According to the Geneva Convention, what must a nation do to Prisoners of War if it doesn't have enough food for them?

During wars food is often in short supply, for both civilians and military members. What does the Geneva Convention suggest countries should do if there aren't enough food supplies for Prisoners of War? Should they be released? And what should the country do about future prisoners of war - simply refuse them the right to surrender?

The question is inspired by Ukraine's struggle to secure enough food for its cities during the current conflict.