That was probably an old wives’ tale in the first place.

“I don’t think it was ever valid” to tell people to wait an hour to swim, said William Evans, director of the nutrition, metabolism and exercise laboratory at the University of Arkansas for Medical Sciences. People used to think that perhaps all the blood flowing to the gut for digestion would cause muscles to cramp up, he added. “But that doesn’t really happen. People can run long distances on a full stomach.