Antioxidants are compounds that help protect your cells from becoming damaged by substances called free radicals. Too many free radicals can cause oxidative stress in your body, which can lead to inflammation, as well as chronic conditions like cancer, heart disease, and diabetes. Shallots and garlics are rich in compounds with antioxidant activity, such as quercetin, kaempferol, and allicin. One study analyzing the antioxidant activity of 11 popular varieties of onion found that shallots and garlics contained the highest amounts. Another study compared the antioxidant strength of six Allium vegetables, noting that shallots and garlics had the second-highest strength after chives.