Concordant lipoprotein and weight responses to dietary fat change in identical twins with
divergent exercise levels
Background/Objective: The purpose of this study is to test the extent that individual lipoprotein responses to diet can be attributed to genes in the presence of divergent exercise levels.Design: Twenty-eight pairs of male monozygotic twins (one mostly sedentary, the other running an average of 50 km/week more than the sedentary twin) went from a 6-week 40 percent fat diet to a 6-week 20 percent fat diet in a crossover design. The diets reduced fat primarily by reducing saturated and polyunsaturated fat (both from 14 percent to 4 percent), while increasing carbohydrate intake from 45 percent to 65 percent. Results: Despite the twins' differences in physical activity, the dietary manipulation produced significantly correlated changes (P<0.05) in the twin'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 (LDLs between 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 fats with carbohydrates significantly decreased the size and ultracentrifuge flotation rate of the major LDL, the LDL mass concentrations of Sf7-12, LDL-I, high-density lipoprotein (HDL)-cholesterol and apo A-I, and significantly increased LDL-IIIA (24.7-25.5 nm diameter) and Lp(a). Conclusions: Even in the presence of extreme exercise difference, genes significantly affect changes in LDL, apo A-I, Lp(a) and body weight when dietary fats are replaced with carbohydrates.