A nutritionist is someone who believes that the nutrients and toxins you consume affect your health deeply. They believe food is medicine. Consequently they teach people which foods are healthiest, how to find them, how to avoid lesser ingredients, and how to prepare the foods to be delicious and enjoyable.
You want a nutritionist who knows how to determine your metabolic type, assist with testing for food intolerances, increase your tolerance to said foods, test for hormonal, nutrient, and intestinal imbalances, and create a dietary plan that is customized to your needs based on these and other factors. A nutritionist should never diagnose illness (candida, leaky gut, adrenal fatigue, hypoglycemia, etc.), recommend a one-size-fits-all approach to food, recommend severe detoxification or fasting programs, or advise regarding pharmaceutical medications or treatments. These are over simplistic or beyond the scope of our training and ultimately indicate a poor understanding of nutrition and how to re-establish and maintain health.
In short, you want a nutritionist who will work with your preferences and lifestyle, with your chosen therapies and physicians, and with your goals and body type. You should see noticeable improvements in your health within 3 months. I have never had a client whose health is not greatly improved, if not completely turned around, within 6 months.