I think it depends on which nutrients you're trying to actually substitute. Fructose seems to have different effects on insulin and digestion than the starches you might find in a potato, and vitamins can break down when cooked so fruits might be a better source than vegetables which are usually cooked.
This is a thread where people can ask questions that they would ordinarily feel embarrassed for not knowing the answer to. The previous "stupid" questions thread is at almost 500 questions in about a month, so I think it's time for a new one.
Also, I have a new "stupid" question.