It may be difficult to answer your question based on little information. Since the scope of practice and liability becomes important here with regard to how much nutrition information a trainer can give. Specifically what do you plan on offering your clients in the way of nutrition? If you are opening a personal training facility, will you offer basic coaching or general nutrition guidelines? You may be able to do some basic nutrition guidelines with a nutrition or health coaching certification (for example, ACE has a Health Coaching Certification for adults that is very good). Or, more specific meal planning? That should require a Registerd Dietician.
They are very different avenues and require different levles of education, so it may help to elaborate on what services you plan to offer.