GENETIC AND ENVIRONMENTAL-EFFECTS ON THE RESPONSE OF BLOOD CHOLESTEROL TO DIETARY CHANGE - A TWIN STUDY

While genetic factors appear to influence a single blood lipid measure ment, this twin sturdy was designed to explore the genetic influences on the change in blood lipid levels following diet change. Fifty monoz ygotic (MZ) and 44 like-sex dizygotic (DZ) pairs with total cholestero l (TC) levels of 7.5 mmol/l or less participated in this 6-week study. During the first 3 weeks they followed a diet with polyunsaturated to saturated fat (P:S) ratio of 0.3 and for the second 3 weeks they foll owed a diet with a P:S ratio of 0.8 with levels of total energy and to tal fat unchanged. Models based on the multivariate normal model for p edigrees were fitted to estimate the relative contributions of genes a nd environment to the change in TC and high-density lipoprotein choles terol (HDL-C) from the end of the low to the end of the high P:S ratio diet periods. After the high P:S ratio diet, TC fell by 9.3% and 8% w hile HDL-C fell 3.8% and 4.7% in MZ twins and DZ twins respectively. T hese changes were statistically significantly I elated to better dieta ry compliance, to baseline body mass index and to sex (women had a lar ger decrease in HDL-C than men). Genetic effects explained 17% and 29% of the variation in TC and HDL-C respectively, neither of these being statistically significantly different from no genetic effect. The sma ll genetic contribution to changes in blood lipid levels following an increase in the P:S ratio of the diet suggests that dietary interventi on can be successful regardless of genotype in people with a blood cho lesterol of 7.5 mmol/l or less.