We examined the effects of feeding conjugated linoleic acids (CLA) to adult male hamsters on several components of energy metabolism and body composition. Hamsters (n = 54) were assigned for 6-8 wk to one of three diets: 1) a standard diet (in percentage energy: lipids, 33, carbohydrates, 49, and proteins, 18); 2) to the standard diet augmented with the 9c,11t-isomer of CLA to 1.6% of energy (R group); or 3) the standard diet augmented with the 9c,11t-isomer and the 10t,12c-CLA isomer to 3.2 (1.6 + 1.6) % of energy (CLA mix group). (15)N uniformly labeled milk-protein was included in the diet to measure the incorporation of dietary protein into liver and muscle. Basal metabolic rate, thermogenic response to feeding and energy expenditure during spontaneous activity or during an exercise at approximately 60% of VO(2max) were measured. Carnitine palmitoyltransferase-I (CPT-I), leptin, insulin and triiodothyronine concentrations, as well as the in vivo overall adiposity changes were also determined. After 6 wk, the whole-body triglyceride content determined in vivo by NMR was significantly higher in the R group than in the control and CLA mix groups. The CLA mix group differed from the others in the lack of body triglyceride accumulation between d 21 and d 45 of the study, and the appearance of a slight insulin-resistance (homeostatic model assessment index, P < 0.05). Paradoxically, the lack of effect on whole-body lipid oxidation was associated with a greater CPT-I-specific activity in tissues of both CLA-fed groups (P < 0.05). No other major effects of CLA feeding were detected. In conclusion, CLA supplementation in hamsters did not affect adipose weight or the components of energy expenditure despite a theoretically higher capacity of red muscle to oxidize lipids. Only a CLA mixture prevented whole-body triglyceride accumulation over time.

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The aim of our present study was to compare the efficiency of conjugated linoleic acids (CLA) and fish oil in modulating atherogenic risk markers. Adult male hamsters were given a cholesterol-rich diet (0·6 g/kg) for 8 weeks; the diet was supplemented with 5 g cis-9,trans-11-CLA isomer/kg, 12 g CLA mixture (CLA-mix)/kg, 12 g fish oil/kg or 12 g fish oil þ 12 g CLA-mix/kg. The plasma cholesterol status was improved only with the cis-9,trans-11-CLA (HDL-cholesterol and HDL-cholesterol:LDL-cholesterol ratio, P,0·05), but was of borderline significance for CLA-mix (HDL-cholesterol:LDL-cholesterol ratio, P¼ 0·06), with an increase (33 -40 %) in the liver lipoprotein receptors (scavenger receptor-type I and LDL ApoB/E receptor) and HDL-binding protein 2 (P,0·05). A 100 % pigment gallstones incidence and a slight insulin resistance (homeostatic model assessment index) were observed in the CLA-mix-fed hamsters (P¼ -0·031). In comparison, fish-oil feeding alone improved merely the scavenger receptor-type I and HDL-binding protein 2 liver status and faeces sterol output. For most of our present observations, the concomitant intake of fish oil and CLA-mix gave dominant effects that were exclusive and specific to one or the other oil. In conclusion, part of the beneficial effects of CLA in the present study can be ascribed to the cis-9,trans-11-isomer, and these did not generally overlap with those of fish oil. In addition, the CLA-mix effects are clearly affected by the marine (n-3) fatty acids. Conjugated linoleic acid: Rumenic acid: Fish oil: Lipid atherosclerosis risk markers: HamstersConjugated linoleic acid (CLA) is a collective term describing positional and geometrical isomers of linoleic acid. Among them, the cis-9,trans-11-isomer, so-called rumenic acid, occurs naturally in foodstuffs from ruminant animal fat sources. CLA have received growing attention in the past 10 years because of their pleiotropic biological activities. For instance, these fatty acids are effective anti-carcinogens, anti-atherosclerotic agents and potent modulators of the immune function (Pariza et al. 2001;Martin & Valeille, 2002). Studies dealing with the anti-atherosclerotic properties of CLA are scarce but promising. For instance, a CLA mixture (CLA-mix; 94·0 % (range 1-10 g/kg cis-9,trans-11 and trans-10,cis-12 isomers/kg of diet) decreased early aortic atherosclerosis when given to male hamsters receiving a pro-atherogenic diet (F 1 B strain; Wilson et al. 2000), and even caused regression of pre-established atherosclerosis in the male rabbit (New Zealand White; Kritchevsky et al. 2000) (10 g/kg diet). On the other hand, a detrimental effect on early aortic lesions outcome of a similar CLA-mix (5 g/kg diet) has been observed in C57Bl/6 mice fed a pro-atherogenic diet (Munday et al. 1999). Nevertheless, the studies dealing with the effect of CLA on the plasma lipid profile are less clear. Animal studies and studies with human subjects have had discordant results, as reviewed in Roche et al. (2001). In addition, animal experiments (hamste...