Question on ticket gates – can I walk through to get food then come back?

So the situation is – I get on SHINKANSEN in Tokyo to go to Nagoya. I get off SHINKANSEN in Nagoya and then immediately exit and buy tickets for the jr hida. Now I am stuck between gates but I meant to get food before boarding my next train. Can I input my tickets to exit the gate, then reuse them on my way in? Or will they be invalid