DNA methylation patterns change as individuals grow older, and DNA methylation appears susceptible to modification by the diet. Thus DNA methylation may be a mechanism through which diet can affect aging and longevity. We propose that effects on DNA methylation also contribute to the extension in lifespan observed in response to dietary restriction. Relationships between diet-induced changes in DNA methylation and parallel effects on aging and/or lifespan could, of course, be purely associative. Proof of these ideas requires experimental model systems in which it is possible to manipulate genome methylation status and to measure effects on aging and/or lifespan. Commonly-used short-lived and genetically-malleable metazoan species, such as Caenorhabditis elegans and Drosophila, are not suitable for such studies; the C. elegans genome is not methylated, and DNA methylation in Drosophila is dissimilar from mammalian DNA methylation, occurring at cytosines at sites other than in CpG sequences. The honeybee provides a potentially unique and tractable model for such studies. Female larval development into the long-lived queen phenotype or short-lived worker is determined purely by diet (royal jelly) through an effect on DNA methylation, and honeybee DNA methylation mirrors that of the mammalian genome. Mammalian cell lines and biochemical approaches offer complementary tools to address specific components of hypotheses relating to effects of diet on aging through DNA methylation in a more targeted manner. Our studies using mammalian cell lines are revealing effects of Sirt1 on DNA methylation, and indicate that Sirt1 and resveratrol affect the expression of different sets of genes.