We studied the role of casein and its hydrolysates in the inhibition of lipase and its binding ability with bile acids, by changing the activity of pancreatic lipase and digesting fats. It was concluded that preliminary hydrolysis of pepsin proteins in the stomach not only further improves their hydrolysis under the influence of proteolytic enzymes of pancreatic juice (tryptic attack of proteins), but also reduces their binding capacity with bile acids and improves hydrolysis of fats under the influence of pancreatic lipase. This fact is probably more important for the hydrolytic function of the stomach than the tryptic attack of proteins in the stomach and the main evolutionary factor in the preliminary digestion of proteins with gastric juice.