Nutrition is a very “iffy” area for fitness instructors. The ACSM provides the limit on what we are techniquely able to discuss with clients. A lot of fitness instructors sell supplements and even provide menus/food suggestions that actually are outside of our scope of practice. You may feel that you have the knowledge to do this, but I doubt it. As one in every 100 people taking heart and blood pressure medication are potentially at risk of serious complications from eating something that interacts with their meds. Grapefruit alone has serious known interactions and effects with over 100 popular prescription medications. I guide clients with the information that I am permitted in my scope of practice.
If I feel a client needs more assistance, they go to a Registered Dietician. You may be fine with exceeding your scope, but I find the possibility that something you suggest to a client could be harmful to be an unacceptable risk. If you feel that diet is a part of health you would like to persue, by all means go to college and become a Registered Dietician. You can kid yourself that diet and health safety aren’t that serious, but I certainly would not one of my family members taking advice from a person who read a book or took one CEC course on nutrition. I have taken over a dozen nutrition CEC courses, but only advise as is in keeping with my scope of practice. The courses were for knowledge and personal use. And to help me understand my scope better.
A number of people in here will feel that I am wrong. I only hope that they never suggest a food to a client that seriously harms the client. Even one out of one million is too great a risk for me to take.