I agree and found the same as you. In 2014 iv decided to go on a "vegan" diet, mainly consisting of fruit smoothies with oatmeal, whole grain breads, pasta, vegetables etc.. "healthy", sometimes eating up to 50-100 grams of fiber a day not even a year later I get diagnosed with crohns disease, a perianal fistula and intense pain and cramping especially while having a bowel movement. I was in denial it was the diet because everything I read was to eat more fiber, fiber for gut health. My symptoms only got worse developped a bladder fistula, refused medication and surgery although I did take antibiotics which helped.
After years of research iv came to the conclusion that fiber is not so good afterall. I followed a carnivore diet symptoms improved after just a few days. It was amazing for my gut but I had no energy and became depressed. Thankfully I found ray peats work, and stan efferdings vertical diet. This has changed my life. I have found that I cannot tolerate fructose, dairy, gluten and I avoid fiber at all costs. I eat beef, eggs, white rice, salt, liver once a week and fish once a week (low pufa). That is all and I feel amazing, my fistulas are healing, my energy through the roof iv never felt better in all my life. Eventually im gonna introduce some fruit and later hopefully I can tolerate dairy.
I supplement vitamin d3, magnesium, k2 once a week.
Had somewhat of a similar experience. Prior to my experimentations with Keto, IF, Paleo, Peat, and now some principles from all the above, I tried a so called "healthy diet" while I was in highschool. It included white meat only, oats, lentils, lots of greens, vegetables juice, olive oil and whole wheat bread. Wound up having severe digestive issues, dropped down to 145lbs at 6'2 from 185lbs and had my gallbladder taken out at 18. Digestion hasn't been the same since (easily irritated by certain foods) but I've gotten significantly better and solved many issues on a diet of meat, seafood, eggs, saturated/ monounsaturated fat sources, fruit, fruit juice, and certain tolerable veggies. I currently dont eat much starch, but when I did the only starch I tolerate well was white rice and white rice products.