Oldfield was senior physician to the Lady Margaret Fruitarian Hospital in Bromley, which he founded in 1903. He was a member of the Fruitarian Society whose members lived on "the produce of harvest field, garden, forest and orchard, with milk, butter, cheese, eggs and honey". No alcohol, fish or meat was permitted at the Lady Margaret Fruitarian Hospital. The food was cooked in coconut oil. Oldfield also founded the fruitarian Margaret Manor hospital in Doddington, Kent. His type of fruitarian diet was not a strict type of fruitarianism. A reviewer in 1909, noted that "as fruitarian dietary includes milk, butter, eggs, cheese, and honey, along with fruits, nuts, and vegetables, healthy existence is quite possible for Dr Oldfield and his followers." A recipe of his "Margaret Plum Pudding" was included in Cecilia Maria de Candia's cookbook, The Kitchen Garden and the Cook. Oldfield was not a vegan, as he consumed dairy products and eggs. He recommended a daily diet of dandelion leaves, eggs, grapes, honey, lettuce, milk, salad, and watercress. In 1931, he commented that "I am proud to say that the only point on which we of the Fruitarian Society disagree with Mr. Gandhi is that Mr. Gandhi will not eat eggs, because they contain Life." Oldfield was President of the West London Food Reform Society, a vegetarian group based in Bayswater, founded in 1891. Edwin Arnold was vice-President and Gandhi was Secretary. He was associated with the London Vegetarian Society and editor for their publication, The Vegetarian. Oldfield was also the secretary of the Vegetarian Federal Union. He was a member of the Order of the Golden Age and the Humanitarian League. Oldfield authored the entry "Vegetarianism," for the Encyclopædia Britannica. Oldfield did not identify as a vegetarian. He stated that "I object absolutely to vegetarianism, because the word smacks of onions and cabbage. It gives people the idea that you live on watercress and browse on odds and ends of garbage." He substituted the word fruitarianism for vegetarianism, which was controversial. The Vegetarian Society were in disagreement with Oldfield’s assertions.
Religious beliefs
In 1891, Oldfield attempted to convert Gandhi to the Anglican faith and urged him to read the Bible. However, by the 20th century he had changed his faith. In 1904, he commented that "as a medical man, seeing much of pain and suffering and dying, my experience does not lead me to think that it is the profession of the Christian creed which is by any means the sole method of securing happiness of soul in this world, or which removes the fear of passing on to the next." Oldfield concluded that a "wider conception of God" was needed. Oldfield is listed in A Biographical Dictionary of Modern Rationalists as a theist with mystic ideas about the soul.
Selected publications
The Penalty of Death: Or, the Problem of Capital Punishment
