Carbs are normally 4 calories per gram but fibre as a carbohydrate is not completely digested by the body so estimate is 2 calories per gram. zero. Your body doesn't have the enzymes to digest fiber Some fibre is soluble and can be digested so this answer above is not correct. Carbs are normally 4 calories per gram but fibre as a carbohydrate is not completely digested by the body so estimate is 2 calories per gram.