Don't skimp on food at a time like this!
I would say now is NOT the time to go for weight loss, which will further weaken you. Bear in mind that running is catabolic (breaks down tissue) rather than anabolic (builds muscle).
I actually GAINED 20 pounds in the course of training for my first marathon because I was foolish enough to pay attention to the running magazines and eat a diet high in carbohydrates, as well as using those miserable, sugar-laden sports drinks and bars.
After a long, hard slog, I have since succeeded (drum roll -- trumpet fanfare) in losing the weight, plus some more, by the simple expedient of eating lots of protein, fruit and vegetables, and ignoring every piece of so-called nutritional advice that's ever been published for runners. And I haven't gone near a sports drink in four years!
Unless you're running at elite pace, there's no need for high GI foods. But do be sure to get enough protein, because that will help build up what gets broken down when you train hard.
Hope this helps, and again, all the very best to you.
Beverly