The more muscle mass you have the more energy you need while doing nothing. Look up base metabolic rate.
Lol I know BMR. But what I'm saying is most successful bbers take gear to maintain the muscle and eat a ton of protein, because you need aminos to support muscle mass. It would be counter-productive for someone to eat 800g carbs and 100g protein, when 300g protein and 500g carbs is probably more beneficial to someone who is sedentary most of the day (even at 250+lbs) because the goal is to keep as much muscle as possible while minimizing bodyfat. An endurance athlete can benefit way more from 1000g carbs/day and 100g protein because they don't care about maintaining muscle mass, they need energy for performance. Bodybuilders "perform" for an hour at the gym 5 days a week. Toss in 20mins steady-state cardio and you have Mr. O.
Protein is metabolized differently than carbs. It takes your body more energy to break down protein into aminos, use that for muscle repair, and then gluconeogenesis for what's left over than carbs going right into glucose and being used as energy that way. Plus, we have studies which show that food high in leucine (found in mostly eggs and meat) promote better muscle protein synthesis than things low or missing leucine such as most carbs sources.
Source:
http://jn.nutrition.org/content/136/2/533S.fullrecovery is apparently dependent on supplemental dietary leucine in order to increase the intracellular leucine concentration, which activates mTOR and the initiation factors eIF4E and eIF4G.
