There is a good article in the nautilus website, at
about hormesis and oxidative stress.
I've been trying to add a question to open the article to discussion but apparently it kept getting deleted...
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Yes, a nice unusually sensationalist title to it, but it's quite true. Plants don't produce vitamins or macronutrients, for our use, they produce them for their own needs. A lot of what they make are countermeasures to being eaten by insects. We've developed the ability to use what they make for our own benefit.
For example, if you feed garlic to cats or dogs, or chocolate, you'll make them very sick if not kill them. But we have the proper detox mechanisms to process these plants, and even benefit from them.
There's an interesting effect where if you take vitamin C in small amounts, it's an antioxidant, but if you take it in large amounts, it's an oxidant and can be used to kill infections and such.