The LDL cholesterol (LDLC) response to fatty acid change is in part mediated by the APOE genotype, with E4 individuals (25% of the UK population) being most responsive to changes in dietary fats, showing greater reductions when low levels of saturated fats or fish oils are consumed and greater increases when high levels of these fats are consumed. Therefore the aims of the present study is to understand the mechanism that regulates the higher LDLC response associated with saturated fatty acids and fish oil consumption in healthy men prospectively recruited based on their APOE genotype.