The present study investigated the effect of
dietary carbohydrates on metabolism, with special focus on
fatty acid bioconversion and flesh
lipid composition in two rainbow trout lines divergently selected for muscle
lipid content and fed with
vegetable oils. These lines were chosen based on previously demonstrated potential differences in LC-PUFA synthesis and
carbohydrate utilization. Applying a factorial study design, juvenile trout from the lean (L) and the fat (F) line were fed
vegetable oil based diets with or without gelatinised
starch (17.1%) for 12 weeks. Blood, liver, muscle, intestine and adipose tissue were sampled after the last meal. Feed intake and growth was higher in the L line than the F line, irrespective of the diet. Moderate
postprandial hyperglycemia, strong induction of hepatic
glucokinase and repressed
glucose-6-phosphatase transcripts confirmed the metabolic response of both lines to
carbohydrate intake. Further at the transcriptional level,
dietary carbohydrate in the presence of n-3 LC-PUFA deficient
vegetable oils enhanced intestinal
chylomicron assembly, disturbed hepatic lipid metabolism and importantly elicited a higher response of key desaturase and elongase
enzymes in the liver and intestine that endorsed our hypothesis. PPARĪ³ was identified as the factor mediating this dietary regulation of
fatty acid bioconversion
enzymes in the liver. However, these molecular changes were not sufficient to modify the
fatty acid composition of muscle or liver. Concerning the genotype effect, there was no evidence of substantial genotypic difference in lipid metabolism, LC-PUFA synthesis and flesh
fatty acid profile when fed with
vegetable oils. The minor reduction in plasma
glucose and
triglyceride levels in the F line was linked to potentially higher
glucose and
lipid uptake in the muscle. Overall, these data emphasize the importance of dietary macro-nutrient interface in evolving fish nutrition strategies.