In summary, reducing dietary saturated fat is associated with an increase in LDL-receptor abundance of magnitude similar to the decrease in serum LDL-cholesterol. Thus, an important mechanism by which reductions in dietary saturated fatty acids decrease LDL-cholesterol in humans is through an increase in LDL-receptor number.

Polyunsaturated fats protect against cardiovascular disease by providing more membrane fluidity than monounsaturated fats, but they are more vulnerable to lipid peroxidation (rancidity). The large scale KANWU study found that increasing monounsaturated fat and decreasing saturated fat intake could improve insulin sensitivity, but only when the overall fat intake of the diet was low.[1] However, some monounsaturated fatty acids (in the same way as saturated fats) may promote insulin resistance, whereas polyunsaturated fatty acids may be protective against insulin resistance.[2][3] Studies have shown that substituting dietary monounsaturated fat for saturated fat is associated with increased daily physical activity and resting energy expenditure. More physical activity was associated with a higher-oleic acid diet than one of a palmitic acid diet. From the study, it is shown that more monounsaturated fats lead to less anger and irritability.[4]

In line with data in humans [8], feeding of dietary monounsaturated fat to nonhuman primates reduced LDL without lowering HDL, and in comparison to saturated and polyunsaturated fat, provided the lowest LDL to HDL ratio [9•]. On the other hand, replacement of some of the saturated fat with monounsaturated fat was associated with an even greater enrichment of LDL particles with cholesteryl oleate, a change in LDL particle composition that has been shown to confer atherogenicity [9•]. However, caution is needed in applying the results from animal experiments to humans.