Phytosterols such as β-sitosterol are plant-derived sterols structurally similar to cholesterol. They occur naturally in vegetable oils, nuts, seeds, and grains. β-Sitosterol competitively inhibits intestinal cholesterol absorption by displacing cholesterol from mixed micelles, leading to reduced serum LDL cholesterol levels. It exhibits anti-inflammatory and immunomodulatory properties and is used in functional foods and supplements. As a lipophilic compound, it integrates into cell membranes and may influence membrane fluidity. Extensive clinical studies support its safety and efficacy for cardiovascular health when consumed at 1.5–3 g/day. It is poorly absorbed (<5%) and primarily excreted via feces.