Hypolipidaemic effect of chemically different mucilages in rats: a comparative study

Different classes of fibres differ in their potential to lower lipid levels. In order to examine how chemically diverse fibres differ in their hypolipidaemic activity, mucilages of varying chemical composition isolated from three different sources were administered to experimental animals and the metabolism of lipids and lipoproteins was studied. The mucilages used were a galactomannan isolated from fenugreek (Trigonella foenum-graecum) seeds, a glucomannan from Dioscorea esculenta tubers and an arabinogalactan from Colocasia esculenta tubers. Rats were fed these mucilages at a dose of 4mg/100g body weight per d for 8 weeks and the changes in the levels of total cholesterol and triacylglycerols in serum, liver and aorta were analysed. All these mucilages decreased lipid levels both in serum and tissues. Among these mucilages, glucomannan showed the most hypolipidaemic effect followed by galactomannan and arabinogalactan. Further, hepatocytes were isolated from the livers of mucilage-fed rats and the synthesis and secretion of lipoproteins were studied using metabolic labelling. There was a decrease in the synthesis and secretion of apoB-containing lipoproteins, mainly VLDL, by hepatocytes isolated from mucilage-fed rats when compared to control (P < 0.05). This was further confirmed by pulse chase analysis. Among the different mucilages, mannose-rich glucomannan showed the most effect followed by galactomannan, and mannose-free arabinogalactan showed minimal effect. Comparison of relative viscosity and water-holding capacity showed that mannan-rich mucilages like galactomannan and glucomannan, which showed greater hypolipidaemic effect, had greater relative viscosity and water-holding capacity. The present results suggested that the hypolipidaemic effect of dietary fibre involves a decrease in hepatic production of VLDL and further that it varies with the nature of the fibre.