From my experience every 5000 steps burns about 250 calories (obviously varies based on speed, weight, etc) but lets assume this is the case for you. So just to keep at the same level of calorie balance, you would have to eat 250-400 extra calories a day. at the end of the day it comes down to what your surplus/deficit is compared to maintenance, and if your maintenace increased due to higher expenditure, it is in fact necessary to eat more.