The defense mechanism of our body is our immune system and a healthy immune system will ensure we do not contract diseases that are caused due to bacteria, fungus, and viral infections. Nature has many natural ways to help prevent free radicals from affecting our body. Onions are one of these natural ways to build a stronger immunity. The vitamin C present in onions is the reason onions are believed to protect us from many diseases. The phytonutrients present in onions help the antioxidant properties of the vegetable to take full effect.