Stick with carbs that are lower on the glycemic scale. You CAN lose while training for a marathon. But I would focus more on fat loss, so you will lean down (lose fat/inches). Get plenty of protein, fruit, vegetables, Greek yogurt and cheese sticks are great. You might try counting calories and play around with them to see what helps you lose (if you aren't already). Strength training a few times a week can also help you (it helps you with the running as well). Jillian Michaels has a new one called "Beginner Shred" which is a great way of getting in to it (if you don't already). And it's short. Good luck!