I eat lots of raw fruit and veggies so I get lots of fiber.
I did this for a while thinking that fiber was important to proper elimination. After converting to a diet of only meat and fat, I've now come to believe that fiber is really bad for our intestines and that we were never designed to eat much of it. There have been studies showing that the conventional wisdom that fiber "sweeps like a broom" and helps prevent colon cancer is total nonsense. There is actually a slightly higher rate of colon cancer on a high fiber vs low fiber diet. The rates of Crohn's Disease, IBD, and Ulcerative Colitis, on the other hand, have reached epidemic proportions on a high fiber diet but very rare on low fiber diets. Fiber is more like sandpaper and irritates the bowels making things worse not better.
I think lots of fibrous foods is very Paleo.
My research and experience have brought me to the opposite conclusion. I've attempted to live off the land eating carbs and found it next to impossible. Wild fruits and veggies are nothing like what you find in your local market. Wild fruits are small, mostly seed, and usually very tart and often down right sour. Wild vegetables are tough, stringy, very bitter and pretty much indigestible. Even the acorns that the local Natives used as a survival food when game was scarce is so bitter from tanic acid that they must be ground and then the "flour" soaked in hot water to make them edible. Even the birds won't eat them. The woodpeckers get the acorns that have insect larvae in them, store them in cracks and then come back when the larvae have matured, crack the acorn and eat the larvae. The Journals of the Lewis and Clark expedition don't support your conclusion as related to Native North American Indians as they much preferred meat to any other food source. Carbs were a survival option only. The lastest anthropological studies of protein tracers in the bones of pre-neolithic man show that they ate a diet composed in excess of 95% red meat from terrestrial animals - almost zero carbs - thus zero "fiber".
This doctor on the Oprah show talked for a half hour about poop. If the crap stagnates in your gut it can cause medical problems.
I used to believe this myth also, however when eating very low carb diet this does not seem to be the case and actually the opposite is true. Remember that our doctors and clinics are dealing with people who have been eating a carb based diet and have zero experience with people eating a meat and fat based diet. Meat and fat are both fully digested with very little waste and almost no nutrients in the waste to support large colonies of bacteria in the gut. Carbs, and especially fiber, are indigestable and leave a large nutrient load in the gut providing firtile ground for bacteria and fungus to grow.
I once read (though can't remember where as it was many years ago) that bacteria and fungus make up almost 80% of the bulk in the bowel movement of a person eating a high carb diet rich in fiber. On a meat diet our bodies efficiently extract all the nutrients from the food leaving little for bacteria and other critters to survive on. This substantially lowers the bulk of the stools of a meat eater compaired to someone eating significant carbs.
The High Fiber theory just doesn't hold water when you leave the supermarket and try to exist on truly wild foods, especially when you consider that there were no pots and pans in paleo times so boiling water to soften otherwise inedible food was not possible. Go out into the woods sometime with a sharp stick and some rocks. Go ahead and take matches for fire but no shovels, pots, pans, dishes, or cutlery-including knives. This is what paleo man was faced with. See what plant based food you can find. I think you'll discover that taking down large animals is the only practical solution.
The idea that carbs were a significant part of our human diet throughout history comes from researchers and professors, sitting in their climate controlled offices munching "healthy" sugar soaked "whole grain" granola bars loaded with "candied" bits of fruit.
My 2 cents,