Conjugated linoleic acids exhibit a strong fat-to-lean partitioning effect, reduce serum VLDL lipids and redistribute tissue lipids in food-restricted rats

The decrease in body fat in mice fed conjugated linoleic acid is due to increases in energy expenditure and energy loss in the excreta

We carried out energy balance studies in four groups of young, growing, 5-wk-old Balb-C mice (n = 12/group) that were either food restricted or nonrestricted and fed high fat diets (38 energy%) with or without 0.93 g/100 g conjugated linoleic acid (CLA) for 39 d. The energy in carcasses, excreta and food was measured in a bomb calorimeter. CLA lowered the percentage of the energy intake that was stored in the body from 1.9 +/- 0.8 to -2.3 +/- 0.7% (mean +/- SD, P < 0.05) in the nonrestricted mice and from 1.4 +/- 1.3 to -2.9 +/- 0.7% (P < 0.05) in the restricted mice. Thus, the CLA-treated mice had a net loss of body energy. The percentage of the energy intake eliminated in the excreta increased from 7.6 +/- 0.9% in controls to 8.7 +/- 1.0% (P < 0.05) in the CLA-treated mice that were nonrestricted and from 7.3 +/- 0.8 to 8.4 +/- 0.6 (P < 0.05) in the restricted mice. The amount of energy ingested minus the amount retained in carcasses and excreta equals the energy expenditure. The percentage of the energy intake that was expended as heat increased from 90.5 +/- 1.2 in controls to 93.6 +/- 1.5% (P < 0.05) in the CLA-treated nonrestricted mice and from 91.3 +/- 1.5 to 94.5 +/- 1.0% (P < 0.05) in the restricted mice. The lower energy storage in the CLA-fed mice was accounted for by an increase in the energy expenditure (74%) and by an increase in energy lost in the excreta (26%). Feeding CLA also increased liver weight, which may warrant further studies on the safety of CLA.

Influence of dietary conjugated linoleic acid isomers on early inflammatory responses in male broiler chickens

1. The influence of dietary conjugated linoleic acid isomer (CLA, 0 and 10 g/kg) on the metabolic and physiological responses to immune stimulation induced by a single injection of Salmonella enteritidis lipopolysaccharide (LPS) or repeated injections of LPS and Sephadex G-50 was determined in male broiler chicks. 2. In experiment 1, 10-d-old chicks were fed on experimental diets for 14 d and half of the birds fed on each diet were injected intraperitoneally with LPS (1.5 mg/kg body weight). In experiment 2,7-d-old chicks were fed on experimental diets for 18 d. Immune stimulation was started at 19 d old and continued for 5 d. Half of the birds fed on each diet were injected intraperitoneally with 0.25 mg/kg body weight of LPS at 19, 21 and 23 d of age, and with 250 mg/kg body weight of Sephadex at 20 and 22 d of age to stimulate the immune system. 3. In experiment 1, giving CLA prevented an increase in blood heterophil to lymphocyte ratio 7 h after a single injection of LPS, and increases in plasma ceruloplasmin and alpha 1 acid glycoprotein (AGP) 24 h after the injection, but not 7 h after the injection. CLA also prevented a decrease in food intake for 24 h after LPS injection. 4. In experiment 2, the CLA diet partially prevented reductions in body weight gain and weight gain to feed intake ratio caused by repeated injections of LPS and Sephadex. Feeding CLA prevented increases in plasma ceruloplasmin and AGP at 24 d of age caused by repeated injections of LPS and Sephadex, but not at 20 d of age. 5. These results suggest that feeding CLA alleviates some undesirable metabolic and physiological changes induced by immunological stimulation in male broiler chicks.

Effect of supplementation with conjugated linoleic acid on human serum lipids and body fat

Conjugated linoleic acid (CLA) is a natural component of meat and dairy products with anticarcinogenic, fat lowering, antiatherogenic and anticatabolic activity in animals. The purpose of this study was to examine the effect of CLA supplementation to humans on body fat, certain biochemical parameters of serum, and the CLA content of serum lipids. Twenty-two volunteers were divided into a study group and a control group in a doubly blind design. The study group received 0.7 g of CLA for four weeks and 1.4 g of CLA for the next four weeks, while the control group received placebo. Diet was controlled and no significant differences in energy or macronutrient intake were found between the two groups. Measurements were taken at baseline, four weeks, and eight weeks. The sum of the thickness of ten skinfolds, percentage body fat calculated from it and fat mass was significantly reduced in the CLA group during the second period (P < 0.004) but not overall during the study. Serum HDL-cholesterol decreased significantly (P < 0.001) and triacylglycerols as well as total cholesterol tended to decrease in the CLA group during the first period. The CLA content of serum non-esterified fatty acids, triacylglycerols, phospholipids, and cholesteryl esters increased gradually with supplementation; the CLA content of total serum lipids doubled at the end of the study compared to baseline. Phospholipids had the highest CLA content regardless of supplementation. These data indicate that supplementation with 0.7-1.4 g CLA daily for 4-8 weeks may modulate body fat and serum lipids, as well as increase the CLA content of serum lipids in humans.

