He had a plain but healthy diet: green peas and string beans from his garden, rice, barley water, lettuce, fish, brown bread, and baked potatoes twice a day.
Rockefeller’s most distinctive piece of medical advice—and the eternal bane of his dinner guests—was that people should chew each bite ten times before swallowing. So conscientiously did he adhere to this practice that he even advised people to chew liquids, which he would swirl around in his mouth. He would still be eating a half hour after other guests had finished. To promote digestion, he also thought it important to linger at the table for an hour or so after dinner.
The Enthusiast - The Life of John D. Rockefeller