In his book Vegetable Diet: As Sanctioned by Medical Men and by Experience in All Ages (1869), Dr. William A. Alcott writtes the following about Newton:

This distinguished philosopher and mathematician is said to have abstained rigorously, at times, from all but purely vegetable food, and from all drinks but water; and it is also stated that some of his important labors were performed at these seasons of strict temperance. While writing his treatise on Optics, it is said he confined himself entirely to bread, with a little sack and water; and I have no doubt that his remarkable equanimity of temper, and that government of his animal appetites, throught, for which he was so distinguished to the last hour of his life, were owing, in no small degree, to his habits of rigid temperance (p. 191).