Like most obsessions, it started benignly enough; like most modern antics, it began with an app.

“I started using My Fitness Pal a few years ago when I embarked on a health kick,” explains one thirty-something Londoner. “I was seriously exercising for the first time in my life, and wanted to track the calories I was burning while I ran. The app seemed like a really simple way to lose weight and avoid embarrassing and often demotivating Weight Watchers weigh-ins.”