ß-Glucans (or beta-glucans) are polysaccharides occurring in the bran of cereal grains, the cell wall of baker's yeast, certain types of fungi, and many kinds of mushrooms. The cereal based beta-glucans occur most abundantly in barley and oats and to a much lesser degree in rye and wheat.

Beta glucan has been found to help to reduce cholesterol. On January 21, 1997, the U.S. Food and Drug Administration (FDA) approved a health claim on food products containing beta glucan. The claim states that "a diet high in soluble fiber from whole oats (oat bran, oatmeal and oat flour) and low in saturated fat and cholesterol may reduce the risk of heart disease".

Beta glucan also helps to improve the body’s immune system defense against foreign invaders by enhancing the ability of macrophages, neutrophils and natural killer cells.  

References

Food and Drug Administration, Human and Human Services (1996) Food labeling: health claims; oats and coronary heart disease: proposed rule. Fed. Regist. 61:296-313. ,FDA Talk Paper (1997) FDA allows whole oat foods to make health claim on reducing the risk of heart disease 1997Available at: http://www.cfsan.fda.gov/ lrd/tpoats.html. Accessed April 27, 2001., DHHS/FDA. 1997. Food labeling: Health claims; oats and coronary heart disease. Dept. Health and Human Services/Food and Drug Administration. Fed. Reg. 62: 3584-3601; Tsukada, C; Yokoyama H, Miyaji C, Ishimoto Y, Kawamura H, Abo T (January 2003). "Immunopotentiation of intraepithelial lymphocytes in the intestine by oral administrations of beta-glucan". Cellular immunology 221 (1): 1–5. United States: Academic Press. doi:10.1016/S0008-8749(03)00061-3. ISSN 0008-8749. PMID 12742376.