Is muscle lipoprotein lipase inactivated by ordinary amounts of dietary carbohydrates?

Lipoprotein metabolism was investigated in 12 patients, healthy except for renal stone disease, who received a high-protein experimental diet for 2 weeks under metabolic ward conditions. The results were compared with those after 2 weeks on a control diet of ordinary composition. The patients were randomly allocated to begin with the control or experimental diet. The energy contributions from protein, carbohydrate and fat were 12, 48 and 41 per cent in the control diet and 29, 31 and 41 per cent in the experimental diet, respectively. Fasting concentrations of very-low-density lipoprotein (VLDL) triglycerides and cholesterol were lower with the high-protein than with the control diet (0.69 vs 1.4 mmol/l, P less than 0.0001, and 0.33 vs 0.47 mmol/l P less than 0.01, respectively). High-density lipoprotein cholesterol tended to be higher (0.05 less than P less than 0.10) with the high-protein diet. Lipoprotein-lipase (LPL) activity in skeletal muscle and the fractional catabolic rate constant of an intravenous fat tolerance test were higher with the high-protein than with the control diet (38 vs 21 mU/l, P less than 0.01, and 5.1 vs 3.6 mU/l, P less than 0.001, respectively). Neither fasting blood glucose, intravenous glucose tolerance nor insulin concentrations differed between the two dietary periods. These findings indicate that an 'ordinary' intake of refined carbohydrates has an inhibitory effect on the muscle LPL activity, thereby increasing the VLDL level and slightly decreasing the level of high-density lipoproteins, which may be of relevance for the atherosclerotic process.