Beta-glucan is a fiber-type complex sugar (polysaccharide) derived from the cell wall of baker’s yeast, oat and barley fiber, and many medicinal mushrooms, such as maitake. In their natural states, yeast and mushrooms contain a mixture of beta-1,3-glucan and beta-1,6-glucan. Oats and barley contain a mixture of beta-1,3-glucan and beta-1,4-glucan. In addition to purified beta-1,3-glucan from these sources, you may see products listed as beta-1,3/1,6-glucan in the case of yeast-derived products and as beta-1,3/1,4-glucan when derived from oats. Similar (if not identical) properties have been shown for beta-glucan-rich extracts and purified beta-glucan derived from oats, baker’s yeast, and mushrooms.