Judging from the skeletons they left, our hunter-gatherer ancestors were healthy without need to pay much attention to diet beyond doing their best to get enough.
In particular, they had no difficulty getting enough fiber: there was plenty in everything. Our problem is that our whole food-industrial complex is devoted to stripping out and discarding the fiber we need.
If 40% of Americans didn't brush their teeth or bathe, we would have a hygiene problem of a magnitude commensurate with our health problem.
Roughly that percentage of people don't take sufficiently-good care of their teeth, yes. But brushing one's teeth (and bathing) is easier than resisting food cravings.
The value of fiber (apart from keeping some nutrients indigistible and hence less calories for obese people who need to eat less) is still a matter of debate.
In particular, they had no difficulty getting enough fiber: there was plenty in everything. Our problem is that our whole food-industrial complex is devoted to stripping out and discarding the fiber we need.
If 40% of Americans didn't brush their teeth or bathe, we would have a hygiene problem of a magnitude commensurate with our health problem.