Background/Objective: The purpose of this study is to testthe extent that individual lipoprotein responses to diet can beattributed to genes in the presence of divergent exercise levels.Design:Twenty-eight pairs of male monozygotic twins (one mostly sedentary, theother running an average of 50 km/week more than the sedentary twin) wentfrom a 6-week 40 percent fat diet to a 6-week 20 percent fat diet in acrossover design. The diets reduced fat primarily by reducing saturatedand polyunsaturated fat (both from 14 percent to 4 percent), whileincreasing carbohydrate intake from 45 percent to 65 percent. Results:Despite the twins' differences in physical activity, the dietarymanipulation produced significantly correlated changes (P<0.05) in thetwin's total cholesterol (r=0.56), low-density lipoprotein(LDL)-cholesterol (r=0.70), large, buoyant LDL (Sf7-12, r=0.52), apo A-I(r=0.49), Lp(a) (r=0.49), electrophoresis measurements of LDL-I (LDLsbetween 26 and 28.5 nm diameter, r=0.48), LDL-IIB (25.2-24.6 nm, r=0.54),LDL-IV (22-24.1 nm, r=0.50), and body weights (r=0.41). Replacing fatswith carbohydrates significantly decreased the size and ultracentrifugeflotation rate of the major LDL, the LDL mass concentrations of Sf7-12,LDL-I, high-density lipoprotein (HDL)-cholesterol and apo A-I, andsignificantly increased LDL-IIIA (24.7-25.5 nm diameter) and Lp(a).Conclusions: Even in the presence of extreme exercise difference, genessignificantly affect changes in LDL, apo A-I, Lp(a) and body weight whendietary fats are replaced with carbohydrates.
