The average American diet is actually too high in protein. Most people are in positive nitrogen retention... it doesn't take much protein to achieve positive nitrogen retention. Any protein consumed that is beyond the body's requirement will have to be either: converted to glucose through glycolysis to be burned off through activity or to be stored as glycogen or body fat.
Excess protein will not speed up muscle growth, it actually impedes it with the pleasant side effects of: increased body odor and bad breath, constipation, increased inflammation due to the immune system's reaction to the excess protein in the gut, and an impaired ability to recover between workouts.
The penis is not a muscle... people confuse the fact that the penis is made of smooth muscle cells with the skeletal muscle tissue that they think of as "muscles".
Smooth muscle tissue is found everywhere in the body and comprises the majority of tissue cells found in your organs. The veins and arteries are comprised entirely of smooth muscle cells. I highly doubt that most people think of their veins as "muscles".
The penis contains smooth muscle cells that are designed to produce an erection by enlarging and filling up with blood whenever the required chemical reaction is initiated.
That is fucking it... when you flex your penis you are putting tension on a muscle in your pelvis that is attached to a tendon that can lift your penis up and make it "strong". The powerful pelvic floor can also initiated by squeezing the PC muscles and sending increased blood flowing to the penis which can be quickly absorbed by the smooth muscle cells if they are in a state of expansion (dilated by nitric oxide gas).
There is no skeletal muscle in the penis, only smooth muscle cells. Increased protein would have no effect on one's penis size.
The theory that it would is based on the theoretical notion that the OP is deficient in protein. if he was deficient in protein... yes an increase in protein will make every system of his body run better (including erections), but that would ONLY TAKE PLACE IF HE WAS DEFICIENT IN PROTEIN in the first place.
Seeing that one doesn't need to eat but a couple of cans of tuna a day to meet their protein needs... I am gonna say that protein or weight gain shakes will do nothing to increase one's penis size. Weight gain powders contain huge amounts of rapidly dissolving macro nutrients that can easily be converted to bodyfat and can also increase inflammation throughout the body. This can result in a puffy appearance (holding water under your skin but not under your penis! lolz!) and one could even experience a gain in bodyfat which can seriously make one's penis look visually small.
I didn't want to have to wade into this, but I thought that it was time. :wink: