insulin is a hormone secreted by the pancrease which stores body fat and lowers blood sugar levels.....when you eat carbohydrates as they are burned they degrade down to different sugars....so if you eat low gi carbs like oatmeal that digest slowly your blood sugar level stays relatively low and constant there for an insulin release response doesnt occur and there for that non existant hormone isnt around to store fat...where as if you eat a candy bar (high gi) which will raise blood sugar levels dramatically in a short period of time you will receive and insulin spike and the fat storing hormone will be shot into your blood...........
inside your muscle there are stores of glycogen which is basically your muscles energy.....after your workouts you eat carbs to replenish these stores...thats also why doing cardio after a weight workout is more benficial as these stores or energy are depleted therefore your body will dip into fat stores to complete the cardio
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