Not long ago, I watched a woman set a carton of Land O’ Lakes Fat-Free Half-and-Half on the conveyor belt at a supermarket. “Can I ask you why you’re buying fat-free half-and-half?” I said. Half-and-half is defined by its fat content: about 10 percent, more than milk, less than cream.“Because it’s fat-free?” she responded.“Do you know what they replace the fat with?” I asked.“Hmm,” she said, then lifted the carton and read the second ingredient on the label after skim milk: “Corn syrup.” She frowned at me. Then she set the carton back on the conveyor belt to be scanned along with the rest of her groceries...