Effects of free fatty acids on the metabolic response to oral fructose in lean healthy humans.

OBJECTIVE

To study the effects of an experimental increase in plasma FFA concentration on fructose to glucose conversion, total hepatic glucose output and glycaemic response to oral fructose.

SUBJECTS

Six healthy subjects (three men, three women; age: 24.3 +/- 2.3 years; BMI: 21.6 +/- 0.8 kg/m2).

DESIGN

Each subject absorbed 0.5 g/kg of 13C-enriched fructose and randomly received either a triglyceride-heparin infusion or saline.

MEASUREMENTS

Total hepatic glucose output was traced with 6,6-2H2-glucose. Appearance in plasma of glucose synthesized from fructose was calculated from the isotopic enrichment in 13C of plasma glucose. Substrates oxidation was assessed with indirect calorimetry.

RESULTS

The triglycerides-heparin infusion increased FFA concentration before fructose as compared to saline (1086 +/- 40 vs 451 +/- 67 microM; p < 0.001) and lipid oxidation was 15% and 70% increased before and during fructose, respectively as compared to saline. Total hepatic glucose output, plasma appearance of glucose synthesized from fructose and glycaemic response were not affected. Glycogen storage over the first 3 h following fructose was increased (6.2 +/- 2.1 g vs 0.3 +/- 2.1 g; p < 0.01).

CONCLUSION

Triglycerides-heparin infusion did not stimulate plasma glucose appearance from fructose. Liver glucose-6-phosphate could have been produced in excess and diverted towards glycogen synthesis.