I was amused by his descriptions of his vegetarianism in his Autobiography. At 16, he decided to try a "vegetable diet," inspired by a book by someone named Tryon. In order to have more money to buy books, he saved money by eating lighter meals, like "a bisket [sic] or a slice of bread, a handful of raisins or a tart from the pastry-cook's, and a glass of water." He benefited from "that greater clearness of head and quicker apprehension which usually attend temperance in eating and drinking." Later he tried to convince Keimer, the printer for whom he worked, to adopt "the doctrine of using no animal food." Franklin deadpans, "He was usually a great glutton, and I promised myself some diversion in half starving him."
For some time, Franklin refrained from eating "animal food," following Tryon's teaching that eating meat is "unprovoked murder, since none of them had, or ever could do us any injury that might justify the slaughter." But one time, while very hungry at sea, some others on the ship were frying some fish, which "smelt admirably well." He began to waver, then remembered that "when the fish were opened, I saw smaller fish taken out of their stomachs; then thought I, 'If you eat one another, I don't see why we mayn't eat you.' So I din'd upon cod very heartily, and continued to eat with other people, returning only now and then occasionally to a vegetable diet."
Here follows one of the great justifications for doing whatever the heck you want: "So convenient a thing it is to be a reasonable creature, since it enables one to find or make a reason for everything one has a mind to do." Q.E.D.
What does all this have to do with running? Nothing.