Its very important to intake more calories when starting an intense exercise training programme, the reason is simply because your body needs more energy. Depending on what type of fitness program your taking part with will determine how much energy you need to complete your fitness tasks?
Your training could be cardiovascular improvement (running) or muscular development (body building) you need to get more calories. When I say’’ get 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 vital clean energy, vitamins and minerals.
To figure out how many calories you need you first need to workout your weight in kilograms, you can do this simply by entering your weight into the google and converting the kg.
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12 stone in kg = 76.2035
Once you have your weight you then need on average 30 kcal per kg per day.
To find daily caloric needs, take 77 x 30 = 2310 calories.
During a fitness program add 100-300 kcals each day.
average fitness - 2410 Kcal
extreme fitness - 2610 Kcal
Of course the exact value changes depending on if you are awake and active or sleeping.
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