Not GP, but presumably it's a reference to the fact that (white) rice and (refined) pasta are processed in a way that makes them tastier but not as healthy. While you can eat brown rice and whole wheat pasta, they are quite a bit less common, and not as tasty.
Yeah, pick your poison. I've seen Prop 65 warnings on spinach, which apparently absorbs quite a bit of heavy metals from the soil. Eat your vegetables, but not too much!
"Eat cells, not substances" is a somewhat similar rule to "limit processed food intake", but the former would seem to encourage both pasta and rice while the latter would discourage pasta if you're being strict about it and rice if you're being extremely strict.
At some point I predict the endogenous pesticides in plants are going to be found to be very problematic. The famous Ames Test for mutagens goes off on them.
> Plants have evolved a variety of pesticides and antifeedant compounds, many of which are reactive and toxic at some level - therefore, most (as in 99.99%, according to his estimate) of the pesticides in the human diet are those found in the plants themselves. The cruciferous vegetables (broccoli, cabbage, mustard and so on) are particularly rich in compounds that will light up an Ames test. A fine article of his from 1990 (Ang. Chem. Int. Ed.,29, 1197) states that ". . .it is probably true that almost every plant product in the supermarket contains natural carcinogens."