My father was a large animal veterinarian from the 50s to the 70s. Around 1960, he noted that post-war genetics and feeds (then protein heavy), had created a kind of Franken-cow, one that produced 2-3 times as much milk, but were sometimes dying of ketosis (which my father's Cornell prof said was a "fancy word for starving to death"). My father would give these cows a bottle of dextrose, the cow would "get well" and he'd get paid, but he felt guilty. He then consulted others, and set about making feed rations with more fiber, trace minerals, and of course more carbs. People had a hard time believing that things like almond hulls were as good for cattle as alfalfa. When I ate cereal as a kid, my father would joke that I'd be better off eating the box it came in. He got opposition, but was ahead of his time (almost as much production, fewer vet bills, less cattle death). the industry eventually came around.

I believe every question about diet needs to be prefaced with one's activity level (and age). Of course heavily milked cows would be like triathletes. When life slows down for us, maybe less carbs and more fiber. Your gut basically tells you whether you're getting enough fiber (it seems to be the engine's lubricant).

If you've ever been as old as me (68), trying to get your 35 gm of fiber/75 gm of protein daily, you start realizing that those two come in mutually exclusive packages (fruits/veggies for fiber, eggs/dairy/meat for protein). The carbs/fats seem to take care of themselves, although I try to lay off the "cheap carbs" (pasta, mashed potatoes, bread). Nuts/legumes are among the few things that contain both substantial protein/fiber.

I suspect at my age, the margins of error are less, and regular exercise and portion control may be as important as what we eat.