The dietary principles that must followed in order to maintain a sufficient intake of essential nutrients. These principles include variety, balance, and moderation. The earliest nutrition recommendations can be traced back to the late eighteenth century when the Industrial Revolution in England caused a rise in urban populations with large numbers of homeless people. The United Kingdom published its first set of dietary guidelines in 1994, and they have been regularly updated. The version of Eating Well with Canada's Food Guide was published in 2007. The National Health and Medical Research Council released the new Australian dietary guidelines in February 2013. The United States published the eighth edition of its Dietary Guidelines for Americans in January 2016. The Dietary Reference Intakes (DRIs) represent a set of four types of nutrient intake reference standards used to assess and plan dietary intake. These are Estimated Average Requirements (EARs), Recommended Dietary Allowances (RDAs), Adequate Intake Levels (AIs) and Tolerable Upper Intake Levels (ULs).