Is Onion's Nutritious and Curing Elements Still Kept When Heated ?

Unfortunately cooking any vegetable results in loss of nutrients . Eating your produce uncooked keeps the enzymes and vitamins intact. Enzymes help to digest the food. When foods are cooked above 118F the enzymes do start to break down and you lose some of the natural benefit, but not all is lost - boiling is by far the worst method for any vegetable - steaming is best - loss of about 20%, for onions I would say stir fry in a little oil for 2 or 3 minutes - nutrient loss would be minimal. I like onions raw in a salad - that way you get all the benefits. I did once read though that certain nutrients in tomatoes are only actually released when cooked! I think the best way is to eat them both raw and cooked.