EFFECTS OF A DIET RICH IN RESISTANT STARCH ON HEPATIC LIPID-METABOLISM IN THE RAT

The aim of this study was to examine the effects of the replacement of a large part of absorbed glucose by volatile fatty acids on hepatic l ipid metabolism. For this purpose, experiments were conducted in rats fed either a diet containing digestible wheat starch or amylase-resist ant cornstarch. Compared with the digestible wheat starch diet, plasma insulin was lower in rats fed the resistant cornstarch diet, and the fluctuations of insulinemia during the fed/postabsorptive period were smaller: The marked reduction of hepatic lipogenesis in rats fed the r esistant cornstarch diet (-52% compared with the digestible wheat star ch diet) resulted from the coordinated inhibition of all major enzymes implicated in the lipogenic pathway except acetyl CoA synthetase acti vity. This suggests that volatile fatty acids, particularly acetate, c onstituted the major source of acetyl CoA for lipogenesis, lather than glucose. However these modifications were not accompanied by a signif icant depressive effect on plasma triglycerides. In rats fed the resis tant cornstarch diet, changes in lipogenesis activity were accompanied by a reduction of glycolysis as shown by the net inhibition of glucok inase and pyruvate kinase. In parallel to these modifications, with th e resistant cornstarch phosphoenolpyruvate carboxykinase was markedly induced; with this diet, propionate should constitute the major glucon eogenic substrate removed by the liver. HMG CoA reductase was markedly induced in rats adapted to the resistant cornstarch diet (1.6-fold hi gher than with the digestible wheat starch diet); this could be relate d to the increased fecal bile acids excretion. A significant hypochole sterolemic effect of the resistant cornstarch diet was only observed d uring the postabsorptive period. In conclusion, hepatic fatty acid syn thesis is tightly controlled by carbohydrate availability, but the pos sibility that volatile fatty acids exert specific effects on lipogenes is could not be ruled out.