This law provides for the licensure of dietitians, and only those with a license may provide nutrition care. Under this law you cannot advertise or be perceived as “assessing nutritional needs of individuals and groups” etc. You also cannot do or say anything that would give the impression that you are licensed, registered, or call yourself a nutritionist or dietitian.
You can provide general nutrition information as to the use of food, food materials, or dietary supplements, as well as distribute nutrition literature, so long as you do not call yourself a dietitian or nutritionist.
You can also practice nutrition with the supervision of a licensed dietitian or licensed nutrition. This includes:
If you are licensed in a separate medical profession, you can engage in the practice of dietetics if you do not call yourself a “dietitian.” This includes dentistry, medicine, osteopathy, chiropractic, nursing, or pharmacy.
You can market or distribute food, food materials, or dietary supplements and further explain how to use or to prepare those products.
Source: Title 15, Part 19, Subpart 60, CHAPTER 3
Regulations can be found here