We do not know how exactly it happened, but poor John Doe made a space-time trip along a three dimensional analog of a Möbius strip (a Klein bottle). He is now back on Earth, but he is now the mirror image of his former self: His heart beats on the right side, he is left-handed now, and even worse: All the molecules in his body (peptides, sugars, DNA and RNA) are mirrored, too.
Water is still drinkable and air is still breathable, but all the food on Earth is inedible or even poisonous to him.
Scientists quickly diagnose and confirm John's state, but how can he be fed?
I am asking about a plan to prepare food for him, not only noticing the fact that normal food is not available for him and he's in trouble. That I know already.
To be realistic, any programme to feed poor John Doe must be set up in reasonable time before he dies of starvation. You may use mirror bacteria extracted from John's skin or from John intestinal tract.
Doing the space-time trip again or going back the way he has gone is unfortunately not an option.