| Summary: | To ensure responsible use of the valuable marine ingredients a major effort is being invested in understanding effects of replacing fish meal and fish oil partially or completely with plant proteins and vegetable oils in aquaculture diets. Decreased dietary n-3/n-6 ratio and cholesterol levels and the introduction of vegetable oil derived phytosterols may affect Atlantic salmon health as well as nutritional product quality. Atlantic salmon plasma cholesterol is naturally very high being more than twice the upper range for healthy humans (11 mM in salmon vs 5 mM for healthy humans). Increased plasma and LDL cholesterol is a known risk factor for the development of cardiovascular disease in humans and phytosterols are known to lower plasma cholesterol. In Atlantic salmon, however, the role of dietary phytosterols as cholesterol lowering agents is still unexplored. The aim of the study was to investigate if the cholesterol metabolism and plasma cholesterol levels were altered in seawater phase Atlantic salmon when fed diets with either fish oil (FO) or vegetable oil (VO) based feeds for 6 months. The fish were fed diets with a high and constant inclusion of plant proteins, and either fish oil (FO) or 80 % of the FO replaced by olive oil (OO), rapeseed oil (RO) or soybean oil (SO). These oils were selected for their different levels of phytosterols and n-3/n-6 ratios to make it possible to determine whether it was the sterol composition of the feeds or the fatty acid composition being the main factor affecting fish cholesterol metabolism. Neither plasma nor lipoprotein cholesterol differed at any sampling point between Atlantic salmon fed the different experimental diets, indicating that cholesterol levels is metabolically regulated also in Atlantic salmon. Phytosterols tended to accumulate in liver, especially in the fish fed RO, which was the diet with the highest content of phytosterols. An increased mRNA expression of genes encoding for proteins involved in cholesterol synthesis (ACAT2, DHCR7 and SREBP2) was ...
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