No. ANYONE can call themselves a nutritionist in most states. It takes no formal education or certification. All you have to know is how to design diets and get results. And most guy with nutrition certifications were already writing diets before they got them.
I am a registered dietitian with degrees in nutrition, which is a different story. So long as you do not intend to or pretend to reat any medical conditions (eg, morbid obesity, diabetes, renal disease, post-bariatric surgery, pregnancy, anorexia and bulimia, or anything that has to do with nutrient-medication interactions), you can pull it off.
If you are gonna go for a cert. I recommend John Berardi's Precision Nutrition or the ISSN's sports nutr. certification (this one requires a science or life sciences degree). Both companies have solid staff (Registered dietitians included) that designed the material. One of the co-founders of ISSN was one of my professors, and he was awesome.