I think given the circumstances you should do whatever it is your body needs to get you through this. If you have to eat a bagel so you won't get ill and lose precious disease fighting weight, than so be it. Your health and the ability to fight off the radiation is most important. If you're 10 pounds heavier when fiinished, so be it. As long as you're eating healthy, good carbs, I wouldn't stress at all!

Best of luck, a good friend of mine just went through this about 2 months ago and she is doing WONDERFULLY!