For me, I lost 50 lbs not exercising and not actively managing my diet. I felt better and all my biomarkers got better (blood pressure, cholesterol, etc.). Later, I started to exercise and cleaned up my diet because I wanted to. Healthy food just tastes better now, and moving my body is satisfying rather than tiring. They are the closest thing to magic I’ve ever experienced.
Also, constipation and muscle loss are real issues. Protein and exercise will help with muscle loss (well, I haven't really started weight training yet, just aerobic), but you need to up your water and fiber intake or you could be in for a very hard time. I'm glad that this didn't happen to you, and that you didn't have to take an emergency trip to the drug store to figure out what an enema was (and how to use it, ouch).
The only time you need a dietician is if you want a high enough dose you barely want to eat at all.