We can begin by rewriting the sentence in a more convenient way:
"If I don't eat too much, I'll exercise."
The phrase speaks about an action (exercise) that is going to be done provided a condition is fulfilled (don't eat too much) This is a conditional.
p = I eat too much
~p = I don't eat too much.
Then, if ~p happens, then q will happen
We can write this as
~p->q
With this, the correct answer is option D.