Everytime I visit he plies me with food and drink,
It's just what Polish people do :)
The best way to deal with it is as follows:-
(a) When you know you are going to visit, don't eat anything 12 hours before you go.
(b) Don't say no to anything after you have had your fill, just say that you need a bit of time for it to digest, you'll have a bit more later.....
(c) When later turns up and you are asked again , just repeat (b) and say the food was very tasty and well made. Then just go home whenever it suits you lol.
Your Polish hosts will be content with the above :)