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Fish

Oily fish—including salmon, tuna, and mackerel—are rich in omega-3 fatty acids, compounds that help reduce harmful inflammation in the body. Chronic inflammation prevents your immune system from working properly, and can contribute to colds and flu as well as more serious diseases.

Omega 3s may fight colds on more than one front. In a placebo-controlled 2011 study published in Brain, Behavior and Immunity, medical students who took fish oil supplements for three months had lower inflammation levels and also fewer symptoms of anxiety—a condition that can itself weaken immune function.

Next: Oysters