hey grninja, I have been a competitive swimmer for most of my life (Up to national level, but never took it seriously silly me), I can honestly say I have never ever indulged in anything other than eat what I want..., I am no longer competing,. only becuase i just dont have the time, but I still swim most days, twice heavily with the club and I play squash and dance in addition. i have always been well built, family trait, but never fat, although tummy a bit bigger than it should be these days....if i was really interested in toning up then I would eat more protein....to lose weight not to gain it....
If you want to gain you dont need just protein you need fats and carbs....I assume you are eating these too. I may be out of touch as i havent looked at this for nigh on 20 years but this is how i remember it...
as regards muscle mass, not power, the only way recognised is by working them and in extreme cases to expand them by damaging the muscles, ie creating rips in the muscle by overworking them, causing real pain....this is very extreme....but it then causes the body to repair the damage and by doing so it increases the muscle mass....but the muscles pound for pound are shite in reality....but you will grow...eating regularly is based on the notion that if your body is in need of energy it will take this from its resources...ie it will eat your body...weight loss occurs...now if you have no fat it will take that energy from somewhere else....ie your muscles so all that hard work the day before is destroyed....therefore its important to eat plnety of calories...
You need a full diet, one thats meets all your energy needs, fats and carbs...very important that fats are included....and one that meets your body building needs, ie proteins but do niot forget all of the other minerals and vitamins that will be needed as well....it is supposed to be better for us to eat regularly and often so there is no harm in that just make sure you eat enough of the normal stuff...real meat with the fat, bread, potatoes, eggs but not too many....one a day unless you really are going for it...more are bad for your healt in other ways...you need to be sure you are keeping your choleterol levels very very low because these types of diets can increase levels to dangerous levels and cause blocked arteries and heart attacks in later life.....be aware that there are consequences to changing your natural body shape....especially as you get older...and your body will revert to its natural size once you stop due to injury, age, or lack of focus....something we are all prone to......
On a final note, If you really want to bulk then get hold of some steriods for a short period....they will bulk you within 12 months, but you will noitce a big difference within 4 weeks, makes you impotent and highly aggressive...so proceed with caution...but it certainly works...
If I was actually giving real advice and I am not but for what its worth I would find a physical sport that meets your needs and use that as your target not just body mass increases...