Facts about onions. Chefs started using them 5,000 years ago to spice up their cooking. Eaten ram onions are good for unblocking stuffed nose. Onions are low in calories and a good source of vitamin C, calcium, potassium and fiber. They get their distinctive smell by soaking up sulphur from the soil. Cooking destroys the eye watering agent. They help reduce cholesterol if eaten after a fatty meal. They help circulation.