I had a total colectomy (but my rectum was left) and am getting an ileostomy in eight days (getting so nervous about going into hospital now!).
You will be more prone to diarrhoea without a colon, as the colon absorbs water from stool. So when it's gone, more water remains in the stool. So you need to drink a bit more to ensure you replace the extra water that's being lost. I was told you need to eat more salt when you've no colon also, because the colon would absorb salt back into your body.
But diarrhoea can also be caused by problems further up your digestive tract. E.g. if you have Crohn's in your small intestine this could be causing (or contributing to) the diarrhoea.
As for diet; I've been reading up on the best kinds of things to eat with an ileostomy. It actually doesn't seem much different from how you'd be advised to eat if you were prone to diarrhoea even if you have a colon: low fibre, low residue. And there are some foods that can help slow things down a bit: eggs, smooth peanut butter, white rice, applesauce, white bread, bananas and cheese. There were probably some other foods too that I've forgotten.