Conjugated linoleic acid isomers have differential effects on triglyceride secretion in Hep G2 cells

The effect of different conjugated linoleic acid (CLA) isomers (trans-10,cis-12 (t10,c12)-CLA and cis-9,trans-11 (c9,t11)-CLA), compared with oleic acid (OA) and linoleic acid (LA), on hepatic lipid synthesis and secretion were investigated in Hep G2 cells. The cells were incubated in a medium containing 1 mmol/l fatty acid-bovine serum albumin (BSA) complex for 5 h, with BSA alone as control. [(3)H]Glycerol and [(14)C]acetate were used to monitor lipid synthesis and secretion. The results show that cellular uptake rates of these fatty acids were similar. Incubation with OA, t10,c12-CLA, c9,t11-CLA and LA resulted in 6-, 4-, 2- and 1.8-fold increases in intracellular [(3)H]triglyceride ([(3)H]TG) compared with incubation with BSA alone. OA, LA and c9,t11-CLA increased [(3)H]TG secretion 3.6-, 2.5- and 1.2-fold above the control, whereas t10,c12-CLA markedly suppressed the secretion of [(3)H]TG. Hepatic secretion of TG mass increased 3.5-, 3.3-, 2.7- and 1.5-fold in the cells incubated with OA, LA, c9,t11-CLA and t10,c12-CLA, respectively. Since the secreted TG is mainly contained in very low density lipoproteins (VLDL), the decreased ([(3)H])TG secretion by t10,c12-CLA reflects a diminished secretion of VLDL. With respect to cholesterol synthesis OA was more effective in stimulating the incorporation of [(14)C]acetate into cellular total cholesterol followed in descending order by LA, c9,t11-CLA and t10,c12-CLA. In conclusion, the biological properties of 18-carbon fatty acids are clearly influenced by both the number and (geometric) positions of their double bonds. Furthermore t10,c12-CLA is more effective than c9,t11-CLA on suppressing hepatic TG secretion in vitro.

Linoleic acid partially restores the triglyceride content of conjugated linoleic acid-treated cultures of 3T3-L1 preadipocytes

We have previously demonstrated that a crude mixture of commercially available conjugated linoleic acid (CLA) isomers suppressed triglyceride (TG) content and induced apoptosis in post-confluent cultures of murine 3T3-L1 preadipocytes. Furthermore, we found that 100 &mgr;M of trans-10, cis-12 isomer of CLA had a greater TG-lowering and apoptotic effect than the crude mixture of CLA isomers. Therefore, the purpose of this study was to: 1) compare the potencies of the two main isomers found in the crude mixture of CLA isomers, e.g. cis-9, trans-11 (41%) and trans-10, cis-12 (44%); and 2) determine if the TG-reducing actions of CLA could be attenuated by the addition of increasing levels of linoleic acid to the cultures. Preadipocyte differentiation was assessed on day 7 of the differentiation protocol by measuring TG content (per 10(6) cells), cell size, and lipid staining. In experiment 1, post-confluent cultures of 3T3-L1 preadipocytes treated for the first 6 d of differentiation with 100 &mgr;M of a crude mixture of CLA isomers or 44 &mgr;M of trans-10, cis-12 CLA had less TG content than all other cultures. In contrast, cultures supplemented with 41 &mgr;M of the cis-9, trans-11 CLA isomer had the same amount of TG as the BSA controls. In experiment 2, post-confluent cultures of 3T3-L1 preadipocytes treated for the first 6 d of differentiation with 50 &mgr;M trans-10, cis-12 CLA had less TG content and a greater number of smaller cells (10-12.5 microns) compared to all other treatments. CLA-treated cultures supplemented with increasing levels of linoleic acid (50-200 &mgr;M) had greater TG contents and greater numbers of larger cells (15-20 microns) than cultures treated with 50 &mgr;M of the trans-10, cis-12 CLA isomer alone. These data demonstrate that: 1) the TG-lowering effects of the crude mixture of CLA isomers is due almost exclusively to the trans-10, cis-12 isomer; and 2) linoleic acid partially reverses CLA's attenuation of TG content, suggesting that these unsaturated fatty acids may compete for incorporation into TG or phospholipid-derived eicosanoids that regulate preadipocyte differentiation.

The biologically active isomers of conjugated linoleic acid

Numerous physiological effects are attributed to conjugated linoleic acid (CLA). The purpose of this presentation is to consider these effects with respect to the cis-9,trans-11 and trans-10,cis-12 CLA isomers. We review previously published data and present new findings that relate to underlying biochemical mechanisms of action. Both isomers are natural products. The cis-9,trans-11 isomer is the principal dietary form of CLA, but the concentrations of this isomer and the trans-10,cis-12 isomer in dairy products or beef vary depending on the diet fed to cows or steers, respectively. The trans-10,cis-12 CLA isomer exerts specific effects on adipocytes, in particular reducing the uptake of lipid by inhibiting the activities of lipoprotein lipase and stearoyl-CoA desaturase. The trans-10,cis-12 CLA isomer also affects lipid metabolism in cultured Hep-G2 human liver cells, whereas both the cis-9,trans-11 and trans-10,cis-12 CLA isomers appear to be active in inhibiting carcinogenesis in animal models. We present new findings indicating that the cis-9,trans-11 CLA isomer enhances growth and probably feed efficiency in young rodents. Accordingly, the effects of CLA on body composition (induced by trans-10,cis-12 CLA) and growth/feed efficiency (induced by cis-9,trans-11 CLA) appear to be due to separate biochemical mechanisms. We also show that a 19-carbon CLA cognate (conjugated nonadecadienoic acid, CNA) inhibits lipoprotein lipase activity as effectively as CLA in cultured 3T3-L1 adipocytes. Presumably, CNA is metabolized differently than the 18-carbon CLA isomers, so this finding indicates direct activity of the administered compound as opposed to acting via a metabolite.

Conjugated linoleic acid: implications for human health

Conjugated linoleic acid (CLA) is being sold as a panacea that has the capability of reducing or eliminating cancer, preventing heart disease, improving immune function, and altering body composition to treat obesity or build lean body mass. Unfortunately, there has been very little published human research on CLA. This review will examine the literature on CLA and discuss the animal research on which the above claims are made. The limited human studies will be presented with an evaluation of the potential uses of CLA for human health and disease.