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.
This was expanded by Nietzsche's sister Elizabeth in The Nietzsche-Wagner correspondence (PDF 9mb) edited by Elizabeth, pub. London 1922. p.45, the Chapter headed 'Experiences during the Winter of 1870':
My brother was also
very fond of the children and was regaled with a new
assortment of children's stories each time he went to
Tribschen. Little Eva [Wagner's youngest daughter], in particular, was fond of making
up all sorts of stories about the "good Herr Nützsche."
Sometimes she called him the "Good Herr Fressor" a name
which always brought forth a reproof from Isolde [the next oldest] who insisted
that it was "Professor, not Fressor; he is not going
to eat anyone!" (The point of this little story is entirely
lost in English as the emphasis lies on the word "fressen"
"to eat" which is only used when applied to animals.)
Eva also took the greatest interest in my brother's physical
well-being and was very much concerned that there was "never any meat on the good Herr Nü-tzsche's plate."
Both Wagner and Frau Cosima made strenuous efforts to
convert my brother from the vegetarian diet to which he was
addicted, and, in time, he did abandon this, whether out of
love of Wagner, or of little Eva, I cannot say.
Elizabeth's view of vegetarianism as an addiction gives an insight into the blinkered thinking of the time....
In late 1874 Cosima Wagner wrote to Nietzsche congratulating him on his book about Schopenhauer, including: "your wonderful
picture of the relationship existing between animals
and men" (p.231 of the above correspondence). There seemed to be some convergence of thinking at this point, and the tone of the letter implies that Nietzsche was still vegetarian at this point, though it is not at all clear.
By 1875 Wagner had changed his mind, telling dinner guests he wanted to be vegetarian but his physician wouldn't allow it, and in 1880 published articles advocating vegetarianism.
Meanwhile, in the summer of 1875 Nietzsche consulted a Dr. Wiel about various health problems. In 'The Young Niezsche' p.338, his sister Elizabeth gives the following account:
He wrote to Gersdorff concerning his state of health as
follows : " My trouble has been diagnosed as chronic
gastric catarrh, accompanied by great dilatation of the
stomach. This dilatation causes vascular engorgements,
and results in the brain being insufficiently supplied with
blood. In the first place, then, the stomach is to be
reduced to its normal size, by means of an extraordinary
diet consisting of the most nourishing substances, provided
that they be not bulky, i.e., almost exclusively meat. In
addition I am to take Carlsbad salts, and am to have
leeches applied to my head."
Then in later letters to his friends he goes on to say : " In my last letter I told you how I felt ; meanwhile, however,
the diet has been changed. At my request I am now
eating much less ; I am weary of eating so much meat...."
Cearly Nietzsche's vegetarianism had ended by this time, and he continued eating meat. His health seemed to improve for a while, but declined again after a few months. In 1876 Nietzsche fell out with Wagner and began to turn against him.
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 illness, he died in 1900.