Its about eating protein, but also enough carbs and fats, and the right kinds of carbs and fats.
So roughly, if he is an elite athlete training every day, he should be eating about 3200-3500 calories a day (for an average male, I think the RDI is about 2700 calories). This should translate to about 200-250g protein, 75-85g fat and 320-350g carbs, I think. He should try and keep the fats most mono and polyunsaturated. Since your body can only usefully process around 40g protein at a time, it is obvious that he should be eating at the very least 4 times a day with supplements. Getting enough rest is also important.
I got all this info from listening to a bodybuilding friend for a few hours, so I would assume that even a poor professional would know 1000 times more than me. Makes me then think that our F&C staff were either poor at communicating good practice to players, poor at/too lasy to individualise programs, soft on discipline, or that Fiora was soft on self-discipline.