In high-cholesterol diets, enriched or not with onion, the SFA content in plasma and liver was diminished and associated to an increase in MUFA content, these results were in accordance with those found by Pita et al. (2002). Stearoyl-CoA can convert SFA into MUFA, which are favored substrates for acyl-CoA:cholesterol transferase (ACAT), enzyme that catalyzes the esterification of hepatic free cholesterol to an inert cholesteryl ester (Afonso et al., 2013). The SFA:MUFA ratio in plasma reflects the membrane phospholipid composition, and increases in this ratio have been implicated in diseases such as CVD, obesity, and diabetes (Ntambi & Miyazaki, 2004). Surprisingly, a low SFA:MUFA ratio was observed in plasma of rats fed the HC diet (1.04), more marked in rats fed the HCO diet (0.85) compared to rats fed the control diet (2.57). A similar pattern was detected in erythrocytes and liver.