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.