[Fructose vs. glucose in total parenteral nutrition in critically ill patients]

Parenteral nutrition required following surgery or injury should not only meet post-aggression caloric requirements but also match the specific metabolic needs so as not to worsen the metabolic disruptions already present in this situation. The primary objective of parenteral nutrition is body protein maintenance or restoration by reduction of protein catabolism or promotion of protein synthesis or both. Whether all parenteral energy donors, ie., glucose, fructose, other polyols, and lipid emulsions, are equally capable of achieving this objective continues to be a controversial issue. The objective of the present study was to answer the following questions: (1) Do glucose and fructose differ in their effects on the metabolic changes seen following surgery or injury, the changes in glucose metabolism in particular? (2) Can the observation of poorer glucose utilization in the presence of lipids be confirmed in ICU patients?

A prospective, randomized clinical trial has been conducted in 20 aseptic surgical ICU patients to generate an objective database along these lines by performing a detailed analysis of the metabolic responses to different parenteral nutrition protocols. The effects of a glucose solution+lipid emulsion regimen vs fructose solution+lipid emulsion regimen on a number of carbohydrate and lipid metabolism variables were evaluated for an isocaloric (carbohydrates: 0.25 g/kg body weight/h; lipids: 0.166g/kg body weight/h) and isonitrogenous (amino acids: 0.0625 g/kg body weight/h) total nutrient supply over a 10-h study period.

A significantly smaller rise in blood glucose concentrations (increase from baseline: glucose+lipids P<0.001 vs fructose+lipids n.s.) suggested that fructose had a small effect, if any at all, on glucose metabolism. Serum insulin activity showed significant differences as a function of carbohydrate regimen, i.e. infusion of fructose instead of glucose produced a less pronounced increase in insulin activity (increase from baseline: glucose+lipids P<0.001 vs fructose+lipids P<0.01). Impairment of glucose utilization by concomitant administration of lipids was observed neither in patients who first received glucose nor in those who first received fructose.

As demonstrated, parenteral fructose, unlike parenteral glucose, has a significantly less adverse impact than glucose on the glucose balance, which is disrupted initially in the post-aggression state. In addition, the less pronounced increase in insulin activity during fructose infusion than during glucose infusion can be assumed to facilitate mobilization of endogenous lipid stores and lipid oxidation. Earlier workers pointed out that any rise in free fatty acid and ketone body concentrations in the serum produces inhibition of muscular glucose uptake and oxidation, and of glycolysis. These findings were recorded in a rat model and could not be confirmed in our post-aggression state patients receiving lipid doses commensurate with the usual clinical infusion rates. The serious complications that can result from hereditary fructose intolerance are completely avoidable if a careful patient history is taken before the first parenteral use of fructose. If the patient or family members and close friends, are simply asked whether he/she can tolerate fruit and sweet dishes, hereditary fructose intolerance can be ruled out beyond all reasonable doubt. Only in the extremely rare situations in which it is not possible to question either the patient or any significant other, a test dose will have to be administered to exclude fructose intolerance. The benefits of fructose-specific metabolic effects reported in the literature and corroborated by the results of out own study suggest that fructose is an important nutrient that contributes to metabolic stabilization, especially in the post-aggression phase and in septic patients. Hyperglycaemic states are largely prevented and fewer patients require ex