Plant sterols, also known as phytosterols, are natural compounds found in plants that are similar to cholesterol but are made in plants. They are found in the highest amounts in vegetable oils, nuts, seeds, and grain products such as bread and cereals. Plant sterols can help reduce cholesterol levels by limiting the amount of cholesterol that is able to enter the body, and some plant sterols might also reduce how much cholesterol is made in the body. The cell structure of plant sterols looks and acts like cholesterol, so it competes with cholesterol for absorption by the digestive system. When the body digests plant sterols instead of cholesterol, it removes some of the cholesterol as waste, resulting in lower cholesterol levels and improved health.

Plant sterols are essential for all eukaryotes, and plant cells synthesize an array of sterol mixtures in which sitosterol and stigmasterol predominate. Sitosterol regulates membrane fluidity and permeability in a similar manner to cholesterol in mammalian cell membranes, and plant sterols can also modulate the activity of membrane-bound enzymes. Plant sterols are not recommended for people with sitosterolemia, a genetic disorder in which cholesterol and plant sterols build up in the body, and high plant sterol levels may cause an increased risk of early atherosclerosis.

Plant sterols can be present in the free form and as fatty acid esters and glycolipids, and the bound form is usually hydrolyzed in the small intestines by pancreatic enzymes. Some of the sterols are removed during the deodorization step of refining oils and fats, without, however, changing their relative composition. Plant sterols are also available in dietary supplements, and people commonly use plant sterols for lowering cholesterol levels, heart disease, colon cancer, stomach cancer, obesity, and heart attack. However, there is no good scientific evidence to support many of these other uses.