I would just go with whatever you are doing, I am not sure about changing your diet to try and change a blood test result like GD?
I would rather do I what I would normally do and the if it came up positive, then have a plan of action.
Changing your diet prior to the blood test will possibly not change the result at all.
I would think it would be better just to think about having a correct diet all the way through your pregnancy, then if the test comes up possible GD and subsequent tests show you have it, then it would be easier to mangage if you have already made those dietary adjustments.
Good luck with the tests.