Ai Weiwei, one of China's best-known contemporary artists, over the weekend posted his first updates to Twitter since being released from government detention.

Mr. Ai, who has more than 95,000 followers on the microblogging service, tweeted a handful of times through Sunday. "Ten dumplings for lunch, regained three kilos," he wrote, followed by Instagram photos of himself peering into the camera and another of his feet on a scale that read 214 pounds ("Ai weigh weigh!" quipped one follower).

He...