ScienCentral looks at recent research into the beneficial effects of calorie restriction on the aging immune system: "when we say caloric restriction we typically mean ... taking about a third fewer calories, or about 30 percent [of] calories, compared to what you would take if you had no dietary restriction at all. And ... not only do animals live longer under this treatment, but also they're much, much healthier. They don't seem to be showing many of the diseases characteristic of old age. ... monkeys on caloric restriction had significantly stronger immune systems. They had more immune cells overall, and, most significantly, had more of a valuable type of immune cell called a naive T cell. Most naive T cells are created early in life. Once they get called into action to fight a specific pathogen, they turn into 'memory T cells' that are only capable of fighting that specific pathogen. But naive T cells are capable of attacking any pathogen, including ones the body has never encountered. ... As we use this naive T cell reserve, we're less and less really prepared to fend off new pathogens."