Humblejumbo,
I don't think masturbation reduces the size of the penis as much as poor diet and lack of testosterone does. In fact, Jelqing, vaccuum pumping, stretching, and hanging are all forms of masturbation and these are known ways to make the penis grow. Jelqing is like masturbation in that you stroke your cock with lube and it pushes blood into the penis which helps girth.
Another cause of small penises is lack of blood circulation. Wearing tight pants, having lots of fat in the fat pad, or possibly even smoking can cause the penis to shrink because you wouldn't be able to be erect. Yes, being horny DOES help penile growth because of blood constantly entering the penis when you get erect for a hot girl or guy. Being bi gives you more chances to have erections because you don't discriminate between a hot guy or hot girl. That is why masturbation helps. Prudes or church folks have smaller penises because they never use them or some may even cut them off. (They may quote, "If the eye offends thee pluck them out! If the penis offends thee, cut it off!)
My post against soy products is through my personal experiences and by observing people who are in my Chinese culture, then putting 2 and 2 together. Also there are articles stating that soy produces estrogen such as these:
Convincing evidence that at dietary levels, the estrogens found in soy do not stimulate cell growth and other markers for cancer risk
estrogen/ men
Estrogen is the culprit to the decrease in sperm count and penile size. The population in Japan is much smaller than that of the US and they are the Asian men that consume soy on a daily basis. Now to explain the Chinese population, the Chinese do not consume soy daily and they have summers where soy spoils and they avoid it like a disease and they copulate then. Japan, can eat soy all year around because their weather is cloudy and soy can be kept in Japanese environment. They have much less birth rate success than Asian men of other Asian races.
I have produced evidence supporting my conclusion and observation against soy products. If you like soy however, you better be a woman or be prepared to have a small dick.