MINNEAPOLIS — John Steigauf spent more than a decade fiddling with the innards of those huge United Parcel Service trucks until an icy day two years ago when the company put him on leave from his mechanic’s job. A supervisor escorted him off the premises. His work was good. He hadn’t socked the boss or embezzled money. It had to do with what was inside him: diabetes. U.P.S. framed it as a safety issue: Mr. Steigauf’s blood sugar might suddenly plummet while he tested a truck, causing him to slam into someone. Mr. Steigauf considered it discrimination, a taint that diabetes can carry. ‘I was regarded as a damaged piece of meat,’ he said. ‘It was like, ‘You’re one of those, and we can’t have one of those.’ ‘ With 21 million American diabetics, disputes like this have increasingly rippled through the workplace: ¶A mortgage loan officer in Oregon was denied permission to eat at her desk to stanch her sugar fluctuations, and eventually was fired. ¶A Sears lingerie saleswoman in Illinois with nerve damage in her leg quit after being told she could not cut through a stockroom to reach her department. […]