Calorie restriction practitioners might find this piece from EurekAlert! (and the accompanying full text PDF) interesting: "The deterioration in immune function that occurs as an individual ages is thought to occur because the thymus involutes with age, causing a dramatic decrease in T cell output. New data [suggest] that in mice, thymic involution is caused by a decrease upon aging in thymic expression of both a hormone that is better known as a stimulator of food intake (ghrelin) and its receptor. ... harnessing this pathway might provide a new approach to boost immune function in individuals who are elderly or immunocompromised. ... infusion of ghrelin into old, but not young, mice markedly increased thymic mass, improved thymic architecture, and increased thymocyte and thymic epithelial cell numbers. These changes were associated with increased T cell output and increased diversity of the TCR repertoire of the peripheral T cell population. Consistent with these observations, age-associated thymic involution was accelerated in mice lacking either ghrelin or its receptor." It's far too early to be suggesting connections between the increased release of ghrelin with hunger and positive effects over the years of being hungry more often, but it is an intriguing line of thought.