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Concordant lipoprotein and weight responses to dietary fat change in identical twins with divergent exercise levels ^{1 ,2 ,3}

¹ From the Lawrence Berkeley National Laboratory, Donner Laboratory, Berkeley, CA (PTW and RMK), and the Children's Hospital Oakland Research Institute, Oakland, CA (PJB, RR, and RMK)

Background: Individuals vary greatly in their lipoprotein responses to low-fat diets, with some of this variation being attributable to genes.

Objective: The purpose was to test the extent to which 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 twin mostly sedentary, the other running an average of 50 km/wk more than the sedentary twin) went from a 6-wk 40%-fat diet to a 6-wk 20%-fat diet in a crossover design. The diets reduced fat primarily by reducing saturated and polyunsaturated fat (both from 14% to 4%) while increasing carbohydrate intake from 45% to 65%.

Results: Despite the twins' differences in physical activity, the dietary manipulation produced significantly correlated changes (P < 0.05) in the twins' total cholesterol (r = 0.56); LDL cholesterol (r = 0.70); large, buoyant LDL [Svedberg flotation rate (S_f) 7–12; r = 0.52]; apolipoprotein A-I (r = 0.49); lipoprotein(a) (r = 0.49); electrophoresis measurements of LDL-I (LDLs between 26 and 28.5 nm in diameter; r = 0.48), LDL-IIB (25.2–24.6 nm; r = 0.54), and LDL-IV (22–24.1 nm; r = 0.50); and body weight (r = 0.41). Replacing fats with carbohydrates significantly decreased the size and ultracentrifuge flotation rate of the major LDL and the LDL mass concentrations of large, buoyant LDL; LDL-I; HDL cholesterol; and apolipoprotein A-I and significantly increased concentrations of LDL-IIIA (24.7–25.5 nm) and lipoprotein(a).

Conclusions: Even in the presence of extreme differences in exercise, genes significantly affect changes in LDL, apolipoprotein A-I, lipoprotein(a), and body weight when dietary fats are replaced with carbohydrates.

Key Words: Twins • low-fat diet • high-carbohydrate diet • lipoproteins • lipoprotein(a) • physical activity • LDL subclasses • apolipoproteins • cholesterol