Normal human diet contains small amounts of phytosterols, mainly sitosterol and campesterol. Intestinal absorption of these plant sterols is low, about one tenth of that of cholesterol, such that their serum concentrations are also low, about 0.1 to 1% of the cholesterol levels. Like cholesterol they are transported by lipoproteins, mainly by LDL, and secreted unchanged in bile. Addition of plant sterols, or especially of their delta-5 saturated derivatives plant stanols into diet as fat-soluble esters inhibit cholesterol absorption and lower serum cholesterol similarly in short-term studies. Long-term consumption of plant stanol esters lowers serum cholesterol to the extent expected to reduce clinical manifestation of coronary heart disease by over 20% without detectable side effects, cholesterol lowering being especially effective in combination with cholesterol synthesis inhibitors statins.