Experimentation seems to be the best way forward after a colon operation. I'm 77 and had a colorectal resection a month ago to remove a tumour along with 10" of colon and was a bit nervous at first about what to eat, not wishing to stretch the new joints in the pipeline. But on the whole I've been pleasantly surprised at how easy it has been - some initial diarrhoea / constipation but a mild laxative cured the latter and now I'm eating like a horse again with lots of boiled / mashed potatoes, pasta, noodles, green leafy vegetables, carrots, fish, chicken, tomato juice, muesli and bio yoghurt. I've cut back on red meat and alcohol. So plain food on the whole although I did have a South Indian curry and a beer a couple of days ago, with no after effects! This diet seems to work quite well for me and I hope for others too.
I think plenty of exercise helps - my target is 5,000 steps per day but I only achieved that 3 times over the past week.