The present invention is directed to methods of developing dietary guidelines, particularly associated with dietary consumption of fatty acids. We discovered an association of a polymorphic marker with regulation of plasma lipid levels in response to dietary intake of polyunsaturated fatty acids. Accordingly, the present invention provides methods for providing individualized guidance in design of dietary interventions to alter plasma lipid profiles by genotyping APOA5 locus, wherein the presence of APOA5-1131C, APOA5-3G, APOA5 IVS3+476A, and APOA5 1259C alleles or alleles that are found to be in tight linkage disequilibrium with APOA5-1131C, APOA5-3G, APOA5 IVS3+476A, and APOA5 1259C alleles, is indicative of the individual being susceptible to altered plasma lipid levels in response to intake of n-6 polyunsaturated fatty acids.