Onions and garlic help prevent cancer

Powerful antioxidants in onions and garlic may offer protection MSNBC 2/2/07 "In laboratory studies, certain natural compounds in onions and garlic have demonstrated cancer protection. Now population studies published in recent months provide further evidence of the link between onions and garlic and a lower risk of cancer...People who used the most onion or garlic about a half-cup of chopped onion daily and a self-assessed “high” garlic consumption were from 10 percent to 88 percent less likely to have various types of cancer than those who said they used little or none...Laboratory studies have shown that onion and garlic compounds can increase enzymes that deactivate carcinogens in the body, enhancing our ability to eliminate carcinogens before they do any damage. Furthermore, in the laboratory onion and garlic compounds slow the growth and stimulate the self-destruction of cancer cells that form...studies show even greater reduction in cancer development from garlic and tomato than from either alone..."

The article mentions that some researchers now believe onions and garlic offer some protection from a wide variety of cancers, not merely specific types. This combined with the talk of stimulating enzymes seems to imply endogenous antioxidant stimulation.

Also this is the second recent article that mentions the beneficial cofactor effect of tomatoes. The other one was broccoli/tomato combo helping fight prostate cancer. Adding tomatoes, usually best in the form of a sauce with a bit of olive oil (more available antioxidants like lycopene) appears to enhance the preventative qualities.

More info on garlic and cancer is at the National Cancer Institute - from this a rather important part of to the preparation of garlic and it's ability to fight cancer "Peeling garlic releases an enzyme called allinase and starts a series of chemical reactions that produce diallyl disulfide (DADS). DADS is also formed when raw garlic is cut or crushed. However, if garlic is cooked immediately after peeling, the allinase is inactivated and the cancer-fighting benefit of DADS is lost. Scientists recommend waiting 15 minutes between peeling and cooking garlic to allow the allinase reaction to occur"

It also appears that processing garlic into powder and oils can also be beneficial in releasing and making more available anti-cancer compounds like "allin (responsible for the typical garlic odor), alline (odorless compound), ajoene (naturally occurring disulfide), diallyl sulfide (DAS), diallyl disulfide (DADS), diallyl trisulfide (DAT), S-allylcysteine (SAC), organosulfur compounds and allyl sulfur compounds"

Abstract from AJCN on some of the recent research

DogVitals antioxidant supplement for dogs