I don't obsess so much about food now a days because apparently that's also a slippery slope that can develop to an eating disorder ( orthorexia - see https://www.bu.edu/articles/2013/when-healthy-eating-becomes... ). I however do understand your concern and I think one of the reason why we may be having a difference of opinion on this is because of culture - as an indian, my diet is quite different from a western one, and some of you may indeed require to change your diet to incorporate more fibre rich food or even supplements. My mode of monitoring my fibre intake is to just observe my poop - if it's too hard, there's too much fibre in the diet, and if it's too soft, there's less fibre. Eating a balanced diet, maintaining my weight, exercising, and adjusting my diet as per my annual health check-up is the routine I've adopted now (e.g., I've added chicken liver to my diet this year on the advise of my doctor because some vitamin level was borderline).
I think you're right about diet. When I asked my first doctor about diet - what should I eat and not eat, he told me something counter-intuitive. He said "it changes back and forth every year, but one thing is agreed upon - eat a variety of foods".
A lot of my indian colleagues behave quite differently from the general population. They frequently cook at home and/or for themselves and bring the food in, and they generally use whole/individual ingredients. I've also heard that indians don't get alzheimers because of turmeric.
That said, as people age or become more sedentary I think proper fiber becomes very important.
I've tried it and it is hard.
Let's say you need 38g of fiber per day and you need to make up half of it.
You could eat 6 cups of brussel sprouts, or sprinkle 6 packets of benefiber on your food as you eat throughout the day.
Also, a lot of natural fiber in quantity has some unpleasant gastrointestinal side effects.
I'm not saying it is impossible, but it can be quite challenging to get all your fiber from natural sources in our society.