Since 2005, the Federal Dietary Guidelines for Americans (DGA) have recommended that people eat at least half of their grain intake in the form of whole grains. Whole grains contain all parts of the grain kernel; the process of refining grains removes some portions that contain vitamins, minerals, and dietary fiber. In the United States, most refined grains are enriched with some vitamins (thiamin, riboflavin, niacin, and folic acid) and iron that are added at federally specified levels. Nevertheless, the DGA recommend whole grains as important sources of under-consumed nutrients such as zinc, magnesium, and dietary fiber. They also cite evidence of a relationship between whole-grain consumption among adults and reduced risk of some chronic health problems. Among children and adolescents, there is evidence of a reduced risk of obesity in adolescence and of cardiovascular disease in adulthood, although the expert committee that advised the Federal Government on the DGA judged that evidence to be limited.