From the Souvenir Book of the 1957 IVU Congress in India, source unconfirmed:

FRIEDRICH NEITZSCHE; one of the world-great German philosophers. writes:
"All ancient philosophy was based on plain living. In this sense the few vegetarian philosophers have contributed more for the welfare of man than all the other philosophers together." (source not given)

- an extract from the diary of Cosima Wagner [wife of the composer Richard Wagner] - September 19, 1869:

Coffee with Prof. Nietzsche; unfortunately he vexes R.[ichard] very much with an oath he has sworn not to eat meat, but only vegetables. R. considers this nonsense, arrogance as well, and when the Prof. says it is morally important not to eat animals, etc., R. replies that our whole existence is a compromise, which we can only expiate by producing some good. One cannot do that just by drinking milk—better, then, to become an ascetic. To do good in our climate we need good nourishment, and so on. Since the Prof. admits that Richard is right, yet nevertheless sticks to his abstinence, R. becomes angry.

Within ten years Wagner had changed his mind and in 1880 published articles advocating vegetarianism - but by 1876 Nietzsche had fallen out with Wagner, and went the opposite way.... in 1882 Nietzsche published The Gay (=Merry) Science, in which a passage entitled Danger for Vegetarians stated:

A diet that consists predominantly of rice leads to the use of opium and narcotics, just as a diet that consists predominantly of potatoes leads to the use of liquor. But it also has subtler effects that include ways of thinking that have narcotic effects. This agrees with the fact that those who promote narcotic ways of thinking and feelings, like some Indian gurus, praise a diet that is entirely vegetarian and would like to impose that as a law upon the masses. In this way they want to create and increase the need that they are in a position to satisfy. [section 145. Translated by Walter Kaufmann].

By 1889 Nietzsche was suffering from a severe mental ilness, he died in 1900.