The mechanisms by which inulin may elicit its lipid-lowering effect are not well elucidated. To examine the lipid-lowering potential of inulin and especially its effect on bile acid metabolism, male golden Syrian hamsters were fed semipurified diets containing 20 g/100 g fat, 0.12 g/100 g cholesterol and 0 (control), 8, 12 or 16% inulin for 5 wk. Plasma total cholesterol concentrations were significantly lowered by 18, 15 and 29% in hamsters fed 8, 12 and 16% inulin, respectively. Dietary inulin specifically decreased VLDL cholesterol, which was significantly lower in hamsters fed 16% inulin compared with controls (1.1 +/- 0.3 vs. 2.9 +/- 0.6 mmol/L). LDL and HDL cholesterol were not significantly affected by dietary inulin. Plasma triacylglycerol was significantly reduced by 40 and 63% in hamsters fed 12 and 16% inulin, respectively. Hepatic total cholesterol and particularly esterified cholesterol accumulation were significantly lower in hamsters fed 8% inulin compared with controls. All three levels of dietary inulin caused distinct alterations in the bile acid profile of gallbladder bile. Taurochenodeoxycholic acid was significantly lower, whereas glycocholic and glycodeoxycholic acid were greater in hamsters fed inulin. Daily fecal bile acid excretion (micromol/d) tended to be greater (P = 0.056) in inulin-fed hamsters compared with controls, whereas daily neutral sterol excretion was not affected. These data demonstrate that the lipid-lowering action of inulin is possibly due to several mechanisms, including altered hepatic triacylglycerol synthesis and VLDL secretion and impaired reabsorption of circulating bile acids.

Cereal Chem. 76(5): [788][789][790][791][792][793][794][795] This study examined the effects of various cereal fibers and various amounts of β-glucan on cholesterol and bile acid metabolism. Hamsters were fed semisynthetic diets containing 0.12% cholesterol, 20% fat, and either 16% total dietary fiber (TDF) from wheat bran (control) or 10% TDF from oat bran, 13% TDF from oat bran concentrate or barley grains, 16% TDF from oat fiber concentrate, barley flakes, or rye bran. After five weeks, plasma total cholesterol and liver cholesterol concentrations were significantly lower (20 and 50%, respectively) only in hamsters fed rye bran. Diets containing any of the oat ingredients or barley had no effect on total cholesterol. Changes in the pattern of biliary bile acids occurred in hamsters fed 16% TDF from barley flakes or 10% TDF from oat bran. Hamsters fed rye bran had a significantly higher fecal bile acid excretion when compared with controls fed wheat bran. Because rye bran caused the most pronounced lowering effect of total cholesterol despite the lowest content of β-glucan and soluble fibers, components other than β-glucan and soluble fibers seem to be involved in its hypocholesterolemic action. Since the effects of the oat and barley ingredients were not solely correlated to the β-glucan content, structural changes occurring during processing and concentrating of the products may have impaired the hypocholesterolemic potential of the β-glucans, and other factors such as solubility and viscosity of the fiber components seem to be involved.

Recent studies have suggested that monounsaturated fatty acid (MUFA)-rich dietary fats do not have the same plasma cholesterol-lowering effects whereby rapeseed oil was more effective than olive oil. This phenomenon could be explicable by the content of other fatty acids or plant sterols. To further evaluate the effects of different MUFA-rich oils (18:1-rich sunflower oil, rapeseed oil, olive oil) in comparison to polyunsaturated (PUFA)-rich oils (18:2-rich sunflower oil) and saturated fat (palm stearin) on cholesterol and bile acid metabolism, male Syrian golden hamsters were fed semipurified diets containing 5% fat and 0.2% cholesterol for 5 weeks. To test whether oil refining would have an impact on the cholesterol-lowering potential, unrefined and refined varieties of rapeseed and olive oil were included. After 5 weeks, plasma total cholesterol (TC) was highest with palm stearin (10.0 ± 2.6 mmol/l) while the MUFA- or PUFA-rich fats significantly lowered TC. The lowest TC concentrations were found with refined rapeseed, cold pressed rapeseed and 18:2-rich sunflower oil (6.7 ± 1.2; 7.1 ± 0.7 and 7.1 ± 0.7 mmol/l, respectively), whereas TC was 10–15% higher (not significant) with 18:1-rich sunflower, virgin and refined olive oil. Liver cholesterol concentrations were lowest in hamsters fed palm stearin or 18:2-rich sunflower oil while MUFA-rich fats increased hepatic cholesteryl ester accumulation, especially of cholesteryl oleate. There were no significant differences in the fecal neutral sterol and bile acid excretion. These data demonstrate that MUFA-rich dietary fats, e.g. rapeseed, olive and 18:1-rich sunflower oil, are comparable in their hypocholesterolemic potential and cause similar effects on plasma cholesterol as 18:2-rich sunflower oil in hamsters when the dietary cholesterol intake is moderate.

Different soluble dietary fibers known to alter cholesterol metabolism were fed to golden Syrian hamsters, and their specific impact on lipoproteins, biliary bile acid profile, and fecal sterol excretion was evaluated. Semipurified diets containing 20% fat; 0.12% cholesterol; and 8% of psyllium (PSY); high (hePE) and low (lePE) esterified pectin; or high (hvGG) and low (lvGG) viscous guar gum were fed for 5 wk. Compared to control, PSY caused a significant reduction in plasma cholesterol (2.9 +/- 0.5 vs. 5.5 +/- 0.5 mmol/L), whereas hePE, lePE, hvGG, or lvGG had no apparent effect on plasma lipids. Hepatic total and esterified cholesterol were substantially decreased with PSY, pectin and guar gum, whereby PSY produced the most pronounced effect. Distinctive changes existed in the bile acid profile related to the different fibers. In contrast to pectin and guar gum, PSY caused a significant increase in the cholate:chenodeoxycholate and the glycine:taurine conjugation ratio. Pectin and guar gum did not alter daily fecal neutral sterol excretion while PSY caused a 90% increase due to a higher fecal output. Daily fecal bile acid excretion and total fecal bile acid concentration were significantly increased by PSY, whereas hePE, lePE, hvGG, and lvGG revealed no or only minor effects. Taken together, the disparate hypocholesterolemic effects of PSY, pectin, and guar gum on cholesterol and bile acid metabolism in the hamster are possibly related to different physicochemical properties, e.g., viscosity and susceptibility to fermentation, affecting the fiber-mediated action in the intestine.

No abstract