Advances in genetics and molecular biology indicate that susceptibility to chronic diseases such as coronary artery disease (CAD), hypertension, diabetes, obesity, osteoporosis, alcoholism, cancer, etc., to a great extent is genetically determined. Studies have shown that 50% of the variance in plasma cholesterol concentration is genetically determined, whereas 30%-60% of the variance in blood pressure is genetically determined. For fibrinogen, an independent risk factor for CAD, 15%-50% of the variance is genetically determined. In the U.K. population the variance for the fibrinogen level is 15% whereas in the Hawaiian population, the variance is 50%, indicating significant differences between populations. Among Australians, 75% of the variance in bone density is found to be genetically determined. Genetic variation influences the response to diet. For example, individuals with ApoE4 have higher cholesterol levels and a higher risk of CAD than those with ApoE3. Additional studies show that women of the ApoE 3/2 phenotype stand to benefit the least from a high polyunsaturate: saturate (P:S) diet because of reduction in the more 'protective' high density lipoprotein cholesterol (HDL-C), whereas men of the ApoE 4/3 phenotype showed the greatest improvement in the LDL/HDL ratio. Therefore a general recommendation to increase the polyunsaturated content of the diet in order to decrease the risk for CAD is not appropriate for women with ApoE 3/2 phenotype. Thus, specific information is needed to define the optimal diet for an individual.