For bodybuilding purposes, I recommend aiming for the following food percentages: Protein - 40%, Carbohydrates - 40%, and Fat - 20%. This is very flexible depending on your goals. I would use this balance for gaining weight. A contest diet would be much higher in protein, for example. It also depends on your body type (i.e. you tend to gain/lose weight easily, or have a fast/slow metabolism). But make no mistake, protein intake is very important to building muscle. It simply can't be done without adequate amounts. The general rule of thumb seems to be: eat 1 to 1.5 grams of protein per pound of body weight. So, if you're 150 pounds, try to eat between 150 and 225 grams of protein a day.
The body can typically only digest 40 grams of protein at any one sitting. I recommend distributing your protein intake over the entire day in the form of whole foods and protein supplements. For example, if you eat 6 small meals a day (like most bodybuilders) then try to consume 30-40 grams of protein per meal. More if you're a big person, and less if you're small. The goal is to provide your body with a constant stream of protein to rebuild muscle. That way, every time your body goes to repair a damaged muscle fiber there will be raw materials available.
A day's meal plan may look like this:
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