[QUOTE]Haha. I'm a little against supplements because I believe if you take care of yourself, you dont need them.[/QUOTE]
This is true provided your not doing a lot of exercising, whether it's running or weight lifting. The more active you are the more nutrients your body needs. In order to get these nutrients you need to either eat more or take supplements. If your trying to maintain or loose weight eating more isn't a good alternative. If you doing cross country you don't want to put on weight, unless your under weight.
A low carb diet isn't what you want since you do need the carbs for energy. You need to find your resting metabolic rate(RMR) and your daily caloric needs. I take it your in high school. So your 14-15? At 5'3"/ 113lbs your not under weight. Your body mass index is 20, at 19.1 you are considered under weight and 27.3 is over weight. Your RMR is about 1372 and your daily caloric needs will be about 2399 with the amount of running and cardio you will be doing for cross country. If the number of calories you take in each day minus what you burn equals 2399 or in that range you will maintain about the same weight. If it is more you will gain weight and vise versa. So it depends on what you want to do. Regardless of if you want your weight to go up, down or stay the same you have to eat healthier. My experience has been eating 5 times a day is much better than three times a day. This would be three decent, healthy meals with two snacks in between separated by about 3 hours. This will help keep your blood sugar levels in a healthy range so your body doesn't start taking it's nutrients from your lean muscle.
The only way to prepare for a lot of running is to run a lot. You can do other cardio exercises to help with endurance but you need to run in order to condition your body for running. Here is the schedule i used when i started regular weekly training.
WEEKS #1, 2: 2 miles/day, 8:30 pace, M/W/F (6 miles/week)
WEEK #3: No running. High risk of stress fractures.
WEEK #4: 3 miles/day, M/W/F (9 miles/wk)
WEEKS #5, 6: 2/3/4/2 miles, M/Tu/Th/F (11 miles/wk)
WEEKS #7, 8: 3/4/5/2 miles, M/Tu/Th/F (14 miles/wk)
WEEK #9: same as #7, 8 (14 miles/wk)
There is a second part for the run but it shouldn't be started until you can do 14 miles a week. Hope this helps.