Quote from a textbook (Organic chemistry, Fourth Edition by Paula Yurkanis Bruice):
"A weaker base is a more electronegative base; that is, it is better able to accommodate its negative charge. Thus, weaker bases are better at withdrawing electrons inductively from the carbonyl carbon; electron withdrawal increases the carbonyl carbon’s susceptibility to nucleophilic attack."
Iodide is a weaker base than fluoride. So according to the textbook quote, iodide has a greater electron withdrawing ability than fluoride.
But the iodine atom is less electronegative than fluorine atom. How is it that the iodide ion is more electron withdrawing?