Imagine getting a call from your doctor if you let your gym membership lapse, make a habit of buying candy bars at the checkout counter, or begin shopping at plus-size clothing stores. For patients of Carolinas HealthCare System, which operates the largest group of medical centers in North and South Carolina, such a day could be sooner than they think. Carolinas HealthCare, which runs more than 900 care centers, including hospitals, nursing homes, doctors’ offices, and surgical centers, has begun plugging consumer data on 2 million people into algorithms designed to identify high-risk patients so that doctors can intervene before they get sick. The company purchases the data from brokers who cull public records, store loyalty program transactions, and credit card purchases.