You don't need a synonym - you could just omit the phrase altogether:
the number of people who preferred fast food restaurants in France outnumbered that of those who prefer home-cooked food in Italy.
The use of the word 'outnumbered' already implies that the two things being compared are numbers, or counts, so no need at all to state that they are numbers.
Make sure your verbs are in the correct tense - you say "outnumbered", so you must be basing this on data that was collected in the past, but you have used both "preferred" and "prefer". All of these ideally should be in the same tense.