences in medium mature adipocyte diameter, nor in cell size distribution between both groups. These results suggest that adipose tissue size reduction induced by trans-10,cis-12 CLA intake is not due to changes in lipolysis. Reduced preadipocyte differentiation into mature adipocytes may account for this fat-lowering effect.

Increase of geometrical and positional fatty acid isomers in dark meat from broilers fed heated oils

Oxidation of polyunsaturated fatty acids leads to primary and secondary oxidation products. Compounds and amounts of these products vary, depending on the oxidative conditions. Because these oxidation products have different absorption and biological effects, we performed 2 different heating treatments on sunflower oil. The first was heating the oil at 190 to 195 degrees C for 28 h (i.e., very oxidized oil), and the other was heating at 60 degrees C for 12 d (i.e., peroxidized oil). In the frame of this study, we compared the fatty acid composition of a refined sunflower oil (fresh oil), peroxidized oil, very oxidized oil, and a mixture (1:1) of fresh and very oxidized oil (i.e., oxidized oil). Oil fatty acid compositions were affected by the heating treatments. In addition, different fatty acid isomers were formed during heating at 190 to 195 degrees C, and significant differences were found between their contents in the sunflower oils. We also studied the effect of feeding broilers with these oils and Zn and tocopherol supplements on the fatty acid composition of their raw dark meat. Various trans fatty acid isomers increased in dark meat from broilers fed oxidized and very oxidized oils. In addition, discriminant analysis showed that ditrans-conjugated linoleic acid content was able to distinguish dark chicken meat from chickens fed sunflower oils heated at 190 to 195 degrees C.

Conjugated linoleic acid promotes human adipocyte insulin resistance through NFkappaB-dependent cytokine production

We previously demonstrated that trans-10, cis-12 conjugated linoleic acid (CLA) reduced the triglyceride content of human adipocytes by activating mitogen-activated protein kinase kinase/extracellular signal-related kinase (MEK/ERK) signaling via interleukins (IL) 6 and 8. However, the upstream mechanism is unknown. Here we show that CLA increased (>or=6 h) the secretion of IL-6 and IL-8 in cultures containing both differentiated adipocytes and stromal vascular (SV) cells, non-differentiated SV cells, and adipose tissue explants. CLA isomer-specific induction of IL-6 and tumor necrosis factor-alpha was associated with the activation of nuclear factor kappaB (NFkappaB) as evidenced by 1) phosphorylation of IkappaBalpha, IkappaBalpha kinase, and NFkappaB p65, 2) IkappaBalpha degradation, and 3) nuclear translocation of NFkappaB. Pretreatment with selective NFkappaB inhibitors and the MEK/ERK inhibitor U0126 blocked CLA-mediated IL-6 gene expression. Trans-10, cis-12 CLA suppression of insulin-stimulated glucose uptake at 24 h was associated with decreased total and plasma membrane glucose transporter 4 proteins. Inhibition of NFkappaB activation or depletion of NFkappaB by RNA interference using small interfering NFkappaB p65 attenuated CLA suppression of glucose transporter 4 and peroxisome proliferator-activated receptor gamma proteins and glucose uptake. Collectively, these data demonstrate for the first time that trans-10, cis-12 CLA promotes NFkappaB activation and subsequent induction of IL-6, which are at least in part responsible for trans-10, cis-12 CLA-mediated suppression of peroxisome proliferator-activated receptor gamma target gene expression and insulin sensitivity in mature human adipocytes.