|MadSci Network: Agricultural Sciences|
This is a good question. The answer is... yes and no.
Yes, you are peeling away many of the compounds which plants use as natural sunscreen, in the case of an apple, or to protect against soil bacteria, in the case of potatoes. These include carotenoids and flavonoids.
Even after you peel an apple or potato, there are plenty of nutrients left, but they are different from the ones contained in the skin.
Here is a website (the information is from the USDA, although this is not a
USDA website) that will let you and your Mom compare the changes in
nutrients for fruit with skin vs fruits without skin.
The bottom line is that it is generally best to eat a whole fruit or vegetables with the skin on, since you are getting both sets of nutrients (the ones in the skin and the one inside the fruit).
Finally, it is important to carefully wash the skin before eating it, and, of course, some fruit, like bananas, just taste better after peeling... :-)
I hope that this helps.
Try the links in the MadSci Library for more information on Agricultural Sciences.