from Raga Mala, the autobiography of Ravi Shankar, published in 1997:
Dick Bock had often spoken to me about John Coltrane over the previous few years: about how he was a fan of mine, and had all my records. At some point during the winter of 1964-65, when I was back in America giving something like forty-two recitals on another coast-to-coast tour . . . Dick brought him to meet me in New York.
. . . When John Coltrane came to me, he looked different from his contemporaries: so clean, well-mannered and humble. About six months earlier he had apparently given up drugs and drink, become a vegetarian and taken to reading Ramakrishna's book's. For a jazz musician to go to the other extreme, especially in those days, was a pleasant surprise.
. . . We met again next time I came to New York, for a short tour in 1966, when we fixed a date the following year for him to come to LA for a few weeks to learn properly from me. Sadly he died before then.
the accounts below show that 'six months earlier' should have been six years earlier....
an online biography suggests this was over a longer period:
Following his release from the Miles Davis Quintet in 1956, Coltrane experienced a period of depression, followed by what he called "a spiritual awakening". Following intense meditation and prayer, Coltrane gave up drinking, smoking, and his destructive drug habit. During the seven-year period from 1957 to 1964, Coltrane began to become interested in nonwestern music and philosophy. He explored West African music as well as the music of India. Though he had considered himself a Christian all his life, he began to read books about Hinduism, Islam, science, astrology, yoga, and African history.
He began to have dreams in which he believed that God revealed various musical works and concepts to him. In the winter of 1964, A Love Supreme was revealed to Coltrane, in its entirety, through such a dream. He and his quartet recorded the work in December of 1964 in the same order that the tracks are programmed on the recording.
Apparently the cover of the album stated that Coltrane was a vegetarian.
from 'As Serious as Yout Life - the story of the new jazz' by Valerie Wilmer, 1977:
In addition to his musical importance, Coltrane exerted a profound spiritual influence on the musicians who followed in his footsteps. He was, according to all accounts, a modest man involved in a continual search for new areas of self-expression, andhe projected a personal quality that younger musicians have drawn on and used asa model for their own behaviour.
[chapter on Sun Ra]. . . It was during this period  that John Coltrane was playing with Miles Davis. Pat Patrick introduced the saxophonist to him [Sun Ra who was vegetarian at that time]. According to John Gilmore, Coltrane had not yet formulated the style he was searching for. He was exposed to Sun Ra's poetry and philosophy as well as his music, and things started falling into place for him. As a result of reading Sun Ra's literature, he managed to break a heavy drug habit, and three months after taking the Arkestra's [Sun Ra's band] records to study, he left Davis and started to take a new direction in both his musical and personal life. Coltrane was not alone; several notable players have been helped straighten their tangled lives and kick their addiction through the pianists's wisdom.
John Coltrane's spiritual conversion and subsequent adoption of a vegetarian diet surely extended his life. This positive change in the late 1950s was, perhaps, not enough to counter two high risk factors for liver cancer: his alcohol and heroin abuse through the 1940s and early 1950s.
from Nuno Metello
François Postif wrote the following in the preface to a 1961
"John Coltrane is on a diet, and, what's more, a bit of a vegetarian.
[…] John picked here and there some leaves of lettuce, some hazel
nuts, and cracked an egg to eat at his seat. […] I met him later,
affable and relaxed, in his room at the Claridge Hotel, busy
squeezing some oranges and eating some leaves of lettuce." (Quoted in
Lewis Porter, John Coltrane, His Life and Music, The University of
Michigan Press, p. 253)
He used to have tomato juice and raw eggs for breakfast. According to
"He tucked into a slightly bizarre dinner of two raw egg yolks, clear
soup, milk, iced water and fresh peaches." (Porter, p. 254)
Valerie Wilmer wrote:
"He told me he had adopted a vegetarian diet and wanted to eat some
fruit before getting early night." (Porter, p. 254)
see also Alice Coltrane; Sun Ra; Ornette Coleman