Diet and chronic disease relationships are complex. Nutrient deficiency diseases, such as scurvy, can be cured by consumption of a missing nutrient, for example, vitamin C. In contrast, chronic disease incidence is linked to a wide range of nutrient exposures, energy, fats, sodium, dietary fiber; and food exposures, whole grains, vegetables, nuts, and so on, making it challenging to set a clear direction on dietary guidance. Additionally, nondietary factors including exercise, stress, smoking, and other environmental exposures are linked to chronic disease incidence. Since 1980, the US government has issued Dietary Guidelines for Americans every 5 years. These recommendations are intended for healthy Americans 2 years or older. The scientific support for these guidelines is drafted by the Dietary Guidelines Advisory Committee. I served as a member of the 2010 Dietary Guidelines Advisory Committee and describe the challenges of translating evidence-based nutrition science into dietary practice.