It is well known that dietary proteins affect lipid metabolism. However, the number of proteins examined in this connection is limited. Therefore, three feeding experiments were carried out to investigate the effects of dietary plant proteins like soy, pea and lupine proteins and animal proteins isolated from pork, beef, turkey and fish fillets, on lipid metabolism and the mechanisms behind it. To mimic western diets we used lard as dietary fat and added cholesterol (0.5 g/kg diet). In each experiment, growing male Sprague Dawley rats were fed the experimental diets for about three weeks in a restricted feeding regime. In the first two experiments, the diets varied only in the protein source, while in the third experiment, all plant protein diets were supplemented with DL-methionine, and the lupine diet additionally with lysine. As parameters of lipid metabolism, the concentrations of cholesterol and triglycerides in the plasma, lipoproteins and liver and the faecal excretion of bile acids were determined. To analyse the mechanism at the genetic level semi-quantitative RT-PCR were performed for selected genes involved in the lipid metabolism as well as cDNA macro arrays. All plant proteins lowered the cholesterol concentrations in liver and very low density lipoproteins and the triglyceride concentrations in plasma, lipoproteins and liver compared with casein. Beef and turkey protein exerted similar effects like casein, but pork protein lowered triglyceride concentration in plasma and liver significantly. The fish protein lowered the cholesterol concentration in high density lipoproteins, but increased free and esterified cholesterol concentration in liver; the triglyceride concentration in plasma and lipoproteins again was lowered. The gene expression studies showed that dietary proteins affect lipid metabolism by influencing the expression of genes involved in lipid homeostasis. The different amino acid composition of the dietary proteins might be in part responsible for their different effects.