Its very important to intake more calories, when starting or during a training program you need more energy. Depending on what type of program you’re following weather it be cardio or muscular development you will need to intake more calories. When I say’’ intake more calories’’, this does not mean go to eat fast food with an high Kcal count, this means eating foods that are good for you and will provide you with energy, vitamins and minerals.
The GI index for food is used in the nutrition, this index will tell you how fast the transformation will take from carbohydrates into glucose.
For more information on GI check http://www.glycemicindex.com
To figure out the average intake you first you should find your weight in kilograms, to do this transform the weight in pounds ,easy divide by 2.2. You need on average 30 kcal per kg per day.
For example, if your weight is 140 pounds, weight in kilograms is 160/2.2 = 72.7 or 73 kg.
To find daily caloric needs, take 73 x 30 = 2190 calories.
During a fitness program add 100-300 kcals each day.
Of course the exact value changes depending on if you are awake and active or sleeping.