Decrease of lipoprotein lipase activity in skeletal muscle in man during a short-term carbohydrate-rich dietary regime. With special reference to HDL-cholesterol, apolipoprotein and insulin concentrations

Seven men took part in a study in which the diet was changed from an ordinary mixed one to a fat-rich diet [>70% energy (E)] for 3 days followed by a carbohydrate-rich diet (>70% E) for 3 days. Blood was drawn and muscle biopsies [for analysis of lipoprotein-lipase (LPL) activity] were taken before the study and at the end of each diet period. Insulin, apolipoprotein (apo) B, A-I and A-II, cholesterol and triglyceride concentrations were determined in serum and the lipids also in the high density lipoproteins (HDL). Serum insulin was higher ( p < 0.01) during the carbohydrate-rich diet than during the fat-rich diet (12.0 ± 0.9 vs. 7.5 ± 0.5 mU/I, mean ± SEM), as were serum-triglycerides ( 2.42 ± 0.27 vs. 0,98 ± 0.07 mmole 1 , p < 0.001 ). Muscle LPL activity, on the other hand, was lower ( p < 0.01), 27.3 ± 6.1 vs. 75.1 ± 13.2 mU/g. HDL-cholesterol was 1.22 ± 0.08 during the carbohydrate-rich diet which was lower ( p < 0.01) than during the fat-rich diet, 1.45 ± 0.11. The concentration of apo A-I and A-II did not vary significantly. It is suggested that the increased insulin concentrations during a short-term, carbohydrate-rich diet may have a down-regulating effect on muscle LPL activity. Low muscle LPL activity may account for part of the elevation of serum triglycerides. An ineffective hydrolysis of VLDL-triglycerides may contribute to the variation in HDL-cholesterol concentration seen under these circumstances.