Informations: Red onions, in particular, contain anthocyanins special plant pigments in the flavonoid family that give red onions their deep color. ... Summary Red onions are rich in anthocyanins, which are powerful plant pigments that may protect against heart disease, certain cancers and diabetes. Packed With Nutrients. May Benefit Heart Health. Loaded With Antioxidants. Contain Cancer-Fighting Compounds. Help Control Blood Sugar. May Boost Bone Density. Have Antibacterial Properties. May Boost Digestive Health. Easy to Add to Your Diet.