In female rats consuming 13% (w/v) HFCS-55 for 8 weeks, hepatic de novo lipogenesis is elevated compared to sucrose or fructose, as indicated by up-regulation of stearoyl-CoA desaturase-1 and increased oleic acid content, demonstrating activation of a specific metabolic pathway that enhances the conversion of saturated to monounsaturated fatty acids in the liver.

When HFCS-55 is consumed, the liver breaks down its high fructose content and uses it to build new fat molecules. This process turns on specific genes that make enzymes that convert saturated fats into monounsaturated fats like oleic acid. At the same time, the liver stops breaking down existing fats and fails to package new fats for export, causing fat to build up inside liver cells.