Six states and the District of Columbia sued the Department of Agriculture on Wednesday, saying it weakened nutritional standards in school breakfasts and lunches when it relaxed the requirements affecting salt and refined grains last year. The lawsuit in Manhattan federal court asked a judge to overturn the changes, saying they were carried out in an arbitrary and capricious manner.The government “significantly weakened” nutritional standards for sodium and whole grains, according to the lawsuit, without giving the public a chance to comment on them and in opposition to nutritional requirements for school meals set by Congress.The states and D.C. said the standards should be based on recommendations of the U.S. government’s “Dietary Guidelines for Americans,” the National Academy of Sciences and scientific research regarding children’s nutrition.