India, Sept. 1 -- A few months ago, in a running group in Cupertino, I was jogging with humans who wore digital watches and iPhones to calculate their pace, heartbeat, gait, movement, and blood pressure. This mass of data, one of the runners told me later, was something that helped him improve his efficiency, making him a better runner, avoiding injury, and increasing the performance of his body. This friendly runner, who worked in one of the Big Tech companies, reminded me of someone else in technology who has turned tracking his body into a billion-dollar empire.

Bryan Johnson, an American billionaire, made his money in 2013 when he sold his company. Since 2021, he has made collecting data about his body an art form with Project Bluepr...