If you knew a month ahead of time that you would be in a situation with little to no food for 3-4 weeks, should you prepare your body by changing your caloric intake?
I would prepare my body by leaving and going to where the food is!
Okay, now that I have that out of my system, I'd say that you're better off dieting beforehand so that your body and mind are more used to working with less calories. I'd also say that you should consult a doctor before doing any such thing.