Here are a few benefits to get you started, from Mike Barrett's article at Natural Society:
- Better Oral Health — This may seem odd since onions can cause bad breath, but chewing raw onion is known to improve the strength of the teeth and fight off bacteria which can cause tooth decay. Chewing some raw onion for 2 or 3 minutes could kill most germs in the mouth.
- Prevents Colon Cancer — A particular plant-derived flavonoid in onions, called quercetin, boosts the immune system while preventing the development of tumors. One study found that combining chemicals found in onions and turmeric reduced both the size and number of precancerous lesions in the human intestinal tract.
- Anti-Bacterial and Anti-Microbial Ingredients — Sulphides and thiosulfinates help to prevent illnesses such as E. coli, bacillus subtilis and salmonella.
The rest may be found here: http://naturalsociety.com/health-benefits-of-onions/