Beta-glucans from oyster mushroom (Pleurotus ostreatus) can actively protect the gut and blood system during chemotherapy rather than just easing symptoms. Mice given oral beta-glucans at 500 mg/kg during 5-fluorouracil treatment reversed weight loss (from a 7% drop to a 1% gain), restored red blood cell counts by day 21, and preserved intestinal structure, with nearly full crypt survival (99.7 viable crypts vs 91.8 in chemo-only mice). The protection extended to bone marrow and colon tissue, indicating oyster mushroom beta-glucans may function as a true supportive therapy to chemotherapy-induced damage, not merely as a general immune tonic.