Dr. William A. Alcott wrote about the beneficial aspects of a "Vegetable Diet" in 1838.  The book contains many testimonial letters from persons employing such a diet to cure various ailments.  In 1850, Alcott was a founding member and the first president of the American Vegetarian Society.  Louisa May Alcott was the daughter of his second cousin, Amos Bronson Alcott.

Dr. William A. Alcott  (1838)

"I have said, it was not my original intention to prove a vegetable and fruit diet to be anything more than safe.  But I wish not to be understood as entertaining, even at that time, any doubts in regard to the superiority of such a diet;  the only questions with me were, Whether the public mind was ready to hear and weigh the proofs, and Whether this volume was the place in which to present them.  Both these questions, however, as I went on, were settled, in the affirmative."