Any nutritionist who tells you to simply be concerned with the number of calories you are consuming as you try to lose weight should be discarded immediately. The body does not treat all foods the same and depriving your body of calories can lead to muscle loss instead of fat loss. If you lose muscle, you slow your metabolic rate. To make it simple, think of your metabolic rate as the rate which you can "burn through" food. If you have more muscle, your metabolic rate is higher and vice versa.
The 3 main macronutrients are carbohydrates, proteins and fats. Your body burns or processes each one differently. For example, if you eat the macronutrient Fat, your body burns about 5% of the calories consumed to process digestion. If you eat the macronutrient Carbohydrates, your body burns about 10% of the calories to digest the food. And, if you eat the macronutrient Protein, your body burns 15 to 20% of the calories consumed to simply digest the food. In other words, more energy is required to break down protein than carbohydrates and fats.
But you need to eat all 3 macronutrients to get the most results as you try to sculpt a hard body. Your carbohydrate intake should never be more than the amount your muscles and liver can store. Anything over that amount and the excess carbs will most likely be stored as body fat. What amount of carbs is a good amount to eat and not have fat storage? There is no exact answer. But if you will keep your portions small (like 1 gram of carbs for every pound of body weight per day), and avoid simple sugar like the plague, you will pretty much assure yourself that you are not storing carbs as body fat.
Keep in mind that muscle tissue is very easy to break down. If you are void of stored carbs (glycogen) in the muscles, amino acids can be broken down and converted to glucose for energy. A simple way to understand this is to remember that during intense weight training, a lack of carbs forces your body to break down muscle to supply energy. Because of this, your two biggest carbs meals of the day could be the meal before your resistance training workout and the meal after your resistance training workout.
But be sure to keep your protein intake high throughout the day and try to get your protein from real food as much as possible. Try to get at least a gram of protein for every pound of body weight, spread out over 5 to 6 meals per day. Remember that whey protein shakes burn through your body very quickly (90 minutes), so if you must drink protein shakes a lot due to your schedule, be sure to get a blend of Whey, Casein and/or Egg protein so you will have a steady supply for more than 90 minutes.