“When fresh garlic is chopped or cut, you activate an enzyme called alliinase,” says gastroenterologist and Fiber Fueled author Will Bulsiewicz, MD. The alliinase, he explains, converts alliin (a sulfoxide in fresh garlic) to a compound called allicin, which is antibacterial, antiviral, and antifungal. (It’s also scientifically linked to being good for the heart.)