Someone told me (can't remember who) that there are a two simple "rules" to think of when it comes to fruit and veggies.
For veggies, if the part that you eat grows below ground, be careful. If the part you eat grows above ground, go for it. The chives and onions case fits this.
For fruit, the more sun/heat a fruit needs to grow the more sugar it contains and the less you should eat. Example, apples are okay, grapes are worse, pineapples and bananas are worse still.
Don't know how accurate these "rules" are, but they are what I use to decide what I will eat till it is coming out my ears, and what I will avoid.
Steve