Influence of dietary fiber on lipid metabolism in meal-fed rats.

The effects of the four major components of dietary fiber--cellulose, hemicellulose, pectin and lignin--on lipid metabolism were studied in meal-fed Wistar rats maintained on a cholesterol-free semipurified diet for 21 days. Transit time was decreased and fecal weight increased compared to rats fed a fiber-free diet. Rats fed cellulose or lignin gained significantly less weight than rats fed hemicellulose or pectin. The fibers had no effect on serum cholesterol levels, but serum triacylglycerol levels were significantly higher in rats fed cellulose. Liver cholesterol levels were higher in cellulose-fed rats but liver triacylglycerol levels were highest in rats fed hemicellulose or pectin. Hepatic cholesterol 7 alpha-hydroxylase and HMG-CoA reductase activities were highest in rats fed cellulose and pectin, respectively. Epididymal fat cell size was similar in all groups but fat cell number was highest in pectin-fed rats. Perirenal fat cell size was greatest in rats fed cellulose or lignin and fat cell number in rats fed cellulose or hemicellulose. Lipoprotein lipase activity (per 10(6) cells) was elevated in epididymal fat of rats fed pectin and in perirenal fat of rats fed hemicellulose. Carcass lipid accumulation was highest in rats fed cellulose or lignin. Rats fed cellulose accumulated significantly higher levels of carcass cholesterol and triacylglycerol. Of the fibers fed, cellulose led to an accumulation of serum, liver and carcass lipid. The four fibers fed represent purified and altered forms of cellular components and the observed effects cannot be extrapolated to diets containing foods rich in one or another of these components.