Ryan Crownholm, a middle-aged Army veteran with luminous green eyes and a strong jawline, likes to describe himself as a health hacker. He has written on LinkedIn that, after founding and running several construction-related companies, he started to think of his own body as a data source. During the pandemic, he attached a continuous glucose monitor to his skin, bought an Oura ring to monitor his sleep, and signed up for a healthy meal-delivery service.