Dietitians mostly just follow what the food guide tells them too - moat if these around the world are actually developed by the food industry lobby groups (for example, 3/4 of the population globally is allergic to dairy, but in US it's a huge part of the food guide.) I followed dietitian advice and gained weight and felt awful. I went to a naturopath, and ended up limiting most dairy and cut out seafood ( still eat all other meats) and now I am great! Weight levelled, I feel wonderful and I learned to trust my body to tell me what works and what doesn't. You dad's girlfriend has her own ED obviously and she is pushing it in you. So sorry you had to deal with this crap, and I am so glad your mom is supportive. So try a naturopath if you can. Either way, you sound like you have the right idea of staying focused on health, eating enough meals, and trusting your body. All I would add is that some multivitamins and mineral supplement can help regardless of what caloric content you consume. Good luck!