Final answer:
Federal regulations to implement a law affecting dietetics practice post-Congress approval are prepared by the Department of Health and Human Services, typically through the Food and Drug Administration.
Step-by-step explanation:
After Congress passes a law affecting dietetics practice, federal regulations to implement the law are prepared by the Department of Health and Human Services (HHS). The HHS is a federal executive department responsible for health and welfare, which often acts through its agency, the Food and Drug Administration (FDA). The FDA has the authority to oversee the quality of substances sold as food in the United States and to monitor labeling claims about the composition and health benefits of foods, as mandated by statutes such as the Federal Food, Drug, and Cosmetic Act. This act and others like the Public Health Service Act, are enforced by the FDA which is led by the Commissioner of Food and Drugs. This commissioner is appointed by the President with the advice and consent of the Senate.