It was because of you and this thread that I decided to post the following:FREE: Digestion SOS Docusummit (June 21-29, 2021)https://www.healingwell.com/community/default.aspx?f=30&m=4252515
Though I'm skeptical of many of the advertised "experts," I'm also aware of the remote possibility that you might find something helpful, regarding the initial questions and symptoms you posed.
My non-expert opinion is your gut health seems enviously healthy! Personally, I wouldn't worry too much about
the occasional bits of undigested food, unless you're showing any overt signs of nutrient deficiencies
Otherwise, my understanding is that nutrient absorption fluctuates, depending on what the body needs at any given time. (The gut becomes more or less permeable, as one example, to uptake more of less of various nutrients.) There's also factors like the composition of meals -- such as ingesting some fat with foods containing the fat-soluble vitamins, pairing Vitamin C-rich foods with iron, and other things you already know.
Following is an article that may be worth considering. It's written by a board-certified, licensed nutritionist that I find to be level-headed:How Much Nutrition Do You Absorb from Food?https://www.quickanddirtytips.com/health-fitness/healthy-eating/know-your-nutrients/how-much-nutrition-do-you-absorb-from-food
There are also varying opinions about
the nutrient composition of soil, the healthfulness of organic vs. non-organic foods, the debate whether modern foods are less nutrient dense than 50-100 years ago, etc. As with most topics, there are endless wormholes down which one can travel -- which I do not recommend.
In the end, even if the soil is less healthy and foods are less nutrient dense, the best solution is simply to push a higher volume of food through the body...while also remembering that the body controls absorption. Fortunately, it seems that the foods richest in beneficial compounds are also those lowest in calories.
If only ice cream were a vegetable...