Hi Andrew. :welcome:
I also have had a proctocolectomy and about one third of my small bowel removed as well.
How are you recovering from the surgery? It took me a long time to recover because I had left it so long that the area around the rectum and anus was very badly damaged.
I gained weight once things had settled down and I had worked out what things I could safely eat (I had lost a large amount of weight before the op.). Some people find that they can eat almost anything but I still have to be a bit careful.
I am fortunate that I get enough iron and B12 from what I eat, but you will neeed to have these and Vit D checked. In fact I have thorough blood tests every 12 months to keep a check all of this stuff.
You will also need to keep a careful watch on your hydration as our bodies rehydrate from the large intestine and yours will no longer be able to do this. My belief, from personal experience, is that other parts of the digestive system learn to perform some of this function, but certainly not all. My big problems, in this regard, come if I am vomitting and also have diarrhoea. Then I have to be very careful to make the decision to go to ER before my brain stops making rational decisions.
Please ask any questions that you want - someone will usually be able to answer them or, at least, give you some some ideas. :hug: