If you are looking for significant gains in muscle mass, you need to be in an ‘anabolic state’. This involves consuming more calories than you are burning. Protein (amino acids), particularly leucine, isoleucine, valine and glutamine, are extremely important in providing the building blocks for new muscle synthesis. For muscle growth, aim for 1.2g-1.7kg of protein per kilo of body weight, consumed evenly across the entire day. Any more than this has been shown to be both unnecessary and expensive!
Carbohydrates are equally as important. They provide the energy needed to maintain the heavy resistance training required for muscle growth. Without carbohydrate (at meals and either before and/or after the session), recovery becomes sub-optimal and strength decreases whilst an anabolic state cannot be maintained.