Garlic
This potent onion relative contains the active ingredient allicin, which fights infection and bacteria. In one study, British researchers gave 146 people either a placebo or a garlic extract for 12 weeks; the garlic takers were two-thirds less likely to catch a cold. Another 2020 meta-analysis found that garlic consumption may lower the risk of colorectal cancer.
Shellfish
Selenium—plentiful in shellfish such as oysters, lobsters, crabs, and clams—helps white blood cells produce cytokines, proteins that help clear flu viruses out of the body.