Dietary medium chain fatty acids from coconut oil have little effects on postprandial plasma metabolite profiles in rainbow trout (Oncorhynchus mykiss)

• Postprandial plasma glucose, TG and NEFA were peaked at 9–12 h, 12h and 12–15 h.
• Fish fed diet FH had higher postprandial plasma HDL-C level and HDL-C/TC ratio.
• Plasma NEFA of fish fed diet CH was the highest.
• Dietary fat level affected the time-course changes in plasma profiles.
• Fat sources have little effects on the time-course changes in plasma profiles.

This study examined the effect of dietary medium-chain triglycerides supplied by coconut oil on postprandial plasma metabolite profiles in rainbow trout. The fish (initial body weight 71.3 ± 0.3 g, 17 °C) were fed one of four practical diets containing either 5% fish oil (FO low-fat, FL), 15% fish oil (FO high-fat, FH), 5% coconut oil (CO low-fat, CL) or 15% coconut oil (CO high-fat, CH) for 3 weeks. At the end of the trial, the fish were weighed and plasma sampled to determine glucose, non-esterified fatty acids (NEFA), triglyceride (TG), cholesterol, high density lipoprotein-cholesterol (HDL-cholesterol), and myeloperoxidase (MPO) at 3, 6, 9, 12, 15 and 24 h after the last meal. Plasma total ketone bodies (KB) were determined at 6, 12 and 24 h after meal. Blood nitroblue tetrazolium (NBT) tests were also performed in samples withdrawn at 24 h after meal.Plasma glucose was higher in fish fed the low fat level diet than those fed high fat level, and peaked at postprandial 9–12 h. Fish fed CH showed higher plasma TG than CL at 3 h after meal, and there was no significant difference in plasma TG at the other time points. The peak of TG appeared 12 h after the meal. No clear pattern was found for cholesterol and HDL-cholesterol (HDL-C) in any of the groups. However, fish fed diet FH had the highest postprandial plasma HDL-cholesterol level and HDL-C/cholesterol ratio. The peak of NEFA was observed at 12–15 h after meal and plasma NEFA of fish fed CH was the highest. Plasma total KB decreased with postprandial time, and fish of FH groups had higher KB than that of CL group at 6 h. Besides, NBT in fish fed FH was significantly higher than that of CH, but there were no differences in MPO between groups. In summary, time-course changes in plasma profiles related to dietary fat level were as expected whereas those related to dietary fat source were relatively small.