When I was a destitute graduate student several years ago, I decided to earn a quick $75 by signing up for what sounded like a relatively innocuous clinical study. An I.V. in my left arm would feed precise amounts of glucose and insulin into my bloodstream, while from my right arm a nurse would periodically draw blood to test for glucose. The study would assess how effectively my body responded to sugar, a measure that predicts risk for developing type 2 diabetes.

As someone with a family history of the disease, I had long had a shapeless fear of it. A phone call from the nurse a few days later turned that vague anxiety into something much more concrete. The blood tests showed I was "insulin resistant," meaning that my muscle, fat, and liver cells were not responding to insulin as efficiently as they should--significantly boosting my risk of diabetes.