When I was on pred the weight gain was always appreciated. I was about 30 pounds under weight. Now that I am at high school weight I am not sure that I would be quite so thrilled with it. High protein would probably be good due to its longer digestion times if you can stomach it. Stay away from light carbs though, they will just pack on the calories for you. As mentioned above, water can really help out with feeling full and not worrying about calories.