Current Issues in Fructose Metabolism

Abstract

The ingestion of fructose, particularly in refined form, has significantly increased in the North American diet over the last two decades. The unique way in which fructose is metabolized has given rise to much research examining whether fructose is advantageous in appetite control, exercise endurance, and disease states such as diabetes. Overall, there is very little evidence that modest amounts of fructose have detrimental effects on carbohydrate and lipid metabolism in nondiabetic or NIDDM subjects or that its use is particularly advantageous compared to that of other sugars. However, fructose can cause insulin and triglyceride levels to rise dramatically, and hence be potentially harmful, in a subgroup of NIDDM subjects who have concomitant pronounced hypertriglyceridemia. Large doses of fructose should also be avoided by subjects with gout because of the hyperuricemia which may result. No evidence exists that fructose has any clear advantages over glucose in regard to exercise endurance. Similarly there is no conclusive evidence that physiologic amounts of dietary fructose exacerbate copper deficiency or aid in weight control.

Differential effects of hyperinsulinemia and carbohydrate metabolism on sympathetic nerve activity and muscle blood flow in humans.

“…In this regard, our data provide direct evidence that fructose infusion in the amounts used in the present experiments is accompanied by a 22% increase in glucose oxidation. Thus, even though some of the precise steps involved in fructose metabolism are still unknown, there is agreement that a substantial part of this metabolism is taking place in skeletal muscle (33). In the present studies, such stimulation ofmuscle carbohydrate metabolism during fructose infusion was not associated with sympathetic activation and vasodilation in skeletal muscle.…”

Dietary Fruits and Vegetables and Cardiovascular Diseases Risk

“…Because of its low glycemic index, fructose was suggested as an alternative sweetener for diabetic patients (Henry et al, 1991). However, in patients with overt hyperglycemia and insulin deficiency, fructose may be associated with a greater increase in blood glucose concentrations than in diabetic patients with less elevated blood glucose concentrations (Swanson et al, 1992).…”

Inclusion of Low Amounts of Fructose With an Intraduodenal Glucose Load Markedly Reduces Postprandial Hyperglycemia and Hyperinsulinemia in the Conscious Dog

“…For this reason, the use of fructose as a substitute for dietary sucrose or dextrose has been examined as a potential therapeutic intervention for individuals with diabetes. However, in studies in which the effects of fructose on glucose metabolism were examined after several days or weeks of carbohydrate feeding (47,71,72), it has been shown that the conversion of glucose to glycogen, glucose oxidation, and lipid synthesis in the liver, muscle, and adipose tissues decreased. These adverse effects mean that substitution of fructose for glucose in the diet carries a significant risk (71).…”

“…However, in studies in which the effects of fructose on glucose metabolism were examined after several days or weeks of carbohydrate feeding (47,71,72), it has been shown that the conversion of glucose to glycogen, glucose oxidation, and lipid synthesis in the liver, muscle, and adipose tissues decreased. These adverse effects mean that substitution of fructose for glucose in the diet carries a significant risk (71). The difference in the amount of fructose used in the above studies versus the present experiments must be stressed.…”