Hello. I am 3 yrs out (this month) from my laparoscopic robotic-assisted Total Colectomy with Ileo-rectal anastomosis. (TC-IRA). Your question is VERY important. My surgeon told me similarly; eat 35 grams of fiber per day, soluble or insoluble. I began adding fiber gradually, tried various types of fiber supplementation and foods. It didn't work out too well for me and I believe that this advice is thrown out in a cavalier manner. My experience may be different from others as I also do not have a gallbladder so this affects my digestion (bile dumping and the irritation that this causes upon exit). So, I was very keen on "figuring" out my diet. I'm still working on best practices.
The small intestine is now doing the work of the large intestine. This will take time to acclimate to its new job. I tried adding psyllium husks and it slowed things down, but it's very harsh on the small intestine. It turns into a gel and caused me a lot of pain and pressure. Think a scraper rather than a smooth movement. It also binds with medications and supplements and can make them less effective. So, timing and dosage is important. After a while, I stopped the psyllium because I didn't feel well. I have to be monitored due to genetic polyposis issue, and a CT revealed that I had a "blind loop" at the anastomosis. It was confirmed at my annual sigmoidoscopy (even tho I don't have a sigmoid portion, I have annual scopes to check out anastomosis and rectum for polyps). I'm not sure what caused the loop. I read that some TC patients can develop this loop after many years, but mine showed up in year 2. But I suspect it was too much harsh fiber. The blind loop can pool waste at the site and become stagnant stool creating issues like SIBO. I tested negative for SIBO for two years, so I'm happy about that. I also have significant upper digestive issues so have controlled acid reflux and have an annual scope there due to polyp burden. Yeah, I'm a walking polyp farm. (or was until I had my colon removed).
I can't eat skins of fruits or veges, seeds, gassy veges, lettuce or cabbage, heavily seasoned foods with garlic and onion. I peel everything. No more salads. I do gentle fiber such as instant oatmeal, canned fruits, eat meats and poultry, sourdough or white bread, Natures path fig bars, potatoes, sweet potatoes, green beans (canned), pasta and sauce (I cut the acidity a little with cream), peanut butter, eggs. I indulge on potato chips and chocolate. I recently added 1/4 tsp of cholestyramine (a cholesterol medicine powder that causes constipation and is frequently prescribed for slowing things down), but easing into it to avoid a small intestine blockage and timing around medicine intake due to it's sequestering properties. It has changed things a little, but will creep up on the dose. My main concern is the irritation caused by the bile acid malabsorption (BAM) more related to no gallbladder than no colon.
Overall, I'm very happy with the surgery and I do have great control with my movements which allows me to travel, exercise, etc. Basically, I live a normal life. But, I do believe that going very gentle with this process is essential. Try a food, keep a log, be prepared to pivot if it causes issues. It's not just a "eat a bunch of fiber" solution as we've both been told.
I hope this helps. You're welcome to message me with questions.