I found in the following website
There has long been a rumor that Newton was vegetarian, although none of his biographies mention anything on the subject, so I wrote to his biographers to see if there was anything in the primary sources. I received this reply from Dr. Patricia Fara, a Newton scholar at Cambridge University: "I have heard the rumour, but the evidence suggests that he did eat meat except for the last five years of his life, when he was quite frail and followed a light diet which might perhaps have been vegetarian."
I have received the following note from the American Newton scholar Gale Christianson: "Newton did tend to eat vegetables and broth when he was an old man, but there is nothing to indicate that he was a conscious vegetarian...during the early and middle years."
Finally, James Gleick, the famous writer of 'Chaos' recently wrote a book about Newton. I asked him if he knew of the long-held rumor that he was vegetarian. He replied, "The 'rumor' started with his niece, who said he was reluctant to eat meat in later life. It's just one data point. Hardly anything is known about what he ate except that he didn't care much about meals."
So, it means that including Sir Isaac Newton's name in the group of vegetarians is not correct. I wish to know the truth