β-Sitosterol—Dietary sources and role in cancer and diabetes management

β-Sitosterol is a major bioactive constituent and the most abundant phytosterol in nuts, seeds, and vegetable oils. It is structurally similar to cholesterol, except for the addition of the ethyl group. The primary benefit of β-sitosterol is that it lowers the body's absorption of low-density lipoprotein, or “bad” cholesterol. Research efforts to date and information from the available literature have demonstrated that β-sitosterol has many pharmacological benefits to improve human health; it effectively prevents heart diseases, cancer, and diabetes. To date, many investigations on β-sitosterol have been conducted in in vitro and in vivo studies. There are considerable research gaps because there are almost no clinical studies to examine the safety and effectiveness of β-sitosterol for various human diseases. This review aims to discuss the dietary sources and variations of β-sitosterol in food crops and how it can successfully prevent cancer and diabetes, including the mechanism underlying these benefits. In addition, we also discuss the research gaps and provide our perspective on future research to propose β-sitosterol as a nutraceutical candidate to prevent human diseases.