The low hanging fruit in genetics research has mostly been harvested, and now the work of studying genes as part of systems biology is well underway. Metabolism and nutrition seem to be an ideal complex system in which to apply the knowledge and methods of genetics and genomics. Diet is perhaps the most important environmental factor we are exposed to. Nutritional factors are thought to be the cause of 30–60% of cancers (similar in magnitude to smoking; Doll, 1992), diabetes is a nutritional/metabolic disorder, we are all familiar with the cholesterol–cardiovascular disease relationship, and obesity is a pressing nutritional problem, with a majority of Americans overweight and expanding rapidly (Ogden et al., 2007). If genetic scientists are looking for a complex system to step up to and address, what better choice? Hence, the developing discipline of nutrigenomics.