Effect of low dietary levels of glucose, fructose and sucrose on rat lipid metabolism

Abstract

The effects of dietary carbohydrates on lipid metabolism have been investigated in rats maintained on diets containing 12 % glucose, fructose or sucrose and appreciable quantities of starch. The changes in hepatic rates of synthesis and catabolism of cholesterol and fatty acids as well as of triglycerides and phospholipids were studied to determine the relative influence of the three sugars on serum lipid concentrations. Marked increase in serum cholesterol results from feeding a sucrose diet, while elevation of serum neutral lipids is obtained with regimens containing fructose and sucrose. The effects are mainly due to the stimulation of rates of lipogenesis, associated with increments in the activities of enzymes of the hexose monophosphate oxidative pathway in the liver, coupled with relative lowering of the catabolic rate of specific lipid classes on respective carbohydrate regimens. Increased rates of triglyceride synthesis in the liver are responsible for elevated serum neutral lipid concentrations in rats on fructose and surcrose diets and are related to the high-α-glycerophosphate dehydrogenase activity in the liver of these animals. Evidence of induced phospho-fructokinase activity by fructose feeding has also been obtained and may be of significance in maintaining a high rate of supply of α-glycerophosphate via dihydroxy-acetone phosphate. Although glucose was found to stimulate hepatic cholesterolo-genesis, it reduced the serum cholesterol level by simultaneously maintaining a high rate of sterol catabolism in the liver. In spite of low sterol degradation rates in the liver of rats fed a fructose regimen, the serum cholesterol level was not significantly altered because hepatic cholesterol synthesis was depressed due to a relative increase in the rate of hepatic fatty acid synthesis from acetate.