This is your brain on sugar—for real. Scientists have used imaging tests to show for the first time that fructose, a sugar that saturates the American diet, can trigger brain changes that may lead to overeating. After drinking a fructose beverage, the brain doesn’t register the feeling of being full as it does when simple glucose is consumed, researchers found. It’s a small study and does not prove that fructose or its relative, high-fructose corn syrup, can cause obesity, but experts say it adds evidence they may play a role. These sugars often are added to processed foods and beverages,...