Garlic

I chew a clove of garlic and wash it down with water.  If you peel a clove and let it sit or even refrigerate it, it begins to lose the allicin within about 10 minutes and if it sits over night the allicin is gone.  The allicin is what is believed to give garlic it health benefits.  Do not mix garlic and oil and store it that way because if there is any fungus on the garlic, it can grow while in the oil and create enough poison to kill you (and has done so).

Heating and cooking garlic also causes it to loose its allicin, so raw is best.  However, the Japanese have done a lot of university level research regarding the health benefits of garlic and have produced a super garlic that they age and encapsulate in a product called Kyolic.  It is expensive for what you get, but supposedly has lots of benefits.  There are also other high allicin garlics such as Pur-Gar and there are arguments for both kinds.  I prefer mine raw, though I do include it in cooking when I can.