it is a fuzzy situation. You can make generic recommendations such as ‘research suggests to have x grams of protein per day in your diet’ rather than ‘YOU need to eat 100 grams of protein per day, and here is what I want you to eat’.
There is a lot of room for imparting information, though, without overstepping boundaries.
you even have to obtain a licence when you are a registered dietitian. Here is a sample from the website of the State of Georgia.
“I am a registered dietitian. Do I need a license to practice in Georgia?
Yes. You cannot use your registration to practice in Georgia. You must hold a valid license issued by the Georgia Board of Examiners of Licensed Dietitians in order to practice dietetics in Georgia.”
There are many resources to answer your question. Here is one link http://www.nutritioned.org/registered-dietitian-georgia.html.
Having a certification in fitness nutrition, no matter from which organization, probably does not suffice for the requirements for most states to obtain such a licence.
You should check first with your insurance company. If you are offering a new category of services you want to make sure you are covered. You can also ask them the question about legal scope of practice in your state. Depending on that answer it would behove you to get legal advice. You might check to see what low cost legal services are available in your area, if you do not have a lawyer you use for other things.
It is also important to think not just about what the law and your insurance allows, but what you feel ready to do. Simple answers about the value of healthy eating are one thing. Dietary plans can lead into possible problems…. underlying allergies, health issues, interactions with medication, the fact that supplements are unregulated,…. Have a good plan before you go forward, and try to keep to that. I teach mindfulness in relationship to food, in the contest of my beginner mindfulness class. I also occasionally talk in broad terms to my students about metabolism, current research, ethical eating issues as they relate to yoga, and so on. I could see doing a workshop on the relationship of food, exercise, and mindfulness training. But I think it is important for us as professionals to go a step beyond simply painting within the exact lines the law allows.