Peaches are a highly poisonous fruit, at least in the present-day. Whether or not this is a change from the Age of Legends is unknown, but at least one of the Forsaken has commented that they are "poisonous here and now."
This feature of peaches in the Third Age is based on the fact that the kernel of peaches in our own world contain chemicals called cyanogenic glycosides which, when broken down by the human body, release cyanide. This feature is also present in other fruits of the same family, such as apricots, plums, nectarines and cherries. Actual deaths have been reported through poisoning after eating these fruits when badly prepared. In the world of The Wheel of Time, peaches are meant to have evolved into something more deadly. Characters are often saying something is "... as certain as peaches are poison."