Beta-glucans recovered from lion’s mane (Hericium erinaceus) processing by-products can act as potent prebiotics rather than waste material. When extracted using pulsed electric fields, the fibers (about 7–10% of dry weight) selectively fed beneficial microbes like Bifidobacterium and Lactobacillus, while driving a 30–50% rise in short-chain fatty acids, the key molecules that strengthen the gut barrier and dampen inflammation. The results indicate lion’s mane beta-glucans can actively reshape the gut ecosystem toward a more resilient, anti-inflammatory state, not just add generic fiber.