T cells, which target infection and disease, can become more effective after a meal. The finding might help improve cancer-fighting therapies and optimize our response to vaccines An illustration of lymphocytes, or white blood cells in the immune system, which include T cells and other disease-fighting cells Ruslanas Baranauskas / Science Photo Library via Getty Images When you’ve felt under the weather, you may have received the old advice: “Feed a cold, starve a fever.” In certain ways, this adage isn’t true. No matter whether you have a fever or a cold, doctors advise drinking lots of fluids and maintaining good nutrition. The phrase has roots in an outdated idea that food can “warm” your body during a cold, and fasting can “cool it down” during a fever, as Lindsey Bever wrote for the Washington Post in February. It’s also not very clear—when you consider that a body fighting off illness can experience a fever and a cold at the same time , the saying’s meaning gets even more bungled.…